Derek Cole explains why HVAC units short-cycle: an oversized unit reaches temperature too fast, causing repeated on-off cycles that use three times more power than steady operation. He walks through diagnostics: check the unit, insulation, ducts, and load calculations to ensure proper sizing.
On this episode, we talk about should I shade my unit and my unit turns on and off all the time. What is the problem? You ask your comfort and energy questions and they get answered. This is the Ask Derrick Cole Show. Hey, this is Derrick Cole. Welcome to episode 69 of the Ask Derrick Cole Show, answering your home and energy questions. It's been a nice week, very busy week. That's why we're doing this on Thursday. Yeah, today's Thursday. So yeah, in Atlanta for a few days and flights and 24 hours and I'm back. So let's get into the show. Should I cover up my unit in the winter? If you have a unit like an AC outside that you're not using in the winter, then I would recommend covering up. That way you keep the leaves during the fall and the winter. You keep the leaves, you keep the ice, you keep all the stuff out of it. Now, the challenge in this area is most people have a heat pump, so that's not really possible to cover the unit up because it needs to operate obviously in the heating season. The unit operates in the AC and the heating, so that is a challenge. They do make a product called a— I think it's called a Cool Cap. Actually goes on top of the unit. They can go over it when the fan's off, and when the fan's on, it'll pop back up and lower itself when it's off again. That will help quite a bit, especially if you're in like a wooded tree kind of area for the outdoor unit. I mean, my unit outside is by itself in the sunshine with no trees around it, so I'm good to go. I don't need to cover it up. If I had an AC unit I still want to cover it up because there's nothing going to get into it. But some people do live in that environment, would have a lot of pine trees, a lot of pine straw, and a lot of leaves. So in that situation, if you have an AC, I would cover it up. If you have a heat pump, you can't put a cover on it unless you go with a cool cap, which will go up and down depending on if it's on or off. So be careful about that. One thing that's One thing I've also seen that is a problem, some people will actually, and you've seen it if you've looked on the side of houses, some people actually put like a roof on top of their unit, which is like 2, 3 feet away from the unit. That's too close. The unit needs, I think the minimum is 5 feet. Above it for the fan to operate. That way the fan can— the top of the fan is blowing the air up. So if you have something constricting that and pushing the air back down, obviously you're going to have a fan problem later on. So if you're going to put that roof over the unit, make sure it is high enough to whatever the unit is. Check the specs on it. It'll tell you the clearance as to how far it needs to be from the house. How high it can go before something gets in the way. So make sure all those are taken care of because, uh, I went to a house one time and, uh, it was Fayetteville and the deck was like here, the unit was like here, and she was like, I've been having some fan motor problems. I was like, yeah, no kidding. Let me tell you why. So basically our unit was sitting there and once you got the deck built on, they built over the unit, so you had to go under the deck to get to the unit. Obviously, we moved that unit when we replaced it, so be careful with that and make sure you're following the specs and not causing more damage than what you're trying to prevent. Was that right? More damage than— Causing more— Preventing damage. I say it wrong? I think I said it right. Causing— next. My unit will turn on and off repeatedly. What could be causing this? When your unit is turning on and off repeatedly, it's— you could have a problem in the unit itself. What I've seen also is the unit is too big for the house. I was in a conversation with somebody the other day and they said, "Well, you know, I got a 3-ton unit. How about I just go to like a 5-ton? Won't that cool the house faster?" Yes, it will cool the house faster, but your challenge is now you're not dehumidifying because it's coming on, cooling the house down, turn it right back off, on, off, on, off. The most power that unit pulls is when it first starts up. So I think Advanced Energy, when we did back with them in Raleigh a few years ago, did a study and if a unit ran for 8 hours constantly, pulled less power than if it was started and stopped, I think it was 3 times. So starting and stopping is not good for the power of that unit. It's also not good for the unit. It's kind of like I've talked about before, miles per gallon with your car. Obviously it's more efficient for you to hop on the interstate and drive 8 hours than to spend 8 hours in stop-and-go traffic, right? You get better gas mileage out of the long trip. Your unit's the same way. So if it is cutting on and off, chances are the unit is too big for the home and it's satisfying that thermostat very quickly and turn it right back off. It's getting cold or warm again and then it's coming back on, satisfying. Coming right back off. So the challenge with that would be wear and tear on the unit as well as running up your electric bill because it's wasting energy. And when you get into the summertime, you're not dehumidifying the house properly. So you walk into some of these houses and yeah, 75 degrees, but it feels kind of clammy and sticky. That's because it's not dehumidifying properly. So when it's, you know, 30 degrees outside or 90 degrees outside, for that unit to run all day is not uncommon. Okay, it's not going to hurt anything. It's better for it to run longer than start and stop, start and stop, start and stop. Now I would have it checked out just to make sure you're not having some, some kind of problem in the unit itself. But if the unit is okay, Then you have to look at where it's at, the home and the duct system as well. We tell our guys all the time, there's 3 aspects to a home. There's the unit itself, there's the envelope, which is the home. Is something causing this to happen? Did I change something? Did I change a window? Did I leave something open? Are we missing insulation? Is something causing this to happen?, and then you got your duct system under the house as well. So check all those things to make sure it's operating correctly. And if all those check out, then we have— we need to do a load on that house to make sure that unit is sized for that house properly. And if it's too large, then we can fix it. All right, that's it. Episode 69 of Ask Derrick Cole. Make sure you hashtag your questions, #AskDerrickCole, Facebook, Twitter, and Instagram. And we'll get them on the show.
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