Derek ColeGM, Simmons One Hour Heating & Air · AI HVAC Answers

How to Fix a Room That's Too Cold or Too Hot

20 Jan 2023 · 3 min

Watch on YouTube

2:44

In this instructional video, Derek Cole draws on over 20 years of HVAC experience to explain why adding a new room to an existing house often leads to temperature imbalances. He outlines how the original duct system, typically sized for the main house (e.g., a 3‑ton unit), can become overloaded when new duct runs are added, delivering insufficient airflow to the addition and reducing comfort in the original space. Cole highlights the problem of thermostat placement that cannot accurately sense the new room’s temperature. He then presents several solutions: (1) upsizing the whole system to a larger capacity (e.g., a 4‑ton unit) and resizing the main trunk line, combined with zoning that uses separate thermostats for each area; (2) keeping the existing unit but installing a dedicated HVAC unit for the addition; and (3) using a mini‑split system for small additions where only about 1 ton of cooling is needed. The video emphasizes practical decision‑making based on airflow, tonnage, and zoning to achieve consistent comfort across both the original house and the new addition.

Chapters

I can't speak to this specific situation, but I can tell you what I've experienced and what I've seen in the field for over 20 years. So this is the original house, this is the addition. So for the original house, you have your duct system, right? Assuming it's just a standard house, you have your duct system and you have your runs coming off of that duct system. Right? So all by itself. So they said one day we're going to build this addition, right? But we want to put it right here. We're not going to change anything else. We're just going to add those two runs you mentioned in that addition, right? Now, a couple of problems. First problem is that duct system is built, for example, let's say this home is a 3-ton. Let's say this little thing here only takes a ton, ton of air, right? So this 3-ton home is now— you're now sending a ton of air this way. So now it equals 2 tons for this home. It's going to make this to start being uncomfortable, and this is always going to be uncomfortable. You don't have enough air, and the thermostat is probably towards the middle of the house. Well, there is no way that thermostat can tell you what the temperature is in that room. So the existing home will be a problem, but now this is going to also be uncomfortable because you have 1, 2, 3 outside walls. You have 3 outside walls. This space is completely different than this space. So how do you solve the problem? We need a 4-ton unit. And we need what we call zoning. So resize this main trunk line for 4 tons, have that ton of air going back to this room, keep 3 tons of air in this part of the house, right? But we're also going to zone it. So that means we're going to put a thermostat here and we're going to put a thermostat in here. So now this room always has the temperature reading compared to this room. So you do it that way, or you keep that 3-ton. Again, you still have that addition, and you could put a separate— a whole separate unit in that addition. Or you do maybe even a mini-split. That's— if it's only 1 ton, maybe a mini-split works, whereas a a unit, outdoor unit, indoor unit, no duct system, and you're comfortable.