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I have lived in this house several years now. It’s two stories with a basement, two zone HVAC. Trane system less than 10 years old.

I have a register that blasts so much air, it’s completely nuts. But I’m the winter I don’t mind because it is on the first floor, and it’s right under the master bedroom, so if it’s just blowing out heat, that heat goes upstairs where it needs to end up. And we are in Minnesota, so I probably don’t notice it as much with the AC, but when I do notice it, I realize it’s really just blasting a bunch of cold air into a part of the house that’s not used much.

So I took a look at my ecobee thermostats and noticed that that register on the first floor is in the second floor zone. I just noticed that today. And I put it together with the fact that this particular register is sitting right above the HVAC system in the basement. I had planned to put one of those scope cameras down the register to examine where the baffles were and why this register is connected to the wrong zone. But if what I now suspect is true I think it’s OK for me to cover this register. And I know that covering a register is generally a bad idea, in a properly balanced system.

So on the second floor, I have nine registers. And as I say, they are in a zone with one register on the first floor. And the first floor register sits right on top of the HVAC system. So what I think is that the path of least resistance is that one register, and more air goes out that register, and the correct amount of air is not making it upstairs. So blocking that register just lets all that air come out these nine registers upstairs where it’s supposed to.

I have tried to get an HVAC guy out here to look at this. But when I tell them I just want them to explain how these zones work, and help me understand why I have an uneven air flow, they tell me that they don’t have guys to do that, they can’t have a truck just sitting while someone does a consulting job. I told him I would pay them their hourly rate, and they replied with something about it’s not a big enough project. Oh, and when I say I’d also like them to see if my ecobees are wired in correctly (even though I’m 99.9% sure they are), that definitely sends them packing if they had any hesitance before.

I guess I’m asking if this is ok. And if it’s maybe, is there some way I can determine if this is an unhealthy/unsafe/risky restriction?

And also, if I did get a pro out here to look, what should I expect them to do?

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  • do you have access to ducting
    – Traveler
    Commented Jul 26, 2023 at 4:37
  • @Ruskes Yes. I can see almost all of it. I can see all of the attic (if I move 2’ of insulation). And can see half of the downstairs because the basement is partly open. I feel like I can see the critical areas.
    – jqning
    Commented Jul 27, 2023 at 2:04

1 Answer 1

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I don't think blocking an air output is such a bad thing.

Forced air furnaces have registers and the registers have closeable grills and baffles that allow you to close off entire sections. The return air to the furnace isn't changing in size so you'll always have enough air coming back. Your furnace will likely have to work a little harder to push the air up higher into higher resistance registers but so what. It isn't like return air registers typically even have any adjustable flow baffles so I really don't get this general don't block registers it is a balanced system line.

On an HRV where you have adjustable input and output wall caps and you are trying to push the same amount of air as you are pulling and the sizes of each input and output return are calculated and it is a true balanced system I can see not wanting to close off a register but even then you'll just get decreased efficiency.

I had my hvac guy come out and close off two vents. He didn't seem to think much of it and didn't bring up any glaring problems - this was on a system that was in a 1920 house which maybe had a forced air oil or coal furnace originally and was eventually replaced with natural gas. The return air ducts were just the open stud cavities that lead to open joist bays for air returning from the top floor to the basement or mainfloor to the basement.

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  • I would not completely block it but restricting most would give your a good balance.
    – Gil
    Commented Jul 26, 2023 at 19:21

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