Hey this is a short episode of the HVAC school podcast, I'm Brian, and this is the podcast that helps you remember some things that you might have forgotten along the way as well as helps you remember some things you forgot to know the first place and today We're talking about well that systems under sized and that's something that I hear too often and we're gon na talk about why I'm sick of hearing that and what you can do about it. But before we get into that, I want to thank our sponsors nav AK. They make all kinds of great tools, a lot of them that we use at Kalos. I've especially been enjoying the battery-powered flaring tool from nav hack.

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So here we go, we're talking about the system is under sized or the technician who says it's under sized right. That's the answer that technicians give sometimes when they show up to a house and they look at the tonnage and it doesn't seem like it matches their idea of what proper sizing should be and unfortunately, for a lot of technicians. That's 500 square foot per ton. So you go to a 2,000 square foot house, it's got a three ton unit and they say well by golly ma'am.

The reason why your unit isn't cooling properly is because it's under sized. It drives me crazy, but there are more circumstances where this whole you're under sized comes up and more than just circumstances where a technician who misunderstands load calculation. So let's first just mention quickly. This kind of dovetails on last week's podcast, we're talking about you and our factors the way that we do a load calculation on a home.

The way we know how much heat to remove or add to a home, and specifically we're talking about removing heat here in the case of cooling, but it works just as easily. The other way is that we have to factor in how much heat is entering or leaving the building, so temperature difference between the desired inside temperature and the outside temperature becomes a really big factor when we talk about heat escaping or entering the space. So that's something we have to think about. We have to think about installation, but then we also have to think about gains.

Heat gains on the inside of the space. Now heat gains happen quite often, so you have the people living in a space when you're trying to cool the space. You have electronics, so on and so forth, but you very rarely have heat losses on the inside of the space. In fact, I can hardly think of a circumstance where you would have heat losses on the inside.

Maybe when little Timmy likes to play with dry ice and it's laboratory, I don't know, that's the only way. I can think you actually losing heat in the inside of a space. This would come up and maybe a high-rise in a big city where you have all this class, and so you have heat coming in from the Sun, and then you have heat being generated on the inside and it may be very cold outside. But by the time you figure out the internal gains and the radiant gains you may not need heat.

You actually may need cooling and that's where a lot of times you can use the free cooling from the outside via an economizer, to help compensate for that. But in residential applications we see he lowed from the inside. We see heat load from the outside in cooling mode and then we see losses to the outside in the heating mode and so there's a lot of different factors to take into account. But it's all about heat gains and heat losses.

It has nothing to do with a square feet of the space or even the cubic feet of the space. For that matter there are some approximations, some rules of thumb that may be used in certain geographies. Obviously it varies from location to location, but those are certainly not absolute and they're very unscientific, and so when the technician goes to a regular residential house, we'll just give an example here and that's a 2,000 square foot house and they see a three-ton unit, sometimes they're Gon na say well, I've been in a lot of these houses, and three-ton is just too small, and that may be the case. This is what I want to point out that it may be the case that three tons of cooling is not enough to cool that 2,000 square foot house, or it may be the case that it is, but sometimes you're gon na go to a house as a Technician and it's having a hard time, keeping up and either the summer or winter.

So it's not heating enough in the winter or it's not cooling enough in the summer, and so the technician diagnoses that by golly you need a larger unit or in some cases the customer will have already self diagnosed that they talked to their neighbor and they got The professional or unprofessional opinion from somebody who's, not in the trade that their unit is under sized, maybe a Salesman doesn't maybe a Salesman goes out. They talk to the customer. The customer is unhappy with how their old system has been performing. I've lived in this house for 10 years and I've never been happy with how it cooled the house.

I want to keep it 72 degrees, even when it's 98 outside that sort of thing, and so that salesperson wants to put a bigger unit in here's. My encouragement, if you can help it don't put a bigger unit in I've, talked about this in previous podcast. But it's just bears saying again: if you can help it don't put a bigger unit in and a lot of times you can help it because sometimes the equipment's just not working right. So it's just as simple as getting the equipment working properly.

That's the most simple! A systems not under charge - or maybe it has a dirty filter or some other air flow problem, dirty blower wheel, dirty of a per to call something like that and that's what was causing it not to cool properly, and so that's fairly obvious for a technician. But you'd be surprised how many texts don't go through everything, and so let's talk about some other things that you got to go through before you tell the customer that is under sized and by the way, I don't think you should generally do that anyway, because there's Always options of how to solve problems that doesn't involve oversizing equipment or increasing the size of equipment. So the first thing would be: let's look at the sensible and latent load on a space. So, first off, let's say you do a load calculation and you find out that it is too small.

Well, let's look at. Is it too small on the sensible side, meaning temperature, regular conductive heat gains, or is it to some on the Layton side? Is it that you have more moisture than you need and it's really important to figure out when you're sizing equipment isn't the Layton? That's the issue, the moisture load, or is it the sensible side so because sometimes you can fix that just by making some air flow adjustments system air flow adjustments. If you increase air flow on a system, you will generally increase the sensible heat. I mean that's up to a point: there comes a point where it becomes diminishing returns and you really can't get 100 % of your total rated capacity with just sensible, but sometimes speeding up the blower, especially if you're in a drier climate - or you don't have a Lot in the way of Layton loads, you can speed up the blower, get a little more capacity out of it and that's an option in some cases, if the issue is Layton, sometimes you can slow down the blower and remove a little more moisture.

So that's one thing is: let's look at is this problem that the customer is experiencing related to moisture? The relative humidity is too high that are uncomfortable because of that, or is it sensible? Because if the issue is relative humidity, you do not want to oversize that equipment. You do not want to increase the size, because when you increase that capacity, you are generally in most circumstances going to increase the relative humidity because you're going to decrease the runtime. So that's something to think about. The next thing is: let's look at leakage.

Leakage is enormous leakage, both in the ducts as well as leakage that we call infiltration, which is air, that's coming in from outside or other unconditioned spaces into the space. So I'll give you a quick story. I was working in a house where the customer has little previous five years. That said that it just wasn't keeping up just wasn't cooling properly, and we had actually been there a couple times as well.

My company and finally I just I went up in the attic and I didn't see anything at first, but I crawled way back and I actually found that where the returned came in to the main box, it was actually almost completely disconnected in the attic. So it had been running for who knows how long drawing in attic air now we should have saw that we should have saw it on the return side. But for whatever reason we didn't catch, that it was maybe five six degrees difference and we didn't pick that up and when we measured our return temperature. So it's something that could have been caught without even having to do that.

Visual inspection. But, of course that solved the problem once we got that repaired, so looking at duct leakage is huge. Looking at infiltration is huge: do you have giant holes to the outside or into the attic or into the floor space where you have communication from the inside air? With the outside air, do you have a lot of? Can lights? Can lights are notorious for allowing our infiltration through them? So that's something to look for. Is there on the infiltration side, also doors and windows? Are there big gaps and cracks around your doors and windows or the door sweeps in place? All of these things can have a big impact both on your sensible and your latent loads.

When you have a house, that's not keeping up. Those are the things I want to look at next to be insulation. Insulation is enormous again. Another similar circumstance actually was working at a professional golfers house in Windermere, and they had been living in the house a couple years and they said this unit is clearly under sized.

It's not keeping up. I popped my head up in the attic and one section is a big house, so there's different sections of the attic, but this one section of the attic that clearly nobody had checked and there was no insulation in the attic whatsoever. They just never insulated. So insulation is a huge factor.

Attic ventilation is a huge factor if you have an unconditioned attic space and it isn't properly ventilated, where you don't have high low ventilation like you're supposed to that, can result in a higher attic temperature, which means that you have more gains from the attic into the Space, so these are all things that factor in to does the system keep up even things like shading and the windows? Are you closing the drapes or you're closing the blinds? Is there tinting on the windows? Is there a tree shading that side or or not? Obviously, the direction that the house faces is gon na make a big difference. Those southeastern and southwestern exposures are gon na get hit at different times of the day, so the south is kind of the direction, at least in our part of the world, where the Sun sort of swings. So the South tends to get it a combo of some sunlight most of the day, but then obviously the Sun rises in the east and sets in the west. So in the morning that southeast corners gon na get a lot of heat and the evening it's gon na be the southwest corner.

Well, if you have a master bedroom, that's sitting right in the southwest corner with a bunch of open glass. Well then, you're gon na have a lot of radiant gains in that room right before the occupants go to sleep, and that's gon na tend to be a problem there. So you could have a big improvement on your cooling if they put an awning on that side or some other method of shading heck you've, even if they put a tree up the outside that side of the wall that can really help, or maybe some window tinting. So maybe some new drapes there's a lot of different things that can be done and if you can think in this way, then the solution doesn't always have to be increasing the size of the air conditioner.

Now why do I not want you to increase the size of the air conditioner? Well, there's a lot of reasons, but the most is that replacing an air conditioner with a larger one is rarely that simple. It's really just as simple as pulling out the condenser pulling out the air handlers slapping in a half ton large or a ton larger. Does you have all the old duct work, which is very possibly undersized in the first place, and now you're gon na try to push more air through it? You have your copper line, sizing, you have your wire sizing and then you have the physical dimensions of where you're gon na fit this air handler furnace, which can also be a important consideration so especially for salespeople or if your sales technician. If you do sales and your attack as well, you really really really try not to put in larger equipment.

That's gon na be my suggestion. Even if the equipment is under sized, I would look at the customer and propose to them maybe some options of reducing loads. In some way, whether it's insulation - whether maybe you do insulation - maybe you can do a little bit of sealing. This is a small change, but you can do things like changing lighting from incandescent or halogen to LEDs, or a compact fluorescent.

The kitchen and bathroom ventilation is huge from a latent load standpoint, so putting in higher performance bath fans that maybe have humidity sensing or occupancy sensing in them them it's an option even instructing the customer on how to use a kitchen range where you're not going to Use that exhaust hood unless you're cooking, obviously you don't want to run it too long, but then also you want to run it anytime. You are cooking, maybe putting it on a timer switch would be an option so that way it will automatically run for only a certain period of time and not run too long. There's a lot of things like this that you can do because, obviously, if you have somebody taking a shower or cooking, you want to fan out that moisture. But then you don't want it running longer than that, because then you're gon na be infiltrating more from the outside.

Whenever you have those big fans running, it's a lot of things like this. This is all kind of building science stuff. This is the stuff that bill Spohn talks, a lot about on the building, HVAC science, podcast or Kristof the positive energy sense to talk about on his building science podcast. This isn't all HVAC stuff, but it is very practical for a technician, because here's what I don't want you to do once again, I don't want you up sizing equipment now as an absolute worst case scenario, if you have a space that is just under sized and It needs a bigger piece of equipment.

Well then, what I'm gon na suggest doing is find a section of the house: that's mission-critical, like a master bedroom or an office or a game room, or something like that and branch that off and install another system. On that say that way, it gives you some zoning control. It's also a good opportunity to maybe talk to them about ductless, because in a lot of cases, a single zone ductless system may be more practical from a cost standpoint, and now that they make a lot of brands carrier mitsubishi, we deal they both make. Really, nice sealing cassettes, recess, sealing cassettes, sometimes that's an option if they don't want to have the wall mounted type of design.

So a lot of things like that that I would suggest that you consider, rather than taking the old box, that's maybe it's a three-ton and making it to a four ton or a three and a half. I I just don't suggest doing that unless you have exhausted every other possibility and it's the only way to go, even if that equipment is at the end of its life up sizing equipment causes more trouble generally than it solves, and I'm just here to encourage you To not just think in terms of it being undersized think about you loads, think about how the equipment's working think about infiltration from the outside and look for ways to reduce heat, both latent and sensible, rather than just throwing more air-conditioning at it. Alright, thanks for listening, we'll talk to you next time on the HVAC school podcast.