In this video Derek Cole explains why the upper floor of a house often feels warmer than the lower floor and why a single HVAC unit struggles to keep both levels comfortable. He describes the physics of heat rising, the additional heat load from an attic, windows, and the lack of comparable insulation in a crawl‑space beneath the lower floor. Because the thermostat is usually located downstairs, the system over‑cools the lower level to keep the upstairs warm, leading to uncomfortable temperature swings. Cole recommends solving the imbalance with a zoning approach—splitting the house into an upstairs zone and a downstairs zone, each with its own thermostat—rather than installing a second HVAC unit. He notes that zoning works best when existing ductwork can be leveraged, but if a duct chase is absent, retrofitting may be required. The overall message is a pragmatic, cost‑effective strategy to achieve balanced comfort across multiple stories.
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The problem with one unit covering both is that you have different demands upstairs than you have downstairs. So when you look at a house and think about it, heat rises obviously, right? So when heat rises upstairs typically will be warmer than downstairs, right? So chances are, I've seen this before, the thermostat is downstairs. You have a unit that runs the whole house up and down. So to get upstairs comfortable, you then have to make downstairs freezing. When I first got married, we lived in an apartment that was 2 stories but had 1 unit. So I mean, when you went downstairs at nighttime, it was like you better put on like a big coat and everything because it can happen. Because upstairs you have more of a load than you have downstairs. Downstairs, heat rises. You also have the attic upstairs, so you have these forces you're going against. You have the attic, you have windows, you have upstairs heat rises and downstairs, of course, cold air falls and you don't have an attic downstairs. So you— and the crawl space is not that much of a heat load compared to an attic. So it's different demand. So how you solve that problem is either two units or what we've done quite a few times, which is zoning. You make downstairs one zone, you make upstairs one zone. It's very simple. If you have a unit that covers up and downstairs right now, you can very simply make it a two-zone system. That way you have a thermostat downstairs, you have a thermostat upstairs. You can keep it that temperature you want, you keep it that temperature you want, and they can make it work that way. So the challenge with some houses is that there is not that duct chase in the house for the duct to be run to have one unit for the whole home.. But if you already have that, obviously that's available, but you just need to make it a zoning situation. I wouldn't get 2 units. I would just zone it upstairs, downstairs, and that will solve the problem. But until you do that, it is what it is. I mean, the thermostat downstairs, upstairs is warmer in the summertime. It's going to be, so you're just going to have to freeze it out downstairs and Get upstairs as comfortable as possible.
