Cold draft coming from vents when system is off

dnkr · Dec 13, 2022

I had my system installed about 6 months ago. Now that Winter time is here I started using the heat pump and it works great. The only thing I notice is in one room (master bedroom) the air blows really strong BUT the air coming out of the vent is cold and will be neutral at best compared to the other rooms which are pretty warm.

The other bigger and more worrisome thing I noticed is a cold draft coming out of most of the vents and especially more out of the master bedroom one.

My Hvac company took a look at it a few days ago and said theyll schedule a free air balancing because it was suppose to be done after the install anyway. I dont blame them for rushing out, it was crazy hot in the summer during the installation. I just hope for peace of mind that the air balance will fix this problem or should I be worried about ducts leaking/ripped. (I crawled the attic and took a look and everything seemed fine.Then again, I probably wasnt sure what I was looking for)

rundawg · Dec 13, 2022

dnkr said:
Cold draft coming from vents when system is off

Is the fan selector on the thermostat set to "AUTO" or "ON"?

If "ON" the fan will run when the unit is not heating.

Do you happen to know what the model number of the furnace and thermostat is?

dnkr · Dec 13, 2022

The model I have is Trane 5 ton XR17 Heat Pump + Air
Handler (TPOV) Split System. (2 Stage
cool, 2 Stage heat with XL824 thermostat. It's set to auto. The draft that comes out of the vents is more like one you'd get on an unsealed door or window in the winter, the one in the bedroom is really drafty.

ehsx · Dec 13, 2022

Duct insulation r value?

dnkr · Dec 13, 2022

R-6 value. Here is what the trunk going to the master bedroom and master bathroom it looks like : https://imgur.com/gallery/C162W7T

Both have that similar draft and get neutral air when the rest of the house is heating

ss120396 · Dec 13, 2022

The master bedroom air not being warm is odd, definitely worth looking into. And if you are using it regularly in heating mode and you get a draft immediately when the system shuts off, that's also concerning - seems like there might be a sizable duct leak.

On the other hand, drafts when the system is off for a while are a very common problem for ducts in an unconditioned attic in cold climates, when the system is off for a long time. We see it a lot here on cooling only systems. Insulation doesn't really help because as long as the system is off long enough, the inside of the ducts will eventually get cold. Insulation only slows this process, doesn't stop it. It can even lead to issues with condensation in the ducts when the warm moist air from the house rises into them, and water dripping out the registers. Only way to solve is block of the registers when not in use.

ehsx · Dec 13, 2022

Current code in some areas is min r-8 duct insulation.
Funky looking branch xtions.
Duct leak test and air balance would tell the story.

Cold draft coming from vents when system is off

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