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Bryan teaches the Kalos technicians about electric heat, often used as supplementary heat in heat pumps and furnaces. He also shares some stories from the field and teaches the techs a bit of math.
Heat strips are one form of electric heat. It would stand to reason that taking a bit of heat strip off wouldn't hurt anything, but the electric heat would be less effective. However, when you factor Ohm's law into the equation, you'd be taking off part of the heat strip and reducing the resistance, meaning that the amps will increase. Heat strips also burn out when they touch another piece of metal, like the casing around it, because the amp draw becomes much higher.
Electric heat has some benefits, including its consistent BTU output (3.41 BTUs per watt); regardless of the outdoor temperature, you can expect the same BTU output all the time. It is also reliable and usually easy to work on. However, it is inefficient. Electric heat is the baseline of COP (coefficient of performance), and a pool heat pump that has a COP of 3 is three times more efficient than just the electric heat.
Electric heat has other issues, including odors or smoke when it first starts after a long time of inactivity. (It's easy to burn off the heat strips on a PM, especially if you jumper W to R or use the thermostat to burn off the heat strips.) Electric heat also causes high bills when it runs too much and causes stress on the electrical service. Electric heat elements also draw very high current, so you have to manage your wire sizing and electrical connections. You can also encounter mistakes with blower interlock; you don't want to run the heat strips without the blower running.
In a 4.6-kilowatt (5kW) heater, you would divide 4,600 by the unit's rated voltage to get the amps of electric heat. The wattage decreases when the voltage decreases because of Watt's law. When you put more voltage (electrical pressure) on the circuit, you get more current. So, the total watts would decrease if volts or amps were to decrease. If you divide the watts by voltage, you can find out your amps. To find the BTU output, take the watts (volts x amps) and multiply them by 3.41. You can also use Ohm's law to find the resistance. Take the voltage and divide it by the amps to get the resistance (ohms). The voltage is a moving target, but resistance stays constant for the most part.
The data tag should tell you the proper wire size to feed the air handler; look for the MCA (minimum circuit ampacity) to help you make your decision. Keep in mind that 5-kW heaters are not necessarily 5 kilowatts.
When it comes to terminals, you have W, W1, W2, W3, and E. W is just heat; it is usually just for a single stage of heat. W1 means first-stage heat; it indicates the compressor with the reversing valve de-energized. W2 means second-stage heat and can refer to electric heat. W3 is the next stage of heat, and E is just for emergency heat. We used to have to jumper Y1 and W1 and a few other terminals together on older thermostats; they perform similar functions, but the reversing valve would distinguish heating from cooling.
When testing heat strips, you can usually (but not always) expect 5kW heaters to draw 20 amps and 10kW to draw 40 amps but still 20 amps per strip. However, the way you read the amps can change based on the voltage (230v vs. 208v). Commercial buildings often have 208 volts supplied to them because they are hooked up to two of three power legs.
Heat strips also have thermal limits; therm-o-discs can be found on the high and low sides for extra protection. These discs also have temperature ratings on them. You can tell if the thermal limits are open by ohming them. If they are open, you'll measure OL or infinite ohms. If they are closed, the ohms will be low.
To control the electric heat, a unit will have either a contactor or a sequencing relay. Sequencers have contacts that close at different times. You don't want to use a 90-340 relay, but we sometimes use those for a fan interlock.
When using a 90-340 for the fan interlock, you must set it up correctly as not to melt the relay; the current from the heat strips should not go through the relay at all. To avoid confusion as much as possible, follow the wiring diagram and think of the relay as upside down.
We can also stage heat strips if we have more than one. Staging makes the unit draw lower inrush current and use less electric heat (the less you use, the better).
When testing heat strips, you can use three methods: measure the heat strip amps, test on and test off, and force the system into defrost to test the heat strip amps.
Heat pumps with supplementary heat may have special code considerations when wiring to the outdoor thermostat, which you must keep in mind.
Read all the tech tips, take the quizzes, and find our handy calculators at
Learn more about the 2022 HVACR Training Symposium at

All right so we're going to talk about electric heat. Electric heat is electric woogie, woogie woogie, to quote the electric slide. This is turning bad, really bad um. We already talked a little bit about electric heat when we did the heat pump, heating, diagnostic and troubleshooting and servicing section, but we're just going to kind of keep rotating rotating through as we go.

So one thing you are going to need is you're going to either need the calculator on your phone or a scratch pad with paper. I think we'll do the calculator on your phone uh for most of you here, because we're going to do just a little bit of math. Just a tiny, tiny bit bert attempted to do some of this in his class, and i think it's helpful when you're going to give a class for something that you actually know what you're talking about before you give the class. That's usually something that i advocate for not that i'm picking on bert we're going to do just a little bit of math we're not going to focus on math, because math is not the main thing.

With this we're mostly going to focus on just the relationships. What happens when different things change with electric heat? So the first thing is, i always start with a story. I've told the story like a thousand times so if you've heard it before, you know what story i'm gon na tell sam, which one which one is gon na, be because there's two okay, the bank yeah. Okay, do you want it? You want to tell that one better.

Okay, it's better! For me, okay! Well, i wasn't gon na tell the bank one, but we will tell both i'll tell both stories. Actually, let's just start with both stories, you know start with the you know don't bury the lead. Is what they always say? So the bank story is, i was probably i was sorry 19.. I was doing maintenances for a bunch of suntrust banks.

They used to be called sunbank back in the day and i was actually doing the maintenance on the one in claremont and they have a big rooftop unit that does most of the bank and a couple splits. But i was going through and i was testing the heat strips because i was told that that's what you're supposed to do so i was running them in heat and i was doing it just by jumping out to white, so jumping red to a red to w And heat trips would come on and i would check the amperage and whatever well. I was doing that and um as i was doing it because i had to set an extension ladder up against the parapet wall on this bank uh, the manager, the bank manager came up poked his head up and said what the heck are you doing. There's smoke blowing everywhere the bank's on fire, and so the so i'm like okay shoot and i come down and sure enough.

There's just i mean they've already got the doors open, there's smoke billowing and the fire department's already uh already pulling up. Well, as it so happens, my parents back there, and so my dad shows up while this is all going on hey what's going on, you know: let's talk about it for half an hour and uh, so i, finally, you know we got it all cleared out. Of course, i wasn't very popular in the bank and then got done with all my maintenances left and then i was, i think i was either on call attack or the on-call tech called me, and i was like what did you do? The bank is like 95 degrees, something like that um, maybe it wasn't even on call. It was just later in the afternoon because banks aren't open that way, so this story isn't really working too well but anyway, so it's really hot in the bank, and so i show up and yeah it's like super super hot.

I go up and the this package unit was a heat pump and it was running in heat mode so like what gives, as it turns out uh when they had originally wired up the smoke alarms. The smoke alarms were supposed to break red in order to shut the unit off and the smoke alarms went off well, they didn't they broke orange, and so, when you break orange, you have no 24 volt call on your reversing valve and it just locked the thing In heat mode, and so i didn't test out the way i was supposed to so a couple mistakes there, one is: whenever you're going to check electric heat, especially if you don't know when the last time it's been tested, you need to talk to the occupants. If you think it's been a really long time like in a commercial application where maybe the heat strips have never run, it's a good idea to just pull them out, and you know clean them with some compressed air, nitrogen or something like that, rather than burning them Off so that's the lesson there. That was a great story.

Wasn't it i feel, like i really told it dynamically there. You didn't know about the about the no. That was that was true. It's true, i didn't make it up.

I just haven't told that part before, so that's just a lesson in being thorough um i was, i was thorough, but i wasn't communicative about my thoroughness and then i wasn't throwing the end and testing out the other story is about. I forgot what the other story is hold on hold on hold on what was the other story that i always tell about electric heat? Oh, there is actually another story that i'll tell a little bit later about wire sizing. That's another! That's another key one that we'll get to um. Oh, that was the other story i want to tell was.

I was working on a package unit uh in leesburg, actually very close to where you live nowadays. Sam. I know that adds to the story just having that personal connection to the story: yeah, okay, so we're on a package unit and back in that at that time the company i was working for they would give us heat restring kits, so they had a failed heat Strip, it was shorted out or open or whatever was actually burned, and they gave us this kit, a five kilowatt heat restring kit, so it had the entire thing. It was in a little plastic bag and you were supposed to take it and restring.

This whole thing and put it back on the insulators and all that that's what we had on our trucks first time, i'd ever done it so, as you can imagine, i kind of bungled it as i was making the terminations or whatever it kind of kinked and, Like broke and it was in bad shape, so i thought well, this customer, you know it's just heat strips, so if i take a little bit of heat strip off, you know just a little bit the part. That's broken, that's not going to hurt anything. It just won't heat quite as well right is that standard reason stands the reason that if you take a little bit of heat strip off it just won't heat quite as well. Everybody agree with that.

There's still heat it just won't eat quite as well. Just took a little strip off right, okay, here's the problem with that. I i knew ohm's law and watts law, but i didn't pay very close attention to it and i don't care that you know how to do the math or don't know how to do the math, but ohm's law is e, equals i times r okay. So that means that voltage equals amps times resistance.

Well, in this case, the voltage is fairly fixed going into a unit right. So that part is the part of the equation: that's fairly fixed, so we'll say that our voltage is 240 volts, so 240 volts equals amps times ohms all right. So if 240 is fixed - and i change ohms - which is what i'm doing when i cut a piece off of that heat strip - and i change them down - does my amps go down or up if i decrease my resistance, the amps go up. This is a very simple concept, so you don't need to know the math.

You decrease resistance. Do you get more flow or less flow? You get more flow right. You decrease resistance in a pipe. Do you get more or less water flow? You get more flow.

You decrease the resistance, you increase the resistance, you get less flow easy, and so what did i do? When i cut a piece of heat trip off? Did i decrease the resistance, or did i increase the resistance? I decreased the resistance. I took some of the coil off. If you take some of the coil off, there's less resistance to electricity. Do i get more current or less current? I get more current.

So what happened was i took a piece off and when i lit it up, when i fired it up, it was drawn high amps and the thing was glowing red and didn't work right. So and i don't know maybe it wasn't. Maybe it was glowing red because i was testing it without proper airflow over it. Who knows at that time i was a dummy and didn't know anything.

So it's hard to know what exactly i was doing. But the point is that with heat strips, if you reduce the resistance you're going to get more current, and so that's what happens sometimes, when heat strips touch something touch a piece of metal, you create a short circuit path and they will burn out because they're drawing Too much current makes sense. So it's important when you install heat strips one of the most important things is that you don't short them out. You don't shirt them out to the casing around it.

You don't short them out to each other, pretty obvious. So you, you will run into cases where things will lay across here just in the installation process. Sometimes they're. You know something like a piece of duct board or a piece of cardboard or something which will catch.

You know the cardboard will catch on fire. The duck board won't do much other than block airflow, but sometimes it could be metallic and that can lead to heat strip. Failure make sense so make sure. That's that you don't do that benefits of electric heat.

That's what we've got up on the on the screen here. One nice thing about electric heat is the math is really easy. With electric heat, one watt equals 3.41 btus all the time. So here's a question this heat strip here.

Is it more or less efficient than an electric space heater? So if i took this to heat, the house, or i heat a house with a bunch of electric space heaters which is more efficient, this right agree. You agree, this is more efficient. Well, no there! It doesn't matter in terms of now you could, if you want to add in the little motors for everyone, maybe it's a little more efficient, but in terms of the heating function, with electric heat strips no matter, if it's a little tiny heat strip on a space Heater, no matter if it's an oven, coil, no matter if it's the the element on your oven or on your stove they're, all going to equal 1 watt in equals 3.41 btus out just that simple, and so when we, if you've ever heard of cop coefficient of Performance cop is a measurement where you compare the efficiency of a refrigeration device or some other device that moves heat around to electric heat and it's always more efficient. So a typical cop for a pool heater, for example, would be like a cop of three something like that, which means that it's three times more efficient under normal operating conditions than if you were just running electric heat to heat.

The pool makes sense because, in the case of electric heat, we're taking electrical energy and we're converting it directly to heat energy electrical energy directly to heat energy in the case of the refrigeration circuit. What are we doing? How? What are we doing with heat ronnie refrigeration circuit? What are we doing with heat, getting rid of it? We're getting rid of it but we're moving it from one place to another place, so we're not taking one form of energy and converting it directly to another form of energy, we're taking energy from one place and moving it to another place. That's the definition of refrigeration is to move heat from a place that it is unwanted to a location to where it is unobjectionable. You remember that one unobjectionable, that's what it is, we're taking heat and moving it from a place that we don't want it to a place.

We don't care basically right, but in electric heat, we're taking electricity, turning it straight to heat, so it's not efficient, but one nice thing about it is we can count on it. We know. What's going to be produced, it doesn't matter it doesn't matter if it's 0 degrees outside doesn't matter if it's 90 degrees outside it doesn't matter it doesn't matter. It doesn't matter.

Electric heat 1 watt in 3.41, btus out, it's reliable super simple right: electricity in heat out. No moving parts very simple and it's easy to work on. So that's the good news. What's the bad news? Well, one of the biggest things - and this is the main thing i want you to take away from this when we work in a market which we do where we have a lot of electric heat strips, we need to make sure that we burn them off.

We need to test them at least once a year, and we need to let the customer know that there's going to be some motors, maybe even some smoke in extreme cases, if it hasn't run a really long time when we first test them. So that is an indication to the customer that we've done our maintenance if we do a full maintenance and they first run their heat come december. You know right at christmas time right when we don't want to be working, and we want to be with our families and there's a bunch of stinky smell. What are they going to do? They're going to call us because we were supposed to do the maintenance and we didn't do it properly, so at least burning off the heat strips is critical.

It's very easy to do so. Quick, quick, pull here. What's the very easiest way to burn off heat strips most simple way to remove it from the unit and turn it on and let it burn off on the side yeah. You wouldn't want to do that because if you remove it from the unit and you apply voltage to it, it doesn't have air flow over it, so you will destroy the heat.

Strips heat strips are not designed to run with no blower. In fact they will that's. Why they have these thermal limits and stuff? So if you pulled it out of the unit - and you did power it up it, would they would heat up and they'd go off they'd heat up and they'd go off, so you could do that be fairly dangerous, not the suggested way. I mean you should already be in the air handler, so wr yeah w r.

That's it! You take your white circuit white, low voltage circuit jumper it to your red, low voltage, circuit and heat strips come on. You measure the current on them. You let them burn off for a minute or so and now you're good to go. You make sure they go back off once you take the jumper out.

That's the easiest way! Now. Why isn't that a perfect test? Because you don't know what the thermostat is? Actually, yeah, you don't know if the thermostat's actually calling it on. You don't know if it's actually going to work, but at least you know that they're not going to smell up the place, and at least you know that there's nothing wrong with the strips themselves. So now you've tested the heat strips on the high voltage side, but you haven't tested.

The controls is that okay in some markets - yes in some markets, no right in our market, these trips aren't that critical anyway, and in fact we would probably benefit in many cases by not even having them in terms of people's power bills. So in general, that's going to be a perfectly fine way of testing your key strips, what's a better way to test them. That's not quite the most extreme, but is also a good way yeah at least use single thermostat from the thermostat, but doing it through the thermostat service controls the service menu where you actually go in and you drive on electric heat. So you go into running your second stage heat and then you test it so you're not jumpering it you're telling the thermostat to do it.

You're still not running it under normal conditions, because normal conditions would be to go to the thermostat, set the temperature way up and then wait for the thermostat to turn the heat strips on problem with that is the sun. Some thermostats have built in an algorithm that either uses outdoor temperature like the modern fancy ones. It won't even allow them to come on if the outdoor temperature's high enough and we're going to talk about that or they have a time function. So it has to run a certain amount of time before it's going to let it come on, so you could just be sitting there a long time depending on the settings.

So probably not your best way going into the installer setup or to your installer service setup and just driving on that mode is probably going to be a better way. Ecobee is like the easiest for that. The test equipment, exactly yeah test equipment, also carrier infinity same thing. If you go up and you're doing a maintenance or a service on a carrier, infiniti system just go through into the installer setup and set it into the mode you want it to run in and then that way you can actually test all the different modes very Easily because you actually get a read out too, of a lot of your key readings right from the control, that's kind of kind of nice.

A lot of those are even though even the less fancy than the stats there's an emergency emergency well yeah, but it depends on if emergency heat is actually connected in the way that it's supposed to be with a lot of modern thermostats. That's kind of you put in emergency heat, it calls for w-2, but on older thermostats and we're going to talk about this a lot of times that e isn't actually even hooked up. So it depends on how they're wired these trips are extremely inefficient. So we do not want heat strips to run unless we need them to run, and that's some of the strategies that we use have to have to do with that, so they can cause high bills when they run too much high current can cause electrical damage.

This is another thing, so heat strips are one of the highest current drawing devices in the entire home. There's almost nothing in your home. That's going to draw a continuous - and this is just 5 kilowatt - a continuous 20 amps at 240 volts. That's nothing else in your house draws that much current, which means that nothing else in your house is.

It is important that the electrical connections and the wire sizing and everything is correct. I'm going to pause here. Let that sink in. Not your compressor, not your! Not your dryer, not anything else in your house that electric heat strip is going to be one of the highest, if not the highest.

I said your dr. Your dryer is also a pretty high one, but so that's where electrical connections are really key and one of the big mistakes i see people make one of the things i want to protect you from when you're going in and you're a genius, because you've gotten good With electricity - and you know how to diagnose things, you know how to rig things together when you're dealing with electric heat - and this is also true of gas - furnaces too - they would even be higher on the list - don't go in and start rigging things up without paying Attention to the wire sizing you're using and making sure that those electric heat strips go on when they're supposed to go off when they're supposed to and aren't run through a relay that can't handle that current. That was a complicated sentence that i just used there. The point is: don't run it through some sort of control that can't handle the current and that's easy to do, because it's a lot of current make sense so wire sizing to a system that has heat strips in.

It is going to be one of the most important elements, even if you're say all right. I have a burned up wire inside this unit. Well, i'm just gon na grab a number 14 off my truck and wire it back up. In fact, one of the guys who i worked with at my previous employer before i worked here - he actually got let go because he rewired heat strips with just a roll of number 14 off of his truck, not paying attention to the fact that that obviously isn't Going to handle the current that it was drawing and it ended up creating a little fire inside the unit, which was very problematic, make sense.

So just quick pull 20 amps. What size wire does that need to be typically number 12 wire right? Typically, that's the size wire that you would use now, there's some exceptions to that rule like we talked about in a class that we did recently on wire sizing. But, generally speaking, that's the that's. What we're looking for another common issue is mistakes with blower interlock, so we want to and we're going to talk about how to wire these but blower interlock back kind of what mario was talking about earlier.

We do not want to run our electric key strips if we do not have blower running, and so we have some method to make sure that if the heat strips are running, the blower also runs and that's what we call blower interlock. Sometimes that's done on low voltage, sometimes it's done on high voltage, but it always has to be done in some way, something that makes sure that those heat strips or that the blower runs when the heat strips are on. Why? Why do we need the blower to run when the heat strips are on potential? Fire has a potential fire hazard right, they get very hot, very hot, and so if they keep cycling on and off on and off on and off something gets in there. It could potentially cause a fire and then stress on the electrical surface.

This is another one. So when we go from a gas furnace to a heat pump with heat strips, can we just count on the fact that we can just swap that because hey you got a gas furnace, we're just going to put a heat pump in with these strips? No, we can't count on that. You got a lot of older homes that are running gas. That may have 100 amp service on the house, so you may be able to slam an electrical panel in there.

Well, hey! I can put a new panel in run. Some new wires put a breaker in good to go right, but did you think about the breaker that runs the entire house and the wires that feed the entire house? How often do we think about that with what we do like? Never right, because it's not our! That's not my job right, not my job to worry about that. That's the electrician's job! Well, if we're not calling electrician out to look at it or we're not thinking about it, then we could potentially overload the entire home service, which could be a potentially dangerous problem, especially on older homes that aren't wired very well to begin with. Maybe you have all the old rag wiring or whatever or aluminum wire.

For example, you still have a 100 amp house, where you probably wouldn't put above a 5kw in anyway, but you've seen it look like a 10kw i've seen it yeah and and again we're not qualified to do electrical load calculations, because it's not just as easy as Just adding all the loads up like it's not like that, there's like a whole formula, there's a whole sheet that you have to fill out in order to do that, the point just being that if you go to a house that has 100 amp service on it, This is even 125 and you're pulling a furnace out. Stop ask the question. Look at what's else is in that home and see? Is it going to be potentially a problem because, let's say they already converted a gas dryer to an electric dryer, okay, well, they're right there you've already, you know you've, already kind of screwed up and now you're just going to keep adding to it. Keep adding electric appliances to it.

So it's not always it's not. In many cases, it's not a huge deal to upgrade a service. It's not like the end of the world uh, you know maybe four or five thousand dollars something like that. But you know if that has to be done.

It has to be done before we put our system in, and even inspectors aren't often gon na blow the whistle and have you stop because they're not gon na think about it? It's a change out. They don't think that, oh, you changed out a furnace for a heat pump with heat strips or a stray coil unit with heat strips, make sense cool all right. Let's do some math. This is going to be fun.

Bert's really good. At this now he's an expert at this math right right. Am i right? Am i right? Am i right, or am i right all right? Oh man, all right, so let's do some basic math here. How many watts is a five kilowatt heater all right, so we're going to say it's 5 000 watts right there all right now, this heat strip here see what it says on it.

It says that we are. This is an 8.9 kilowatt heater. So this is not. This is what we call a 9kw right.

If you look at the individual heat strips, these are 4.45 each right. So if we're going to do the math on this, we would have to do it that way, but we're just going to do the math on the board here. So you have 5000 watts we're going to divide it by whatever the rated voltage is for the unit. So let's say that: well, let's look at this one over here.

Look at what we got here. We've got uh, it's got a rating for 208, it's got a rating for 230 and actually it says right here, heater watts. 4600. We would call that a 5 kilowatt heater, but it's actually only a 4600.

kilowatt heater at 230 volts. So it says that right there, 230 4600. So let's do it that way. Instead, that's 208 right! It has both.

So it's got 230. he's just looking at it. Yeah, i'm literally just looking at the tank, so it says right here: 4600, 230, 37.50 at 208.. What just happened there, let's let's stop and address that quickly, so this is only 3750 watts at 208..

Why does the wattage decrease when the voltage decreases? What is voltage correct, amperage is current. What is voltage voltage is potential or electrical pressure, so we're putting more electrical pressure on the circuit right, you put more pressure, you get more current flow or less flow, more pressure, more flow, less pressure, less flow. This is also resistive load, so there's less going on in it, it's more simplistic circuit than a motor. So it's very steady like we talked about you, put one watt equals 3.41 btus all the time all day or day right.

So let's, let's use the math here. If we go to 230, we've got what did i say again: 4600. It's right here on the data tag 4600. So that's what we're going to use we're going to use the one that we've got here: 4 600 watts at 230, volts! Okay! So if the calculation is e equals, i times r, we first have to get our current out of this.

So how do we get our current out of this? Well, we have watts law 2, which is a really simple one, which is watts equals volts times amps. So all we got to do is divide our watts by our volts and it gives us our amps what's interesting about that is. If you look on this data tag over here, it tells you exactly 20 amps if it was 208 to be 18 amps. If we do that, math, that's how it would work all right.

So now, let's figure out how many btus this bad boy produces this particular heater. This is really easy because we already have the watts right. We did the math. This all adds up 20 times.

230 equals 4 600 right. So now what are our btus? So didn't that say: uh 3.41, 3.41 yep. So we take 4 600 watts times 3.41 equals what wait till we get a consensus. 15.

686 right. So that's how many btus we're getting out of it so we're getting somewhere between a ton and a ton and a half of heating capacity out of one five kilowatt heater, which ain't much right. It's a lot to get that much right! How much btus do we get out of 20 amps? Normally on a running system? You know you may have a three ton system, that's giving you that total is drawn 20 amps, but the time you had the compressor the fans transformer everything right. So you can see you're not getting much in terms of btus based on what you're spending here makes sense.

So that's the math! Now, let's go ahead and change one of the variables and see what we get okay, so right now we're matching up exactly with what the data tag says, and so that's handy, it's easy for us. But what happens if we change the voltage? What happens if we change the voltage from 230 to 240., our amtrak is going to go up. Our wattage output is going to go up because we increase the pressure now. The problem is, we cannot do this math.

This way, you're going to be tempted to take this and multiply that times, amps and get watts. But the problem is that the amps also change when i change that we have to go back to ohm's law, okay, and in order to do that, we have to figure out the resistance you're going to notice. Here we don't have the resistance anywhere on this board. We didn't figure out the resistance yet so, let's go back if e equals.

I times, r e is voltage, i is current or amperage and r is resistance in ohms, okay, volts amps ohms. So what do we know? We know in this case that our voltage is 230 divided by 20 equals what 11.5 11.5. So what we know now is that the thing that stays the same or pretty much the same - it actually does change a little bit, but because things actually change in resistance as their temperature changes, but generally they're pretty stable. Now we know that the heat strips are 11.5 and that's the thing that doesn't change.

That's the part, that's not a variable actually right. That makes sense. The resistance of that heat strip doesn't really change, because we can change the voltage which changes. The amperage changes the wattage all that stuff is a moving target, but the resistance isn't a moving target right.

So now we've got to delete amps because amps change when we change volts we're going to delete watts because watts change. We've got to delete all of this. So what are we left with we're left with? Whatever our input voltage is, which we measure so we're going to say that goes up to 240. right e equals i times r.

So we know e 240 equals blank question mark times 11.5. So now we divide 240 by 11.5. What do we come up with 20.86 20.86? What was it before 20. at 230 volts? It was 20..

Now when we increase our voltage to 240, we now get 20.86, and now we can figure out the rest of it again. 20.86 multiply that times 240. What do we get 20.86 times 240. now we're doing watts, law amps times, volts, 5000 and 6..

So now we have a 5k heater before did we have a 5k heater at 230? It was 40 600.. Now at 240, it's over 5000. So it's actually not an insignificant difference. Now we take that we multiply that times.

3.41 equals what oh 17070 it says decimal, but so now that is our btu output. So you're not you're, never going to do this math! Okay, i'm not it's! Not i'm not doing this for the sake of you doing the math i'm doing this so that you can understand what you really have in a heat strip. What you really have is essentially a fixed resistor stays the same. I really had my hand on my hip.

There that was really that was really iffy. It was really really. It was kind of yeah. That's nice um.

You have a fixed resistor and now, depending on the voltage that we apply, that changes the amperage and once we have the amperage and voltage that gives us our wattage, which then gives us our btus, and you can see that 10 volt difference not insignificantly impacted the Amount of btus that we output - if we drop this down to 208, it's going to be a huge drop in the output, make sense everybody get that okay. So that's something to know about these because they're not like a compressor in that way: they're fixed resistance, whereas a compressor or a motor, the resistances vary quite a bit depending on load. These are pretty fixed, all right, so, what's proper wire size to feed an error handler well, the easiest way is just to look at what the data tag says right, it's going to tell you what your mocp is or you're. Sorry, your mca minimum circuit opacity.

It's going to tell you what that is, so you base it on that. You start we're going to typically size our wiring, based on our standard 60 degree celsius, column, which is like you know your safe zone and that's going to be. If you got 30 amps number 10, um, 20, amps number 20, so and so forth. Now, if you have 10 kilowatt heat, that's where it gets tricky, because what do we normally run? What do most people run to a 10 kilowatt heater size? Wire number.

Six is typical, but it is number six 60 amps number six in the 60 degree, column is actually 55, so you have to use slightly better wire in order to be able to use number six. You can't use number six romex in order to do that. So and again, all these charts are readily available. I'm this isn't a wire sizing class we've already done that class, but you know ad nauseam right all right.

So we talked about this. It isn't always 5kw. Just because you see a single heat strip that looks like this don't count on the fact that this is a 5 kilowatt heat strip. It's an individual heat strip, but look at the actual look at the actual strip to tell you what it is or look at the data tag and right here it shows you 4.45 kilowatts at 240, volts on this one, this one's rated at 240..

What was this one rated at on the data tag? 230 right, so it changes it's an interesting thing, because, even even when you look at it's, it's just a silly thing that happens when you look at what it tells you, the breaker size should be what the mca is. Is it telling you what we actually have here in florida? No, it's telling you 230. What do we actually have in florida most commonly? What voltage do you typically see in houses? 45? 245 right? So, what's going to happen to your current on a heat strip, that's running 245! When the data tag says 230., it's going to run higher current, which means what does that mean that the data is that data tag valid now in terms of what size wire? It tells you to put on it. The answer is yes, it is because it's what we got, but it's kind of a goofy thing that manufacturers do sometimes they're going to give you 230 sometimes they're, going to give you 240, but even 240.

Isn't enough? That's why you're going to see uh amperages on your heat strips that are higher than 20 amps? If your voltage is higher your current's going to be higher, your wattage is going to be higher your btu output's, going to be higher all right. Let's talk about some of our different terminal designations. Here letters are a little small on the slide, but so w we see w w just means heat. Does it mean heat strips? No just means heat.

So, generally speaking, w is going to be used on old school furnaces where you only had a single source of heat. It says just w w white, that's heat, bring the furnace on right, w1 means first stage of heat, which could mean in a heat pump. Is what what is first digit heat in a heat pump, carlos first stage of heat in the heat pump? First uh, it's the compressor, yeah, the the compressor with the reversing valve de-energized. Typically, that's first stage of heat w2 is electric heat in a typical single stage heat pump.

But beyond that you know you could have a single. You could have a system that was a straight cool system that had two stages of electric heat and w1 could be one stage and w2 could be both heat strips running simultaneously. So it's not always the same thing and then w3 would be the next stage. And so, if you have a you know two stages of electric heat on top of a single stage, heat pump, then w3 would be your second stage electric key, but you could also have a system that has two stages of compression like a two-stage compressor.

W1 would be first stage. Compressor w2 would be second stage. Compressor w3 would be heat strips that's why, when you had, when two stage compressors first came out, we had to use uh two stage: cool three stage: heat thermostats. That was a really big deal to find them that were that way, they weren't wearing a lot of the maid.

The old honeywell chronotherm back in the day was one of the first kind of fancy thermostats and you had to had to get the one that had the three stages of heat in it, because you know first stage is first stage compression. You get what i'm saying so and then emergency heat is usually just a way to manually drive on your backup form of heat. It really is not ideal for heat pump markets where you only have five kilowatt heat, because what it does is it locks out your heat pump mode and it only drives the electric heat which usually isn't going to do much of anything. You know if it's 20 degrees outside.

Do you think this little 17 000 btus is going to do much to heat a house? No, it's going to do very little to heat a house. So it's i mean it's better than nothing. I guess, but generally speaking, we're not going to use emergency heat much in a market where you have very large heat strips or in a market where one of your stages of backup heat is actually a gas furnace. Well now that makes perfect sense, because there are markets, they call it.

You know hybrid heat or whatever, where you actually run the heat pump when the temperatures allow for it, and then you get to a certain point and you run the gut. You shut the heat pump off, you run the gas furnace, and in that case, if your heat pump's failed, you put in emergency heat, so it just runs the gas furnace that makes perfect sense right, make sense cool. This illustration shows kind of an early way that we used to wire up thermostats, where we would actually have to always jumper aux and e or w2 and e together. We'd have to actually put a physical jumper in there used to be a lot of physical jump.

Ring in many cases old thermostats, you would even have to jumper y1 and w1. Together we're going to pause here, because i see you falling asleep, older, thermostats, y1 and w1. We would actually jump her together. Why would we do that on some older thermostats? What do you think function, because if it's a heat pump, y1 and w1 are the same right? What does a heat pump do when you need to run first stage heat it calls y with no reversing valve? What does it do when it runs first stage cooling? It calls y with a reversing valve right, so in older thermostats you didn't used to have an installer set up we're used to this.

Now as a standard thing, every thermostat has an installer set up. You go in you tell it what kind of equipment it is, but on older thermostats, all the way back to mercury bulb thermostats, which are actually the standard. When i started in the trade, not that long ago, in 2000, people had mercury above thermostats everywhere. Isn't that wild kind of throws me off doesn't seem like 2000 should have been should be 21 years ago, but it was um yeah.

So in those types of thermostats you didn't have internal logic. So the only way you could tell it what kind of system it was was by putting jumpers in place and you'll still see. Some of these you'll actually have physical jumpers in place, and so you had to jumper uh y1 to w1. Nowadays, you tell the thermostat that is a heat pump and it automatically does that it automatically just energizes y in both heat and cool testing heat strip, current.

So 5, kilowatts, it's about 20 amps, but we talked about why it changes if you're hooked up like we are here, because this is a 208 facility, quick question: why is this a 208 facility? What does it mean for something to be 208 say it again? It's going to be generally commercial commercial, but why are commercial buildings off in 208? Why is that? Because if i measure, if i measure the outlets here, what voltage am i going to get out of these outlets you're going to get 120 right? But it's three-phase right and so you're going to get 120 on these yeah yeah? No, you get 120 still because from leg to neutral, it's the same. It's from leg to leg. The two legs are no longer uh 180 degrees out of phase like they once were so 180 degrees out of phase means that they're, you know like this. It would be, what would it be if it would, if it's thirds it would be 90 uh? Why am i all of a sudden having uh be like this 120 degrees out of face yeah wow? That was really weird, so so, because they're not because they're not the faces, aren't lined up now you have a lower voltage between phases.

So that's why you have two way, the point being that you're gon na see 208 when the building is a three-phase building and you're only using two legs and that's what this is. This is single-phase equipment hooked up to two legs of three-phase. So when that happens, you're gon na see lower output, which means you're gon na see lower current. So just because you were to measure you know 18 amps on this, you wouldn't because you might think.

Oh, this heat strip's not working properly. No, it's just that the input voltage is lower, so input load, input voltage, lower equals lower output. Lower current 10. Kilowatts is around 40 amps, but it's still 20 amps per strip.

So if you imagine this was this is 10kw. This is actually a 9kw strip, but if it was a 10kw strip, you'd have five and five, so you could still measure them individually. You put your amp clamp on the black wire that feeds the strips one side of the strips put. Your clamp on it'd be 20 each.

If you went to the main leg that feeds it, your main input or you put it under both wires at once. Then you would measure 40., make sense cool, but it's still going to generally be maximum of 5 kilowatts per strip, and this is just showing this. So if you look a nap draw on both here at once, yep as long as you're, not opposite phases, they're on the same phase, then you'll measure the same, and these would be if you took both blacks and put a clamp over both you'd measure. The cumulative amount, so this guy right here, what is this 5 kilowatt or 10 kilowatt it? Actually that was a trick question, because this is the same one.

We just looked at, it's actually nine, but it's two separate strips so yeah. It says it right there. This one right here is this: a 10 kilowatt or a 5.. It's a 10.! You see two separate strips right this guy right here.

You can tell it's a five, because there's only one it's in the center, that's a five! Now it isn't necessarily what i'm saying this: that could be a 3.5 it's, but it's a single strip, all right heat strip, thermal limits, i'm going to pass this bad boy around. So you can take a look at the thermal limits, this one's interesting, because it's got thermal limits, thermodiscs on the high voltage side on each strip, and then it also has a low voltage thermodisc too, which also protects it. So it's got double double the protection. Huh pass it around.

It's fun we're having a good time here, everybody's enjoying themselves. You know um! So if you look at oh that's right, he was in the last class. Wasn't he he was in your uh hashtag class yeah hashtag class yeah that other class that happened a couple different types here: we've got a fusible link, which i want to mention quickly, because you will see these. Sometimes this is a single.

This is a single fail. Um, so is the one with the orange wires thermal overload this one here is that's what eric told me he what why he says he's pretty sure it's a single fail. I don't think so. There's a button right in the middle of it.

You can click it. No, i didn't just reset it, but if there's not then auto reset, i still think it's not a reset, but whatever the other thing you're going to notice here is they actually have temperature ratings right on them, so 150 degrees, and then it resets at 55 degrees. Less than that is what i think, that means not that that really matters that much this got this little guy. Here's 180 degree trip, so you can, if you pay attention you'll notice, a lot of interesting information, but if you see one of these, and one of these is open, you have to replace it now.

How would you know if one of these is open or any of these? How would you know if they're open, open out be the easiest way right so take the wires off? Take your own meter obviously shut the power off first measure across it. What are you going to measure if it's open? Oh well, infinite, ohms, no path! Right! If it's closed, maybe if your meter has that setting on it but a lot of times, i see text, don't have their meter on there like it's, not ringing out and as you look down the meter, it's reading zero right or point one or something like that. Look it's reading point one. Is that good or bad low ohms means good path? Infinite, ohms means bad path.

Infinite almost means open, low ohms means closed right. All these are switches, so they don't consume energy. They just open and close in order to protect the circuit. All right, what can we use to control a heat strip, the top the two top ones? Here we show a heat sequencer and we show a contactor.

So when we talk about control, i'm talking about the actual line voltage control, what actually turns the heat strips on and off? There are certain types of i'm telling you it's the thermostat or something's wrong. So you have uh relays or they actually wouldn't call them relays. They would call it a contactor um that are rated for the current that a heat strip uses come on in have a seat come on in come on in come on in it's okay, it's good we're. Having a good time um you have contactors.

Some brands will use a big old contactor in there to turn it on and off, and some will use what's called a sequencer or sequencing relay. The only thing to know about a sequencer that makes it different. Is that a sequencer, the contacts close at different times, because it actually uses a heater so rather than an electromagnet down here it has a heater and that heat causes these little round thermodiscs to snap at different times in order to make or break the circuits. So, basically, when you see a sequencer, it's generally there, because you're running things at a different sequence, you talked to them bert yeah.

That might be just disrespectful right right. It could be just a few seconds. It doesn't all come on at once could be, or it could be so that you have a fan off or on delay too. So you get the point.

So sequencer brings things on at potentially different times and they're generally designed to handle the current that a heat strip is going to have and again depends on what type of sequencer it is. But what you don't want to use to control heat strips line duty is a regular relay like a 93 40 or 93 80.. So quick pause, yeah, quick pause, i'm just going to address this again. Why do you not use a 9340 or 9380 to directly control the line voltage of a heat strip? Why it can't handle the amperage can't handle it? You know it can't handle the heat, so it needs to get out the kitchen.

Am i right? It's like tom cruise from a few good men. It cannot handle the truth. You know what i'm saying all right: 15 amps, that's all it can handle 15 amps. So if it were a three kilowatt heater, it could maybe barely handle it, but that's not what we're gon na.

That's not what we're gon na use for that. So this is for uh fans, blowers, condenser fans, that sort of thing and then controls isolation, whatever it's not for heat strips, but what's interesting is we actually use it in conjunction with heat strips for a fan interlock sometimes - and this is where it gets a little Tricky and they may not always use a 9340 but they're going to use some sort of similar control, we're going to talk about that in a second all right, let's talk about heat strip staging. Why would we stage heat strips if you had more than one so that way they don't come on at the same time, you're especially going to see this in other markets where they have 15 and 20 kilowatt heat less current yeah? That's it's brilliant, brilliant where'd! You get that from what else. What else there's one other thing: um, the less electric, the better, the better yeah? It's a good! You make a good point, less electric heat, the better.

So if you only need five kilowatts in order to keep up, then only run five kilowatts and let the heat pump do the rest right, because the heat pump is far more efficient than the electric heat. The other reason is, if you bring on 20 kilowatts of electric heat, all at once. How much current is that it's not hard math. 20.

20. 20. 20. 80.

people count on their fingers. Pull off your shoes use your toes 80 amps, 80 amps, all at once. Amps, all at once, i was struggling with that yeah and again i mean whether you run 80 amps all at once, or you run it slowly. It's not it's not like it's that big of a difference, but if you don't need 80 amps, it comes down to the staging.

If you don't need it, then don't run it. Basically, if it were 20 kilowatt. Any questions about that. I said we're only going to go an hour already over an hour, so i'm going to finish up this class and we're just gon na leave all right how's.

That sound sounds fun to me. I like going home. Where did you get that diagram? That is so nice yeah sure is it's right in my site, if you, google, 9340 or any of this stuff, you know i have a website. It's got some good resources on it.

It's a great place to prepare if you're going to give a class last class. Okay, so um, this just illustrates oh boy, some money, somebody's gon na get it ballsy you'll notice that these two actually kind of look the same. So this shows the coil. So that's these points here.

So that's actually the electromagnet that switches its position. This is the normal position normally closed between one and two normally open between one and three and you'll see they have this same diagram drawn on here. That's this guy right here, one and two are closed. One and three are open right.

If you energize it. What happens from here to here? It goes open from here to here. It goes closed so and this guy same thing same same time, make sense, yep all right cool. So here's how interlock is wired, we're just going to talk through this circuit very quickly and then i'll show you how to think about this circuit.

If you ever have to wire it, because it's a it's an opportunity for a big mistake. If we wire up this interlock in such a way that the heat strip current is being carried through, the relay we're going to melt the relay and make a big fire right - big stinky plasticky mess. So we don't want to do that. We have to make sure that it's set up in such a way again back up.

What's the purpose of the interlock again, anybody remember make sure the fan comes off. Blower comes on with the heat strips he strips her on blowers on. At the same time, that's the reason that it's there now again they're not always going to look like this relay, but the interlock's almost always going to be wired. If it's line voltage, it's almost always going to be wired in this same general way.

We don't want every time the blower is on for the heat strips to come on right. That would be bad, there's a lot of ways you could wire it so that every time the blower comes on the heat strips come on. That would be easy to do to make them both come on at the same time, but we don't want that. That would because very high power bills right, don't want that.

We also don't want the heat strip current to be carried through any of these contacts. Kind of tricky, so here's how this works, and this shows the terminal numbers on it. So if the heat strips go on, so this contact for the heat strip closes both of these clothes right. Imagine these clothes you have voltage coming through here.

This relay is already regardless of whether the blower was previously calling is closed, which brings on the fan right current for the heat strips isn't being isn't being taken through any of these, let's say that the that this relay is already on, so the blower was already On well does that hurt anything? No, because the blower is already on these clothes. It doesn't make it through to the blower, but the blower is already on so who cares right either way if these heat strips are on, the blower is also going to be on. So, rather than your heat, your blower relay back feeding your heat strips your heat strip relay is back feeding your blower through a relay that prevents the opposite from occurring right. We don't want every time your blower is on, for your heat stress to be fed.

So, let's look at it the other way. Let's say that we have our. You know we have a g call so when it calls on this closes - and this opens for our blower to run right so now our blower is running. Can it back feed our heat? Strips nope, because this is now open because you have a g call right, so you get this.

This is when you don't have a g call.

37 thoughts on “Electric heat troubleshooting, service, and math class”
  1. Avataaar/Circle Created with python_avatars Brian Mcdermott says:

    Great class Bryan. Thanks for your time.

  2. Avataaar/Circle Created with python_avatars H-H Hidalgo says:

    Great class Service area Barrhaven??

  3. Avataaar/Circle Created with python_avatars Mr Green says:

    Is it best to have the blower on low speed or medium speed for electric heat? Would that depend on the size of the heat kit?

  4. Avataaar/Circle Created with python_avatars Joseph Jorgensen says:

    Why don't hvac just run a click plc and program all these steps the trouble shooting becomes so easy

  5. Avataaar/Circle Created with python_avatars Terry Graham says:

    You should have measured the ohms on the piece of strip you cut off and then added a resistor to make up for it. lol…so easy!

  6. Avataaar/Circle Created with python_avatars DakotaB says:

    Boogie-woogie-woogie lmao

  7. Avataaar/Circle Created with python_avatars Afif Jebara says:

    An amazing guy, an amazing teacher. Honesty, integrity and competence Thank you Brian! Are you in Kanata ?

  8. Avataaar/Circle Created with python_avatars John D says:

    3 phase heat strips are a way different animal. I cant wrap my mind around how their wired.

  9. Avataaar/Circle Created with python_avatars John D says:

    We use to have installers leave the instruction manuels inside the heat strip section of Air Handlers. First time the heat strips came on, instant fire, smoke and plastic melting.

  10. Avataaar/Circle Created with python_avatars Robert Gray says:

    Show a video on fan poeer box Are you in Nepean ?

  11. Avataaar/Circle Created with python_avatars AVIIDIX says:

    Im completing electrical engineering programs in school right now and these lessons are way better to learn and understand what's actually going on. Great lessons keep up the great work!

  12. Avataaar/Circle Created with python_avatars Walter Brown says:

    Re. your first chart: Another benefit of electric heat is the fact that it's efficiency is 100 % from the standpoint of energy conversion from electric to thermal energy. (You can probably win a few "Bar Bets" on this one) Are you in Barrhaven ?

  13. Avataaar/Circle Created with python_avatars Frank Roper says:

    It's good to know the ohms of what you are working on since you can't always jump red to white…the reason is in some old buildings they have used whatever color wire they had on hand to wire a thermostat and you have to know the ohms of what you are working on and then ohm out the circuit to the common wire until you find the right circuit. It is not a perfect world like in a classroom when you get out in public! They jump stuff and then you have go in and try to figure what they did so you can get to the root cause to begin with.

  14. Avataaar/Circle Created with python_avatars Frank Roper says:

    They call the fire dept and say they smell smoke sometime!

  15. Avataaar/Circle Created with python_avatars Gene Williams says:

    In the old days if you jumped r to w you could burn up the heater anticipatory

  16. Avataaar/Circle Created with python_avatars Gotchaplumber Gotchahvac says:

    Bryan: another good, informative video!

  17. Avataaar/Circle Created with python_avatars sd sd says:

    Great lesson. Got a question on those same heaters in the box there's the small sticker u showed in the video and then there's 2 big stickers with the different model of AH on the big stickers it will be 208/240 volts and the MOCP is different compare to the smaller sticker that rating is at 208/230 volts so my question is should we used the MOCP from the big sticker? as its 208/240 since when we measure voltage its usually a little over 240v.

  18. Avataaar/Circle Created with python_avatars ED BELLE says:

    I respect the fact that you admit to your past mistakes. Lot's of seasoned techs pretend they have never made a mistake to the newer techs.. Good deal!!!!

  19. Avataaar/Circle Created with python_avatars Random Robby says:

    Y is going to be first stage of heat in a heat pump W1 would be second stage

  20. Avataaar/Circle Created with python_avatars michael sidote says:

    Electric stoves, and spas draw 50 amps on 220.

  21. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    Thanks again for the videos!
    Stay safe.
    Retired (werk'n)keyboard super tech. Wear your safety glasses!

  22. Avataaar/Circle Created with python_avatars RV10flyer says:

    You can measure Voltage across those switches with power on. If you see “0” you’ll know it’s good. Be careful not to short out and burn up your test leads. 🤚

  23. Avataaar/Circle Created with python_avatars RV10flyer says:

    I only use 10 ga THHN wire, quality 10 ga terminals and a ratcheting crimper. Most of those electrical compartments do not have enough air movement to keep wires and terminals cool. No more overheating issues near the terminals.

  24. Avataaar/Circle Created with python_avatars RV10flyer says:

    Your water heater and dryer both pull over 20A at 240V. Service area Ottawa??

  25. Avataaar/Circle Created with python_avatars dustin741 says:

    Awesome video, thank you.

  26. Avataaar/Circle Created with python_avatars JJ 109 says:

    Very good video…

    Hybrid heat is actually called Dual Fuel … This is important cause you CAN NOT use a heat pump compatible thermostat.. It must have a Dual Fuel compatible thermostat to run a dual fuel system which utilizes a outdoor temperature sensor for you switch over ( balance point)…..

  27. Avataaar/Circle Created with python_avatars john doe says:

    Heat strips are no bueno amigo makes bills 💵 too high great video hefe

  28. Avataaar/Circle Created with python_avatars Tom Thumb says:

    You still have an issue with the defrost thermostat as wired.
    If you do not run a wire to the air handler, how does "E" work on its own?
    Maybe in FL is is not an issue, but in the northern climates and the customer has a heat pump issue, how would the "E" be energized?

    We have that code for any energy rebate from the power company. If they come out to check on their random inspection, it will not pass and the owner won't get the rebate until it is fixed.

  29. Avataaar/Circle Created with python_avatars Captain Price says:

    Thanks for school though. I needed a refresher

  30. Avataaar/Circle Created with python_avatars Captain Price says:

    Time delay usually takes 5 minutes..

  31. Avataaar/Circle Created with python_avatars Whitney Owen says:

    Amazing content!

  32. Avataaar/Circle Created with python_avatars Jericosha says:

    Thank you so much for sharing these and willing to be vulnerable. You guys are a blessing to techs that are seeking to better themselves. Service area Orleans??

  33. Avataaar/Circle Created with python_avatars AZ Aztec says:

    Best intro ever 🤣

  34. Avataaar/Circle Created with python_avatars clem says:

    Aonther reason I love hvac school your stories add some dad jokes next time lol

  35. Avataaar/Circle Created with python_avatars Akroppoli says:

    😁 thank you

  36. Avataaar/Circle Created with python_avatars Ganesh Kathayat says:


  37. Avataaar/Circle Created with python_avatars Tawfik Tawil says:

    Great we need this

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