The free training provided by the HVAC school podcast is made possible because of the generous support from our sponsors, testo rector seal and carrier. Alright, if you guys have listened to this podcast for any amount of time, you know that I kind of have a little bit of a crush on the testo 605. I it's just a stupendous, can I say stupendous and not have it seem like hyperbole, I'm gon na choose to say stupendous. It is a stupendous tool for the investment that you spend on it.

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As long as you move to the CFM s, which is pretty cool CFM, I always want to say CFM's CFM how they're so the 605 eye is a great tool. But when you add in what Jim Bergman is doing with a measure, quick app, which you can find out more about going to measure quick, comm, four slash download now on that application, you know I'm excited about that product, but the test of smart probes in this Test is 6:05. I work with Jim Bergman's measure, quick app, and so you can get the best of both worlds. A really really highly functional, app plus the test of 6:05 is that the actual smart probe app that you can use directly with a 605.

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This is the podcast that helps remind you of things that you might have forgotten about. The hvac, our trade, or maybe reminds you of some things you forgot to know in the first place, and today's episode is about history of gas, furnaces introduction to the history of gas, furnaces which chums very intellectual. But the fact is is that it's actually very practical and of course, whenever we have Jim Bergman on, you know, he's gon na bring it, and you know he's gon na embarrass me, and this episode is no exception to that rule. So we go through all the way from old gas will actually start with wood-fired appliances and Jim takes us all the way up through the modern modulating high-efficiency furnace of today, and just all everything in between and all the safety and just the different kind of the Idea behind why these changes have happened in gas furnaces and gives you a really good kind of basis and then, in future episodes to talk about combustion.

Analysis. We're gon na talk about the diagnosis and sequence of operation of different types of furnaces and we're going to talk about the proper commissioning of gas furnaces all with Jim Bergman over the next several months. But this is a great episode hope you enjoy here. We go Jim Bergman, the history of gas furnaces, I'm here with Jim Bergman, Jim, it's been almost a month since you've been on the podcast.

My numbers have been diving. I was thinking about just closing up shop and just saying forget it. If I couldn't get you on so I had to beg and plead it was the best month of my life. I mean I really can't complain too much not having to talk to you is it made me feel a lot better about things, so it was refreshing.

Yeah I need, but then you had the need to have a conversation with somebody in which you could dominate 95 % of the conversation. So here we are yeah. I guess my wife's gone this weekend, so I got to talk to you and it's true. I'm sorry, and actually today is gon na be worse than usual, because, unlike some of the other topics that we've talked about, there's even a greater gap in experience between you and I on this topic than even some of the others.

So today we're going to be talking about an introduction to furnaces and I've probably worked on a thousand furnaces in my career, but mostly it's been just regular maintenance and stuff. They don't really break that much in Florida because I don't run them very much. Let's start by going through wherever you like to start when you're talking about furnaces, introducing them to somebody who maybe doesn't know that much about furnaces. I actually like when I would go through this with students.

We talked a little bit about each type of furnace and when I was teaching a high school program and actually learned quite a bit of all the way because you get into this stuff, you don't realize the long history we have a user natural gas for gas Heating, which goes probably back into the nineteen, maybe even then late, 1800s, 1930s or so we're, probably when it was really in its heyday, 1900 and 1930, and everybody had coal furnaces and then all of a sudden natural gas became a little bit more readily available. He switched from burnin, wouldn't coal to natural gas and up here well, we're at you still run across quite a few homes with coal chutes in the basement, where they used to have a small door that somebody could open up and they could dump a big ol Pile of coal in your basement, while you're at work or whatever and all the heat was delivered by truck back then. So it was a whole different ballgame. But it's an interesting part of our history.

It leads into a lot of interesting things with gas furnaces that probably some people here have never even thought about before, because when we first got into gas furnaces, it was actually about modifying the existing coal furnaces. We have and putting a new fuel and you've done understand it. It leads to a lot of confusion, especially when you start looking at a gas flame. The first question: Brian I'm, going to ask you because of your huge knowledge of gas furnaces working on a lifetime.

What I've worked on in a heating season, maybe up here in the north, what colors for the gas flame B? Well, I'm gon na go ahead and answer what I've always known to be true and there's no way you can convince me otherwise, Jim, because I know so much about it and that would be a nice pretty blue flame. It's what we want to see. That's actually what I would think too, but the gas flame being blue is actually a modern thing and if you get into some of these older furnaces and think that's real important for especially you guys that work up in a northern climates here and run across the Old 20th century and Weizhou gravity furnaces, and things like that, a blue flame will actually be about the worst thing you could have in that furnace. A completely robbing of efficiency - and let's talk about why that is because it's fairly interesting, I think it all goes back to understanding.

First of all, how furnace burners and how furnaces work. I mean we had basically this big old pot that we would put coal in and we have a fire going in there. A big flame in there heating up the inside of that pot and it's real important to understand how the heat transferred in that, because these were like really simple designs and when we think about heat transfer, we've got to always think about heat transfer from the flame. To the heat exchanger and then from the heat exchanger to the room, it comes down to well.

How were they transferring heat back then? Well, if you think about this real, simple design, we talked about probably transfer heat, conduction, convection and radiation, and radiation heat transfer like the Sun. Conduction means that we're actually heating it up heating, the metal with a flame directly and conducting to the surface, and then we have convection which were moving heat from the flame through a complex heat, exchanger design and as the hot gases scrub. The walls of the heat exchanger, it liberate the heat. When you looked at old furnace, they really did not have complex heat, exchanger design.

You had a fire inside and that basically went through a single pass or maybe a double pass. Heat exchanger then exhausted outside, which would result in theoretically, all your heat going up to the chimney. Well, the question is: why didn't it, what was the method of heat transfer and when you look at these old gas furnaces and you look inside you'll - see that a lot of them had a bright orange flame and that bright orange flame was called carbon luminous flame And it actually was bright orange, just like the Sun. In fact, it's a good reason.

The Sun is orange because it's designed that way to transfer massive amounts of heat energy by what method Brian radiation, Jim radiation yeah. So if the Sun was blue, they wouldn't transmit any heat at all by radiation. It'd be a very poor conductor of heat to the earth, but it's not it's orange, and when we look at a gas flame and an old furnace, it has to be the same way because the primary heat method of transfer was by radiation. And this is a good way to understand this is: have you ever written ox, acetylene torch Brian.

I have I've done that a time or two my career, some guys only used those turbo torches. I wanted to make sure you weren't completely lame and you actually understood what an axis suddenly torch was. But when you like the acetylene, what do you feel right away when you like this suddenly in first well? The first thing I feel is shame because I'm letting little carbon bunnies go all over the customers house, but the second thing I feel is heat. You feel massive amounts of heat right and then, when you dial in the oxygen we know for a fact the flame gets hotter.

But what do you notice goes away? You know it's hotter, but you don't feel as much heat coming off of it. You don't feel that radiant heat, you don't feel any heat anymore, you all it's, because it's a smaller flame, you don't feel any heat. That would seem to make sense, but actually that smaller flame is much much hotter. So, in fact, it is giving off a tremendous amount, more heat now that we've mixed oxygen with the acetylene, but we don't feel it anymore and that's because the heat now is the color.

The flame has changed and the heat transfer by radiation has effectively stopped. So when we're looking at an oil furnace or in a gas furnace like especially old fuel oil, too, you look inside there. You see that the flame is bright, orange and again that's a carbon luminous flame in an oil, carbon luminous, flame and gas. Furnaces are required.

So that they can actually transmit the heat energy from the flame to the heat, exchanger surfaces, and if you were to install a retrofit burner into a gas furnace or into an old furnace with a bright blue flame, it would actually almost stop transferring heat altogether. All the heat would go up, the chimney and efficiency would go into the toilet and that's exactly what we saw a lot when people were putting these gas burners in to retrofit equipment, and so the color of a flame is very dependent upon the design of the Furnace and for modern furnaces now we did some things that are interesting. I want to express a couple of things here that I think are really important. A carbon luminous flame, if it's burning correctly all it means, is that the carbon molecules are actually burning in the air.

Just like those dustbunnies, you have that's carbon, that's unburned carbon in that acetylene torch. If we were to burn that carbon burn that dust bunny, it would glow bright orange and that's exactly what's happening. But it's all inside the flame and if we're completely burning all that gas up by radiation, we are going to have a fairly good combustion efficiency. And typically, when we're talking about burning fuel, we want to consume all the fuel that's going through the appliance, and so when we're combustion testing.

What's really interesting is if you combustion tested a furnace from 1930 and a furnace from 1980 and a new 97 % efficient furnace in the net efficiency. They would all be about the same that all be around 80 % combustion efficiency. If you looked at basically how effectively we're burning the gas, what changes with these furnaces, we'll get into newer furnaces, is actually how we utilize the heat that we're producing. So when you look at combustion analyzer, it's actually not analyzing the combustion process.

When you look at the efficiency number, it's actually a modified equation that takes into account not only the combustion efficiency but also an Associated stack losses. So it's a hybrid equation. It's really not truly combustion efficiency, calculator, its combustion efficiency and stack losses and stack causes. Are those that are heat going the chimney and then also excess air? So when we look at that a couple of things in port, but it's a little bit of a sidebar we'll get the next one on combustion efficiency.

But when you look at this, the older furnaces, an orange flame in there is actually desirable and you can produce an orange flame without producing any carbon monoxide in the flue. Because, again, if all that carbon is consumed in the carbon luminous flame, then all it's going to come out of the stack is carbon dioxide, water, vapor and heat. So that's why sometimes you look in there and the reason I think this is such an important part. To start with is the guy is a look inside of a furnace.

I go all the flame is yellow and it's not burning right now go and they'll shove. The combustion analyzer and a probe - and I go - how am I not getting any carbon monoxide, this thing's, these yellow, as could be, and it's actually a yellow gold orange color - is what is ideal. It's not like a starved flame, which is a little bit different, color or yellow, but they're. Looking at it.

They don't know what it is assume it's burning poorly and they consume. It's got poor combustion efficiency, but in reality, it's burning safely and it's burning exactly the way it's engineered to burn in that old appliance. The older ones were heat transfer by radiation around 1970 right, because you got to remember to let me go back and look at this stuff. We first designed furnaces think about what we're burning, we're, burning, wood and we're burning coal and the flame was in contact with the metal.

We had an pinja meant the outside surfaces would get really hot, so we really needed this really heavy-duty heat exchanger and a lot of heat exchangers were made out of cast iron and in fact, furnaces used to take three to four days, sometimes to install, because a Guy had poor pad on the basement floor he had to haul down cast iron pieces, some of which weighed 2 or 300 pounds apiece. Some of the cast iron pieces weight up upwards of 700 pounds and some of the big old furnaces on there. They had to assemble every one of those pieces, they had to put gas getting in between it and they had to bolt them all together, and then they had to put fire cement on in between sections, and it was a huge project to put a furnace in Your house I mean it was a big expense. It was heavy duty.

These things are last forever and we used to say well now we're looking to go. They up we're in fishing, but they were really quite efficient for their time and like right now with Caspian. So cheap, I think, we're at three dollars and mcf. You get to the point where you're wondering how fast the paybacks gon na be.

That again is another discussion, but it's interesting when you look at efficiency and gas furnaces back, then it was a big job to put these furnaces in and big pieces of, cast iron that we had a thing took forever to heat up once it got hot. It would tend to stay hot, the old furnaces didn't even have a blower and I'm they heated by gravity, cold air would fall and warmer would rise because it was less dense so and he had that real heavy cast-iron heat exchanger. So I could get up to really high temperatures. Typically around the limits were set at 225 degrees, 250 degrees and the thing cranked out pretty warmer air and kept your house pretty comfortable.

Now, obviously, there's a couple of things that you also got to realize we're on this old furnace. First and foremost, is the draft hood well look at how that furnace exhausted. That's really important to understand what the draft it is forward. Do you ever think about that? Brian, you know what the graft is for.

We don't have draft hoods in Florida. That's not something that exists. So tell me more well. Do you have pool heaters in Florida right now, yeah? Okay, all right! You got me, you got me yeah.

We do have two liters. I don't have to come to Florida to tell you what you don't know. Oh my gosh, all right all right. So what is the draft hood for on a pool heater? The draft hood is to actually introduce air into the flue hay and actually you know I'm not really clear on exactly what goes on.

I know it cools the flue gases. At least my understanding is that it regulates the flow through the burner. Am I on the right track here I'll keep going. This will provide some entertainment for everybody, I'm not saying, in other words, I'm editing it all out, so nobody's ever gon na hear this.

No, no! It was really good. It was really good because what you said is what everybody thinks that drafted is for and okay, that is completely wrong. Okay, the function of the draft hood is to separate the appliance from the draft okay. Why would you want to do that? Hmm? Well, let's think for just a minute what happened so in order for air to come into a furnace in order for air combustion air to come in what has to happen now.

There's two airs that going to furnace obviously talk about that for a minute. We've got primary here and secondary here, primary air being the air that goes through the burner that is induced by the venturi effect, because we're shooting a stream of gas in there and the gas and trains air and then well-designed venturi. The proportion of air is proportional to the gas, so as you raise or increase the gas pressure, the amount of air that we pull into the burner also raises or decreases now, when we look at secondary air in a furnace secondary years, the air that goes around The flame and it's pulled in around the heat exchanger Inlet, so we know that primary air gets into the burner through the gas firing into the orifice. How the secondary air get in in most of my modern experience is because you have some form of forced induction, where it's actually drawing it through with the pressurized inducer fan least that's what we call it in Florida, and we don't have that in a pool heater In a pool heater how to secondary air get in, we have those in some pool heaters as well, but we're gon na say a natural draft pool heater it's drawn in because you're increasing the temperature.

So as you increase the temperature, hot air rises and it escapes, and it brings air in behind it and creates a low pressure and high pressure environment that draws air in so the heat of the flame is what creates the draft. Basically, it pulls in to the bottom right now. Let me ask you a question: was he ever seen a movie backdraft Kevin going back to eighties? Oh, my gosh, you haven't seen them that's when I was born so uh, yeah, okay, the whole premise behind a backdraft is that these firefighters they're fighting these fires and every time they open up doors, the flames burst out and burn everybody to crisp, because the flame Is looking for oxygen right so when we take a gas furnace and we block the flue pipe and there's a flame in there if the flame can't get air through natural, rising the heat rising to the heat exchanger, because now we've blocked that off. If no air can come in, what do you think the flame is trying to do it's gon na jump back out at you? It's gon na roll out, it's gon na roll out yeah because it's looking for oxygen and it can't get any air and hence that's what the rollout switches were for on modern furnaces when the gas way becomes completely plugged the flames come back out the other side That was engineered to shut the furnace off now.

Back in the day, we didn't have rollout switches on modern furnaces, so what we did is we had a draft and the draft diverter was designed to disconnect the chimney, the flue from the furnace, because, if a raccoon crawled down your chimney or something crawled down your Chimney and car dead well, we would want the flue gases to escape into the basement. You know flue gases in the basement. This doesn't sound good, but what are byproducts of combustion of good combustion? What are they do? You know off the top. Your head? No go ahead.

Byproducts of safe combustion are carbon dioxide, water, vapor and heat. That's it all. The carbon in the fuel is converted to carbon dioxide. Well, we have an intermediate conversion.

Other words like it doesn't all completely convert we get carbon monoxide and carbon monoxide is dangerous to humans, because, basically, your blood can't tell the difference between oxygen and carbon monoxide and you just die from oxygen deprivation. That's what all this is about when your blood replaces all the o2 with Co. You die a slow, painful death which probably most people don't want to do so we try and avoid that, but back in the day we would exhaust all the flue gases into the basement. In fact, I've run across hundreds of furnaces over my career that are exhausting flue gases in the basement and you go well.

That's got to be obscenely dangerous and yeah. It is dangerous because if the furnace were to make carbon monoxide we'd be exhausting carbon monoxide in the house, which is really bad, but most furnaces back in a day if they were gon na hurt somebody do you have any idea how they hurt people. It wasn't through carbon monoxide poisoning, I'm super burning, the building down. It was burning the building down a hundred percent correct, I'm glad you got one Brian.

I think this is the second one I've gotten so far. I don't have a great record, so yeah burning the building down back then we used to have firefighters and they had watchtowers and homes burned down. Quite a bit because appliances just weren't safe, we used a lot of wood. We used a lot of coal, then we converted to gas and if we blocked that chimney off and the gas flame was coming out the front looking for air, then it would catch on fire.

Whatever was next to it. In the basement, again, diverter was put on to protect the consumer from their house burning down and it was assumed that if we had good combustion, the only thing we debate you know the base would be carbon dioxide, water, vapor and heat, and so overall that's what That draft hood is for, and the other thing is, is that when we look at the draft hood and we look at the furnace and it's running it exhausted the exact amount of gas and air that it needed to pull in the amount of air it needed. For combustion, in other words, whatever goes in, is also what comes out right, and so the natural draft of the appliance would pull in an exact amount of air that it needed and it would have come out the other side as carbon dioxide, water, vapor and heat, And so the older furnaces, if you measure in before the draft inverter, in other words you get up inside the cell, the heat exchanger you'll see that those older furnaces run around 20 percent excess air. What that means is excess air means that air that was not used in the combustion process, so the furnace is actually supplied with 20 % more air than it needs to burn all the fuel.

That's in there and excess air is a necessary evil, but it's also a big energy waster when it comes to an appliance - and this is one of the reasons we eliminated the draft hood - because let's talk about this for just a second for every one cubic foot Of gas that are burned, you need primary air and you need secondary air and overall there's about 15 foot of air that are used as primary and secondary air for every cubic foot of gas that is burned. So typically, it's 10 cubic foot of air goes into the burner. Theoretically, that's all the air. The burner needs for complete combustion, and then we have five cubic feet of air.

That's introduced around the heat exchanger and that's our secondary air and that's 50 percent more air than we need and that's a lot of times. I call that 50 percent excess air now, depending on how carefully we control the draft on an appliance. We can get that excess air down and if we get it down to zero percent. Theoretically, that would be stoichiometric combustion or perfect combustion.

But we don't do that because we always want to give a furnace excess air for safety reasons, because we want to make sure that all the carbon is converted over to carbon dioxide. So we always supply the burner with some excess air because we don't get perfect. Mixing of the gas and fuel goes through the combustion process, so the excess air is provided to make sure that it's consumed now, because this draft hood is there all the time, guess what the draft hood is always doing. It's always inserting additional air into the flue into the flue right and where's that air come from.

Typically, when you're talking about a draft hood, where does it get its air from inside the space around the furnace yeah inside the furnace around the basement? You know, typically in northern climates, were in a conditioned. Space is where the furnace is at in a basement and other climates where it's outside. It's not as big of a deal, but, let's think about what happens there for just a minute, because now a gas furnace requires an additional 15 cubic feet of air per cubic foot of gas burned to go up that draft hood every hour. So if we're talking a hundred thousand BTU furnace right, a hundred thousand BTUs per hour, if you took about a thousand BTUs and a cubic foot of gas you're talking about a hundred cubic foot of gas right and if we multiply that times 15, that's about 1500 Cubic feet per hour of air required so that air is constantly going up the stack 24 hours seven days a week and what temperature is that air? Typically, you think conditioned space temperature in the air and conditioned space in the winter.

Let's say: 68 degrees, 68 70 degrees. Obviously, if we kept exhausting air all the time, what would happen eventually in her house may get under negative pressure? It gets under negative pressure. Now again older homes. We had a leaky windows, leaky doors door seals.

It wasn't a big deal. We just pulled in fresh air to burn all the time before that draft hood equipped appliance it just pulled in that fresh air and got all the air needed. But if we're heating air from 0 degrees outside up to 70 degrees right because we're bringing it in the house, we got to heat it up and then we're turn around exhausting it again. Well, it's just like having an open window in your house and you're.

Just constantly exhausting there, you just heat it out your home, and so the draft hood became a big source of energy loss in a home, but it did, I think, important things. One of them was to provide us with fresh air in the home because, as the draft hood exhausted air out, then we had a you'll supply of fresh air coming in and the home would breathe a little bit and you get some natural ventilation in the house. The problem with that is that natural ventilation creates drafts so they're, uncomfortable and also, if you go back to our psychometrics before to take zero Degree, air at 100 percent relative humidity and then heat it up to 70 degrees. What would the humidity do they mean? He would drop, yeah might drop the 1012 percent, maybe 15 percent.

I don't have a psychometric chart run on me. That's why it took me a second then I was like. Does he actually want me to calculate this? No, no! No! I just wanted to understand the relationship. Humidity is gon na, go down a ton right if you just visualize the psychometric chart in your head and you just go at the bottom.

It's really skinny and you just went straight across you. Go Wow that'd be down in a 30 % region, maybe lower, and that's as dry, say Sahara. Desert is in the summertime. So now we're bringing in all this air because again when the furnace is running, we're using 30 cubic feet of air when the furnaces and standby we're using 15 cubic feet of air right.

That 15 cubic feet is constantly being exhausted up the diverter. So the trick was first of all, we always wanted to carefully control the amount of draft. So on some appliances, you'll see a draft, not only a draft hood, but also a draft control, and the draft controls are typically, you see a like field. Company name field makes them field draft controls, and a draft control is just the way if you had a really really tall chimney to additionally control the draft, because the whole purpose of that draft hood is to separate the appliance from the draft so that the natural Flow of gases through the heat exchanger is what induces the secondary air flow into the burner.

And if we're to block off that draft hood and let the chimney suck on that and then it would pull all the heat up through the heat exchanger. And it would cause a stack causes, accelerated stack temperatures and other issues, so the older furnaces, that's one of the standby losses that we wanted to eliminate. So what I'm trying to walk you through here is a little bit on history of furnaces understand that we are not burning gas any more efficiently than we did in night. Thirty, in fact, in 1930 we knew everything we needed to know and probably knew more about burning gas than most guys know.

Today. What we did on modern furnaces was two things: one was we eliminated standby losses and two we better controlled the ignition. So we didn't have things like pilot lights and things like that and then three we figured out that with the correct materials we could actually make furnaces that got the latent heat or the moisture out of the flue gasses and we got additional latent heat for combustion. We hit the old gravity.

Furnace didn't have a blower later they retrofitted blowers on those to give it force convection, which helped to move the heat more efficiently through the house than gravity, and also it provided a means to filter the air, because the old furnaces didn't have filters. Air flowed through just was cooled air in hot air out no filtering mechanism in there, because these drafts were so small going through a furnace. We couldn't filter the air. We didn't have any kind of filtering medium.

They had a blower in then after they added the blower in there they decided well. The next thing to do is to eliminate the pilot and they went to things like spark, ignition or glow wire ignition, where we actually used a piece of. I think it was nichrome wire and they just drew a small current through it to light the pilot and then let the pilot, on-demand and you'll see all these. If you work on enough gas furnaces, older stuff, you'll see all these different controls and changes along the way, and it's just really cool to see it.

So now we get into the 19, I want to say 1970s, maybe early 80s, and we had the gas crisis. We really didn't have a crisis, it was all lies, I think at the time, because we still have guests today, whatever it was all the sudden, we became very aware of the amount of gas we were using and we decided that we need to make homes use Less fuel and back in that day, if I'd, have to look at the exact dates, but I mean they actually had public campaigns on her to turn your thermostat down to 60. You need to keep her home cool and people just weren't into that. They wanted comfort that was Jimmy Carter's famous speech, be a patriot put on a sweater, a number that yeah.

I always thought it was I'm Jimmy Carter and I like peanuts, but I guess Jimmy. If you're listening to this love, you buddy, I mean Jimmy still around somebody. Nice yeah he's a good guy, but he was a tree hugger at heart. We had all these new modern efficiency furnaces.

Well, let's think about what we did here, because now we introduced: what do we want to do? How are we gon na make furnaces more efficient? Well again, it's about eliminating the stand, buying losses, so the first thing we noticed is in fact, if you go back to the older 70s, these were like the 60 % furnaces didn't have a blower. Then we added the blower. We got the efficiency up around 70 %, 72 % efficient and we jumped from 70 to 80 % efficient and there's a couple little things that went in between there. One was by metal, flue dampers on these old 70 pluses.

So we used to have a bi-metal flue damper that sensed the heat in the flue and it would open or closed to allow the furnace to draft and believe it or not. Your furnace would spill in the basement for three to five minutes. Well, that bi-metal warmed up before it would open far enough up to start to draft properly, and that was totally acceptable and what they did later on. Was they added in a spill switch that connected to the draft diverter and if the spill switch would not trip until it hit? I want to say it hit 200 degrees or 150 degrees Fahrenheit, and so that took a little while for that spill switch to get that hot.

So your furnace would spill and spill and spill, and as long as the bi-metal opened up before the spill switch tripped, then everything was considered. Okay and your furnace and start to draft naturally, but a little bit of carbon dioxide, water, vapor and he'd entered your basement. Not carbon monoxide, carbon monoxide is a product of incomplete combustion. We had these furnaces that they did that and then we also had retrofit kits guys.

Remember probably the g60, with Johnson Controls. Do you 60 that you could go in there and you can convert a furnace over to spark ignition? Those were the first flame rectification systems, at least that I remember, and they had the G 60 and they had the flue damper and they had a lot of furnaces that were using this mix for a while and then in the 80s we came out with a Draught induced furnace, so, let's think about what happened there for just a minute, because now we got this furnace that went from sixty percent efficient to eighty percent efficient. Now again, this is not combustion efficiency. This is appliance.

Efficiency. You've got to look at standby losses because we're not burn the gas any better and I fact I think in a lot of cases, we ended up burning it worse because of the new Vernor designs. So we get into this more complex heat, exchanger designs, because they're, making furnace is more compact and they're now draft and induced and they're actually made out of sheet metal. Now, for the first time and the furnace, the flame went from a carbon luminous flame to a blue flame.

So now we've changed the method of heat transfer of radiation in carbon luminous to convection and we're now to eating up the hot gases of flue gas right. As they go through the furnace, and we had actually go back to some of those 70s, obviously we're skipping ahead a little bit here, because some of the 70s also they're still drafted, equipped and used steel heat exchangers and used convection to heat with. But it sort of skipped over those a little bit, but those were in there also a lot of long furnace history here, but we get into the 80 percenters and we've eliminated the standing pilot we've eliminated the draught diverter and we've eliminated the standby losses of draught And we've got this 80 % efficient furnace, so the draft inducer motor on a furnace is designed to replace the draft hood and the draft hood obviously was designed to disconnect the furnace from the draft right. But now we got this really complex heat, exchanger design and the heat exchangers say: they're going left and right and up and down, and they have all kinds of narrowing passages in them and all kinds of things are changing a neat exchanger and it's just because now We can right, I mean that's the reason why they've made all these changes is because when you have force draft, you can do that not because they had forced draft it's it's, because if you're going to change the method of heat transfer, we're gon na go from Radiation to convection you're gon na have to have enough surface area and enough time because he transfers a function of time, temperature difference in turbulence.

You got ta have enough time, temperature difference and turbulence to extract the heat out of that gas of the more surface area that we could expose the more heat transfer by convection. We were going to get and it wasn't because we could is because they had to because they wanted to get that all the usable he out of the flame. Typically, we will want to see a stack temperature of somewhere of 325 degrees to 500 degrees on the outlet and if it's much above 500, we're wasting energy, if it gets down below 325, then we're gon na have a chance of condensing in the flue, because we Also need enough heat energy to make it all the way from the furnace all the way out to the top of the chimney, without condensing in the flue and with our old 70 %. Well guess what they were doing there constantly drafting and by the constantly drafting.

Even if it did condense in the flue, it was gon na dry that out with fresh dry air from your house, constantly pulling air through the chimney and would keep the chimney from corroding and falling apart. The liners of the chimney were tile liners and everything got nice and hot and stayed hot as long as the chimney stayed hot. The chimney stayed in really good condition. So when we got into these 80 percenters and we all of a sudden slap, the draft inducer motor on there now the function that draft inducer motor was to assist in pulling air through the heat exchanger, because the heat exchanger.

Just if you lit a fire net heat exchanger would not. Naturally, there was too much restriction for the natural draft to pull through that heat exchanger. It's just way too restrictive. So the draft inducer motor now was designed to create a pressure at the heat exchanger outlet that was equivalent to that of a natural draft appliance and because we could engineer the draft now on that draft inducer, we could actually carefully control the amount of excess air That we introduced into the burner - and now we got a furnace that we're not introducing any excess air into the system, except for through the heat exchanger Inlet, where we no longer have a draft hood, where we are constantly supplying some fresh air up for the chimney.

So not only do we have to introduce enough air for combustion, but we also had excess air for dilution. So remember I told you that the old furnaces they might have a 20 percent excess air above the heat exchanger, the new ones, all the new 80 percenters. We want to have at least 50 percent excess air all right. The reason we require 50 percent excess air is not only for safe combustion, but also to provide therefore dilution, and if we don't provide air for dilution, what's going to happen as the flue gases are gon na condense into chimney, if they condense in a chimney, we're Gon na have a whole host of other issues in there very important to understand that now we have a couple of different things going on, because if the draft inducer motor doesn't start - and we have a call for heat and the gas starts firing in and there's No air coming in where the flames gon na try and go.

They jump back out at your face. They roll out jump back out at your face. We're gon na have a roll out on through that's, not a good thing, so we needed a roll out switch in there and how do we prove the draft inducer motor was actually running in modern systems. We use the pressure switch to do that and that's the same way we did in the old systems.

The pressure switch is used to create or sense the draft that's created by the draft inducer motor. So the first thing happens, the doucer motor starts creates a draft closes, a pressure switch that tells the furnace. The ignition cycle can continue right now. The other thing that we did with these new modern furnaces, because again we had no draft on there was we eliminated the pilot light and again you will find furnaces out there that are 80 percenters that have a pilot light, believe it or not, because even though The draft inducer motor shuts off there's still a little bit of draft through the fan wheel.

That's enough to exhaust out the pilot gas in there. We could go on for hours on how many furnaces that were extra designed at all the in-between stuff that happened. It was a progression through our industry and and also it's driven by marketing, guys like oh, I hate hot servers, igniters and Rhema go oh we're coming out with a furnace with a pilot light and guys are like. Oh, I understand pilots, I'm going back and selling all these furnaces with pilots and that's what guys would do.

Then. I hate spark ignition because I don't understand it. Well, we have a new hot surface igniter, it just closed. Like a light ball, you understand it.

My faulty I understand a light ball. Okay, well, we've eliminated the spark which is so confusing and we're gon na go to a light bulb day ignite your gas right. So all of these are also their marketing decisions along the way. Also, and that's just away our industry was nobody likes change in the industry.

We get this 80 % efficient furnace and obviously it's got a blower just like the 60s and 70s that, as they grew up through their will, eliminate the giraffe to it eliminated the pilot. We got out now a high surface ignition and furnaces. We consider them all 80 percenters. Now question always ask people is why don't we see 82 % 83 % 85 percent 7 percent 88 percent efficient furnace? Why is it that we go from 80 to 90 percent? Any idea on that Brian, I think I know the answer to this one, actually, because as soon as you go above 80 percent now you're bumping into the point where the exhaust is gon na start condensing, moisture and as soon as that starts happening.

What you might as well go up and extract all the heat, all the latent energy out of it, as opposed to only doing it partially you're a hundred percent correct again, the point is: is that the reason? Why is because, if you're going to get into the condensing range of combustion, then you might as well take it all the way and get all the latent heat out of it? That you can, because otherwise you have to build a furnace differently. If you're going to be condensing the combustion byproducts, that's sort of right, I would actually say it's, because if we get the stack temperature, any lower, we're going to condense. And if we condense on a non condensing appliance, it's going to lead to a host of huge problems. Induced draught motors rotting out heat exchangers rotting out furnace chimneys, falling apart, leeching white stuff on the outside of the chimney, as it eats out the mortar all kinds of things that literally destroy the non-condensing appliance, because that non-condensing appliance doesn't have a heat exchanger.

That's designed to be corrosive resistant, in other words, it's not made out of stainless steel, and so it is going to literally fall apart and when you see 80 percent efficient furnaces that are full of rust. That are all these other issues. There's two things you need to look for: one is obviously chemicals and again we'll talk about that in a later podcast. No chlorine, bleach, dryer sheets things like that bad bad, bad around furnaces.

You don't want to have those around furnaces, but the other thing is: you have a condensing taking place because the furnace is not set up properly or it doesn't have enough draft or for whatever reason, there's something else going on there. You got to look at these 80 percent furnaces. Obviously they have a primary heat exchanger. They have no secondary heat exchanger, they have a lot of times serpentine designs and, as the designs get more more complex, the heat exchangers get smaller and smaller and smaller than ends.

Today the furnaces are three foot tall right because they have very likes heat exchanger designs that allow them to extract all the heat out of the flue gas in a very small amount of area and basically, 3d modeling CAD. All those kind of things allowed us to make these more complex heat, exchanger designs, or they used to have a clam shell, which was just two pieces of metal that were stamped and then welded or riveted together, but all those heat exchangers on those older 80s. That's just the way that they were engineered. There are non condensing appliances and now the appliance because it gets its excess air for combustion through the burner and through the secondary.

The input on those things becomes critically important. Another thing I want to talk about in later podcast, but is commissioning a gas furnace, because there's only a couple things that we can do and we don't do them right. It's going to cause just all kinds of nightmares with furnace operation. So then, the next thing that happened is we got to the 80 and 80 % of furnaces were only around for a short time before they actually came up with a 90 %, I think, probably the first rule 90 %.

I remember was the Lennox pulse. I'm sure there was other ones out there, but Lennox decided everybody wanted a moped in their basement and it came out with a pulse furnace and it was probably one of the best 90 Plus furnaces ever manufactured because it all the way it worked pulse combustion is Extremely efficient and it was basically an explosion, and every time I exploded in the heat, exchanger they've created a vacuum that would pulling the next mixture of gas and air and it would explode again and next picture. Gastner explode again and after lit the previous explosion lit the next one, so there's still some gas or like glow plugs in your diesel right once your diesel engines running, you don't need to run the glow plugs anymore. They'll just keep running with you know from the hot food gases light in the next charge coming in, but the 90 Plus.

If we eliminate the pulse furnace for a minute and we go back to condensing furnaces, really the only difference between an 80 plus and a 90 plus, the big big differences are we've added in a secondary heat exchanger and the function of the secondary heat exchanger is To pull additional heat out of the flue gas and basically condense the latent energy out of the flue gas, but it pulls the heat and the humidity out of the flue gas to get this additional efficiency. Now a couple of interesting things here: you'll see that we go from like 90, 91, 92, 93, 95 or 95 96 97 %. I don't know if I've seen any above 97 % combustion efficiency or 97 percent efficiency, but I think 97 percent about where they top out at and when we look at these furnaces, you know well, how do we get from 90 to 97 percent? Well, we actually did it by not just lowering the flue gas temperature, but also extracting the latent heat of combustion, the latent heat energy out of the flue gas, which is the moisture just like when you start your car and it's running, you see moisture dripping out Of your tailpipe well where's that moisture come from well, it's a byproduct of combustion. It's any time that we're burning fuel, a byproduct, the fuel is water and that water, if we turn the water vapor into liquid water, we get about 970 BTUs a pound of energy.

Out of that, that's condensed so the original 90-plus furnaces realistically, all they did was cool the flue gases down and in fact there is very little condensing that took place if any. If you go to an old, 90-plus furnace and you actually pull the condensate drain off and you watch it run, you might get a dripper a condensate out of it as it's running and it was still called the condensing furnace because it ran at the threshold of Condensing but they really didn't condense, much of the heat energy out. Now you get into a 97 % efficient furnace and it'll run 1/8 to 1/4 inch stream out of that same trap, because now we're extracting additional heat energy out of the flue gas and we're getting into condensing range deeper into the condensing range we're getting the flue Gases cooler, but the other thing that we're more carefully doing is controlling the excess air. Remember we said excess air is necessary for safe combustion, but excess air is also what kind of error.

What was it used for non any eighty plus, it was dilute dilution which train doesn't care? Okay, that's the word. We brought our dilution air in along with the combustion air. So now the dilution error is going all the way through the heat exchanger on the 80 and a 90 % efficient furnace. What happens if we add in dry air into the combustion process and we had additional dilution air in? What do you think's gon na happen? To her condensing on our condensing furnace, it's not gon na condense! If you're, adding in dry air, not gon na get that's we're trying to flue gases out right.

So this becomes like super important if you're going to get this 97 % efficiency out of this furnace, that you have the input correct again. Well, we get into more detail on setting up furnaces I'll go through this, but it is absolutely critical that you have the excess air trimmed to the correct amount. And you have the input correct on that furnace, because, if you don't have it set up properly, the dilution air is going to dilute the flue gasses and you're not going to condense you're not going to get that efficiency out of your furnace. So gosh.

It's got to be ten years ago now I actually went to CSA labs, which is the old Aga in laboratories in Cleveland Ohio. The first thing they do when they test a furnace, is they take it out of the box and they pull the offices out of it and they put new or faces in it. Then they the meter and to make sure the inputs a hundred percent correct. So not a single furnace is ever tested, as it was delivered from the manufacturer, because CSA doesn't really care what orphis is coming at, what they care is.

What is it rated? So they look at it's a hundred thousand BTU input. I'm gon na put a hundred thousand BTUs a gas to it right. They have a cutlery meter there that measures the exact amount of heat energy that's produced by the gas. They know exactly what size service they need.

They get the input spot on the furnace. Then they test it as it's published to make sure it meets in safety and efficiency requirements and doing it the way CSA labs. Does it every single time the furnace will produce the same results as it was tested at the laboratory was manufactured at a carrier. Trane Lennox, whoever, but because a lot of times in the field don't go through and set up the furnace properly it never realizes its efficiency.

That's one thing that we'll cover in another podcast, but anything it's just very interesting. When you understand, we start looking at how this industry works and how the efficiency works. Just because you pull it on the box - and it says this 97 % AFUE on the label doesn't mean it's 90 % up a if you eat, as you set it up and so just important to understand. So now, we've added in the secondary heat exchanger.

We dropped the stack temperature down to below 120 degrees. The only thing coming out of the flue gas now is carbon dioxide, water, vapor and heat energy, and we got that heat energy down to a minimum, we're condensing as much of the moisture in the secondary heat exchanger as we can. We can condense a hundred percent, but we have some of the exhaust gas coming out. The side of your house is a little cloud like just like it's a dryer vent and we've now changed the draft inducer motor from a metal one to a plastic one because a lower temperatures but be corrosion resistance, because flue gases also contained acids primarily because of Chemicals in your home, if you have a sealed combustion, where it's pulling air from outside, which I would highly recommend you never ever install a condensing furnace without the inlet pipe on, because it'll tear up that furnace it'll cut years and years and years off of it.