In this instructional video, Derek Cole explains that installing an HVAC unit larger than a home’s calculated cooling load is counter‑productive. He walks through the load calculation process, showing that a house needing a 3‑ton unit will suffer if a 5‑ton unit is installed. The core issue is inadequate dehumidification: an oversized unit cools the space quickly but cycles on and off, never running long enough for the evaporator coil to remove moisture, leaving the indoor air feeling clammy despite a comfortable temperature. Cole uses a car‑air‑conditioning analogy to illustrate how slower fan speeds increase coil exposure time, extracting more heat and humidity, and how longer run‑times improve fuel (energy) efficiency, just as highway driving beats stop‑and‑go traffic. He also notes that frequent start‑stop stresses the compressor, motor, and control board, raising electricity costs because the highest power draw occurs at startup. Finally, he stresses that the HVAC unit must be matched to the existing ductwork; a 20‑ton unit cannot deliver more than the 3‑ton capacity of a 3‑ton duct system. Overall, proper sizing ensures effective cooling, humidity control, energy efficiency, and equipment longevity.
Chapters
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 of— 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. It's 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 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 affecting the motor and the board. 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.
