Derek Cole explains why longer AC cycles beat short bursts, compares it to highway versus stop-and-go driving, and recommends keeping your thermostat fan on AUTO in humid climates to prevent moisture problems. Large temperature setbacks on hot days make your system work harder during peak demand.
Questions this video answers
Longer run times are more efficient if the system is properly sized; short bursts indicate an oversized unit, while a too‑small unit will run continuously.
Keep interior doors open when possible to allow conditioned air to return to the system; if doors must be closed, ensure there is an undercut gap so air can still flow.
Energy Star recommends setting back the thermostat while away, but Derek prefers a constant 75 °F (with a cooler night setting) because large setbacks on very hot days can cause the system to work harder during peak demand.
In humid southeastern North Carolina, the fan should be set to AUTO to avoid moisture problems; running the fan continuously can introduce humid outdoor air and may cause blower‑wheel imbalance if dirty.
Chapters
Hey, on this episode, which settings are most efficient for my air conditioner? Should I close the doors in my house? And should I leave my fan on? 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 35 of the Ask Derek Cole Show. Very big personal news for me, um, my stomach's kind of hurting. Uh, I thought I'd share that with you guys. Uh, so, but that's fine, we're just going to keep rolling. So if you missed episode 33 and 34, uh, what's going on? What's wrong with you? Go back and watch them because they're there getting great reviews. 34 maybe? 34 did. Yeah, 33 was good. Before then it was terrible. I mean, it was, it was not even— you don't even, you don't want to see it. So, uh, just kidding. All right, let's get into the program. What is the first question?
Is it more energy efficient for the air conditioner to come on for short bursts of cooling or to come on and stay on for long periods?
Yeah, great question. So you got to think about it kind of like miles per gallon. So think of your air conditioner as your car. Is it more efficient when you drive for you to be in traffic, stop and go, or is it more efficient for you to be on the interstate and you're going? Which one's better? The interstate, right? So if the system is sized properly and is designed properly, It will run for longer periods than if it was too big of a unit, it would turn off quickly. If it was too small of a unit, it would run all the time. I had a customer come in here a couple years ago and she said, "My AC won't stop running. It's like 95 degrees outside." I said, "Well, what's your set point inside?" She said, "Like 75." "What's the temperature?" "75." I said, well, that's good, right? She said, no, it won't stop running. I said, well, it didn't want to get behind the temperature. So kind of when you think about it, so when you drove up here from your house, how many times did you turn the air off in your car? She said, I didn't. I said, why not? She said, because it would have got hot. I said, exactly, same way in your home. So on those really hot days, it's going to run and run and run because it doesn't want to get behind. So if you got it set on 75 and it gets to 75.2, it's going to turn on. Now they don't show you the point and the dots between the numbers because that kind of freaks you out, because it'd be like 75.6, you're like looking all the time like 75.6, oh my goodness, it's getting hot. So they, they only go with the round number, 75, 76. So the system should be size properly and if it's working properly, it is going to run. You want longer run times because it would be more efficient to run longer. So hope that makes sense. I think that answered the question. The answer pretty good?
Yes, very good.
Awesome.
Should I leave interior doors open or closed during heating and cooling?
You go into some houses and the door's shut and you open the door and it's like 65 degrees in that room, you're like, oh, feels good. So it depends on the house. Now, the ideal situation would be to have all the doors open all the time. Some houses, when you shut the door, it is right to the carpet, so it is trapping the air in there and it's not coming back to the unit, which is a problem. Some houses or mobile homes really have that undercut door where they got, you know, 2 or 3 inches there where you can shut the door and the air is just going to keep flowing out of that room. So that's good too. Now again, the ideal situation, keep them all open because whatever goes out needs to come back. So you don't want to restrict that airflow coming back in any kind of way possible. So if the air is blowing out, you want it to get back to the return. Again, air is like water. Whatever is easier is the way it's going to go. So if it's hard for it to come back to the unit because your door is shut, it's going to pull air from the crawl space, from the attic. It's going to get the air back to the unit. So you want to make it conditioned, filtered, clean air coming back to it versus the air from outside, which you can't control. Keep the doors open when possible and watch for the door undercut because some folks, I've been to the house and the door and the carpet is so thick when you shut the door you can either pull it and it's really tight, the air is not coming back very easily. And then some houses you shut the door and they got like 4 inches under and you're like, oh my goodness, that's plenty of room. So leave it open when possible. If you need to shut it, just be conscious of what needs to happen. In my personal house, I have to leave my door cracked a little bit because my carpet kind of comes right up to it. So if I want to shut my door, I kind of shut it with a gap in it. That way the air gets back to it because the unit really freaks out when it has no airflow.
Is it better to set the thermostat to high temperatures while at work all day and cool the house when you get home to a comfortable comfortable temperature, or to keep the thermostat just a degree or two higher during the day so that the cooling unit doesn't have to work as hard during peak hours to cool the house?
Okay, so you're going to get two answers to this question. You're going to get my opinion, and then you're going to get what Energy Star tells you to do. Energy Star will say yes, set the thermostat back while you're gone, and then when you come home You'll save energy by doing it this way. I don't personally do that, especially on a 195-degree day. If you set that thermostat back, it's going to have a harder time to come up to temperature when you get home at 5:30, 6:00, because it's the hardest— hottest part of the day. So now you run that top speed with everybody else on the hottest part of the day. So I wouldn't go with that method. I like keeping my home at a constant temperature unless I'm on vacation. So I keep my house at 75 all the time. I don't really vary from that. Well, let me go back. I do keep it a little cooler at nighttime. When it's time for bed, I yank it down just a little bit more because I like it being cool. But personally, I'm not a fan of the myth of setting thermostat higher, then when you come home you don't have that challenge of catching up and that's a hot day and it's not going to do it. I don't see where you're saving that much energy doing it that way. Again, that's just me. Energy Star, the energy department will tell you yes, that is the right way to do it and you need to do that to save energy. It's just a difference of opinion.
Does setting the fan switch on my thermostat to the on position cause air imbalances in my home?
Uh, no. No, it doesn't. Um, in our part of the country, southeastern North Carolina, you really shouldn't do that, like, ever. You want to always have the fan on auto, otherwise you're going to cause a humidity moisture problem in your house. So we always recommend it be on auto. When we have installed the new system, I know I've been to two personally myself where the homeowners were putting it on, on, on for the fan and black stuff was coming out of the grill and they're like, what's going on? And we get there and the fan is on, on. Okay, we'll put the fan on auto. The challenge is that, yeah, even though it's 70 degrees here, humidity is like 80%, so you're just bringing that moist air into the space, and you want to dehumidify and get that out. So you want to leave it on on. Now up north, they have their fans on. I think even like Illinois and They might leave it on all the time, and it's funny because it's dry. It's a dry climate. That's not us here in North Carolina. So leave it on auto. I've never heard of it causing an imbalance of air problem. Not sure what's going on there. What can happen with that fan is the blower wheel will become unbalanced, and that might be causing some of your issues there. Um, so, okay, let's check it out. Um, dirt, debris, and everything can get on that little blower wheel, and it will have trouble pushing the air into the space. So make sure that it's clean, and it will be balanced if it's clean. If it's not balanced, then fix it so it's balanced. That's it. All right, that's it. Episode 3-5 in the books. I feel pretty good about it. How about y'all? Yeah, feel good about it. Hey, I need your questions, so hashtag #AskDerekCole, Facebook, Twitter, Instagram, however you want to do it. Ask me your energy home questions and we'll get them on the show. But until next time, I guess we'll, we'll say bye. Okay, I'll see you later.
