In this episode of the Ask Derek Cole Show, Derek explains why a larger HVAC unit is not automatically better for a home. He walks through the importance of proper load calculations, showing that an oversized unit (e.g., a 5‑ton unit for a house that only needs 3 tons) will short‑cycle, fail to dehumidify, and waste energy. He likens the effect to a car stuck in stop‑and‑go traffic versus cruising on a highway. He also stresses that the unit’s capacity must match the existing ductwork; a 20‑ton unit cannot deliver more than the duct’s 3‑ton airflow. For a problematic “Carolina room” (sunroom) with three glass walls and inadequate ceiling‑fan cooling, Derek recommends either installing a dedicated mini‑split system or redesigning the ductwork for zoning with a room‑specific thermostat/sensor. He illustrates how exposure (south‑west) drives heating loads and why a single thermostat in a hallway cannot adequately control such a space. The episode ends with a call for listeners to submit questions via #AskDerrickCole.
Questions this video answers
No. An oversized unit will short‑cycle, fail to dehumidify properly, and waste energy, even though it may cool the space quickly.
Install a dedicated mini‑split system for that room or redesign the ductwork to create a zoning system with a room‑specific thermostat/sensor. Mini‑splits are often the most practical solution when zoning is not feasible.
Chapters
Hey, on this episode we talk about bigger is not really better for your home and my Carolina room is not being cooled by my ceiling fan. 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 65 of the Ask Derrick Cole Show, answering your home and energy questions. Hope you're enjoying the cold weather. I know I am. So with that, we'll get into the questions we get most often.
Does a bigger unit mean I am getting a better unit?
A bigger unit is not necessarily better for your home. If the unit is too large— so we go to your house, we do a load calculation on the house. Okay, say this house needs a 3-ton unit. Needs a 4-ton unit, 5-ton, whatever. So if you need a 3-ton unit, it does you no good to put in a 5-ton unit. And the reason is because you start having a problem dehumidifying that space, especially in the summertime. This time— well, in the summer, that time of year where you have humidity problems, you have trouble dehumidifying the home because it's not staying on long enough to— it's cooling the house down, but it's not dehumidifying the house. If that makes sense, it's kind of start and stop, start, stop. Comes on, gets it to 75, turns back off. The problem with that is you're not dehumidifying, you're not getting the moisture out of the air. So even though it's a 75-degree home, the humidity is so high it feels cold, clammy. You might have felt that in some houses before. It feels kind of— feels cool, but it feels kind of weird. Is because the unit's too big for that space. So if it's not dehumidifying, I'll put it like this. All right, so let's relate to a car. So you go on a car ride and it's 95 degrees outside. So when you first get into the car, you're blasting the AC, right? As you start driving for like 30 minutes, an hour, you turn the AC down, and then eventually you actually turn it up a little bit because it's too too cold, right? The reason is because the actual— the slower the fan is going, the more time it has over that coil, the more it dehumidifies, and the cooler the air feels. That make sense? So the slower the fan, the more time it has over the coil, and the cooler the air will be because it's extracting more heat and more humidity out of the air. Than if it was on speed 5 at high. Make sense? So that is why you need a properly sized unit for your house because too big, yes, it's cooling the house down quickly, but you're going on, off, on, off, which therefore is affecting your electric bill because the most power the unit pulls is on startup. So you want it to run a long time. You don't want it cutting on and off. As well as you're fitting the motor and the board, and everything in the unit is not made to go on-off, on-off. It's made to run for a period of time. It's just like miles per gallon in your car. Obviously, it's more efficient to go on the highway or interstate than it would be to be in stop-and-go traffic. You get more miles per gallon if you go on the interstate than if you live in the city. Same principle with your unit. It runs efficiently the longer it runs, and it's made to condition that space. So if the unit is too big, it's going to be on and off, on and off. And if we change out a unit and it's not matching up to the existing duct system, it doesn't matter if we put a 20-ton unit out there. If you get a 3-ton duct system, it's only providing you 3 tons of air in the house. Make sense? So the unit cannot be bigger than the duct because it would do no good.
I have a Carolina room that has 3 glass walls. Our ceiling fan does not cool the room efficiently. What would you suggest?
In that situation, if you don't want to change the unit or the duct system, I would add a mini split in that. Carolina room. Another thing you can do if your unit is of age is to redesign the ductwork and actually do zoning so you have a sensor in that room and it can heat or cool that room to that specification. Otherwise, I would do a mini-split. Some people— I went to a lady's house one time, she was like, "We're just going to build this Carolina room." She actually had a southwest exposure, which is the worst exposure you could have for heat. And she's like, I just want 2 runs to be tapped into here. I said, where's your thermostat at? She said, it's in the hallway of the house. I said, there is no way in this world that thermostat in the middle of your hallway is going to know what temperature it is over here at the sunroom. It's not going to happen. You're not going to be comfortable. She said, "Well, I just want 2 runs tapped in." I said, "Well, why 2 runs? Why not 3? Why not 4?" So these rooms are hard to heat and cool because of the exposure. So they're better off adding a mini-split to it where you have a ton, half a ton system in that room. Or even better, if you have the room, is to zone that. That would be a zone by itself. You have a sensor in that room, just like a thermostat, that would control the temperature in that room. Because on the southwest corner, okay, this sunroom needs to be on if it wants to be 75 degrees on a 90-degree day. The north side of the house bedroom probably doesn't need as much cooling as the southwest side of the house. Does that make sense? So mini split or zoning would be a great way to do it. A lot of times you can't do zoning because of how that room is built or if you have the attic space to get duct over there or under the house. So usually mini split is what we go back with. All right, that's it. Was that good?
That was good.
Very informative.
Awesome.
All right, that's episode 65 of the Ask Derrick Cole Show. Make sure you hashtag all your questions #AskDerrickCole. Facebook, Twitter, and Instagram, and we'll get them on the show.
