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I have a draft occurring in my 2 story home, usually on windy days. The main floor is fine, but in the master bedroom on the second floor, there is cold air entering the room from the air return vent. It's not much, but noticeable. In the basement (which is finished), cold air is coming from the heat registers, quite noticeably, and when the furnace isn't running.

I've made sure that all the obvious sources for drafts are sealed (doors, windows, etc). The house is ~15 years old and the heating system is forced air.

Can anyone suggest where this air might be coming from?

4 Answers 4

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Are you sure the air is coming from the return vent ductwork itself? It's not coming from the edges of the vent where the ductwork is attached to the vent?

I would hypothesize that on windy days, your attic is becoming pressurized by air entering via soffit vents or roof vents that are on the windy side of the house.

Air would need to escape to the lower pressure areas wherever possible. In theory, this would be vents on the downwind side of your house. But if there are air gaps where ductwork meets a vent or where a ceiling light fixture goes, those would also be ways to equalize the pressure.

If your attic were becoming pressurized like this, you'd probably notice a large gust of air coming from the attic if you opened the access door to your attic.

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Air is penetrating the walls and getting into the ductwork, or there's a gap in your heat exchanger which is potentially deadly.

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This could also be caused by bad/torn/loose ductwork in the attic area. I would check the return ductwork in the attic for tears and/or breaks.

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The same thing happens in my house. It is single story and has two hall return grills. All the ducting is installed in the attic space. The larger of the two ducts is longer distance to the return plenum. I believe the air just cools down inside the duct after the furnaces call is satisfied and by nature it flows out and down. I think that warm air from inside the house at the ceiling may displace the air coming out. I can feel the coolness on my head when I walk under the return air grill. The other grill Is in a hallway with a higher ceiling and I don't notice it happening there. I also believe that the air could be traveling backwards through the ducting with the small supply ducts allowing the air to flow back through the return air grill. The furnace and all the ducting are basically open airways for convection to occur in the off cycle. The larger grill pulling air from the smaller right through the furnace and plenums and out.

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