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Heating & Air Conditioning Home Repair

House cold upstairs, warm downstairs

4 years ago

We bought our house new in 2016. We change our air filters regularly and never had any problems with our AC unit. We scheduled regular yearly maintenance for the first time this July and about a week later our unit stopped working completely. We reset it at the breaker and it would work for a couple hours and then stop again. We had the same company come back out and they told us that the breaker was bad and that we needed to replace it. We thought they messed something up and fixed it without telling us when they came back and just told us the breaker thing to cover it up. Since it was summer in SC we didn't want to test that theory and instead just replaced the breaker that night and the AC didn't have any problems after that. The past 2 weeks I've noticed a stale, damp, mildew type smell downstairs on and off. I changed the air filters again and didn't notice much of a difference. I was researching some possible causes and solutions but ran out of time because we were leaving for vacation.

The day we left for vacation I noticed the downstairs was about 3-4 degrees warmer than the temperature it was set to. I thought maybe it was from us making several trips in and out of the house to load the car. Upstairs was nice and cool. We came back from our vacation and noticed the same problem. The downstairs wasn't hot, just not as cool as it normally is. I checked up in the attic and noticed a hole cut in one of the ducts that was previously covered in duct tape, but that tape is now loose and flapping. I just taped over it with new tape about 30 minutes ago. The attic actually felt cool when I went up there which is not how it normally is. It is normally unbearably hot, even at night. I also noticed air blowing out of the fans in the big box in the attic, which I've never noticed before. We only have 1 unit and it is located outside. the lights in the attic for zones 1 and 2 are both solid green but no air is coming out of the downstairs vents. I don't know much about central air but can follow some troubleshooting steps if I can find some videos. What do I need to look at next?

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Comments (6)

sktn77a
4 years ago
So did you solve your "cool upstairs and warm downstairs" when you re-taped the hole in the duct? Tape frequently stops sticking after a few years - you may need to go over all taped joints to make sure you have no more leaks.
HU-95164968
Original Author
4 years ago
I gave it a few hours and the air still isn't blowing downstairs. I'll go back up and check tomorrow to see if there are any other spots leaking. Is there anything else I should check while I'm up there?
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Just set the thermostats to the temps you want. You want upstairs cool at night for sleeping? Set the up thermostat to your desired sleeping temp and downstairs to high enough so the AC does not run until your program wake time when you have a lower setting. If it gets too warm upstairs, you will just have to find a downstairs temp that allows the upstairs system to keep up. That will be trial and error. If you need to keep some area cool for the cats during the day, choose the downstairs because that will cost you lots less. The cats will figure out that they need to be downstairs to get coolness. Consider improving your energy efficiency so you don't need to run the AC as much. Get an energy rater and find out if you need to seal off your living space better from the attic and other outside air. Find out if you need better attic venting. Find out if more insulation would help.
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Follow-up: I got a full audit with blower door test, which was awesome. Found a number of prominent leaks, some of which I'm plugging myself (supply registers, outlets, windowframes), some of which are for future consideration (basement), and some were plugged when I got my attic sealed and insulated yesterday. It turned out that after my recent roofwork, there were some areas of the attic that really needed to be sealed and insulated, so I am I happy I got that done in any case. Now we will see how the house performs on a hot day, assuming we ever get another one around here. Next on my todo list is probably my horrible supply ducts in the basement for the upstairs supplies (undersized, uninsulated and leaky). But we'll see how things go in the meantime.
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Well you definitely need more insulation. In your area its supposed to be R49 i believe. Where there any obvious gaps in the fiberglass over the attic floor? I would eventually blow in about 6 inches of cellulose over all that to achieve the R49. More immediately are you getting equal air flow from all your vents compared to the downstairs? If its not try to use your dampers (if you have them) to balance it out. Also how many returns and supply vents do you have upstairs? Make sure no returns are covered up by furniture.
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Comments (9)
Go into the attic and inspect the duct work carefully. Most likely it is flexible that could either have a bad kink or leak. This could be a reason why the first floor a sufficient amount of air. See if there are any damper controls for the duct work going supplying each floor. If you are lucky, you might be able to reduce the flow to the second floor and increase it to the first. If you are not able to make any improvement in the attic, then you could close one or more registers on the second floor. Experiment by closing a register that has the strongest air flow, or one that is closest to the attic. Wait a day or two to see if it has made any change in the temperature difference. Don't close too many dampers. That could cause additional problems. If that has no success then bring in an HVAC contractor to examine what you have. You may be able to create separate the system into two zones. But it most likely mean you will have to purchase a 2-stage variable speed air handler and install a second thermostat on the first floor.
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sktn77a
4 years ago
Sounds like a ductwork issue.
branson4020
4 years ago
So 1 unit, 2 zones - you have zone dampers?
HU-95164968
Original Author
4 years ago
so air is coming out of all the spots with red arrows. There's water where the blue arrows are. The teal duct tape is what I put over the old tape last night (all I had on hand) and now there's condensation on the tape. We have 2 zones and last night zones 1and 2 had green lights and today zone 2 is red.
User
4 years ago
Generally, on the HZ311, the red light is a damper closed or closing. So, if Zone 2 is downstairs, then the damper being closed explains it. You should check your home warranty, as coverage for the HVAC equipment might still be in effect for manufacturing defects, at a minimum.

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