Winter (Midwest) especially and on windy days air blows strongly out of the Intake vent of the HVAC system when the system is not running. (no fan) With system running all runs normal. When system cycles off the cold air rushes in an chills the room.

What kind of heating system do you have?

Is this a through the wall system like a Mitsubishi? https://www.acwholesalers.com/Mitsubishi-Air-Conditioners/MSY-GE15NA-14000-BTU-21-SEER-Ductless-Air-Conditioner-Air-Handler/19572.ac?gclid=CLGi9aGk48UCFdcegQodbXQAow

What kind of heating system do you have?

Ruud quiet 80

I read many interesting articles on your problem and thought this one was the best,

ASK THE INSPECTOR: Furnace new, but outside-air intake useful - Winnipeg Free Press Homes (http://homes.winnipegfreepress.com/winnipeg-real-estate-articles/renovation-design/ASK-THE-INSPECTOR-Furnace-new-but-outside-air-intake-useful/id-1926)


While not absolutely necessary, a properly insulated fresh-air intake duct attached to the return-air ducting for the heating system is a good idea to maintain healthy indoor air quality in your home. If you find too much cold air coming in or the return-air ducting frosting up, installation of a mechanical damper on the intake duct connected to the furnace fan control will help limit the air intake until it is needed.

Let me know what you think, as this is a very common issue.

Thanks for the info. I had that problem with a previous unit. My apologies if I have not provided accurate info. The return air vent from the house is more accurate to where the air is being reversed. It's windy out today and air is blowing into the room from the return vent with the unit off. It seems that the air is coming down the flue thru the unit and into the ducting (both return and conditioned). Is there such a thing as a damper for the flue cap or such? Thanks much.

Yes.

Air-mixing plenum - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Air-mixing_plenum)

You have a leak in the return. Crawl under the house and look at the ductwork for the return. If you have ductboard the company screwed you to start with and possible rats chewed holes in it. If air blows out of the return while it's not running there's an open spot in the return. It's all sealed ductwork and the only way for that to happen is to have an open spot in the return.