Top of furnace to connect to chimneyReplaced with newer, high efficiency furnace and cold air constantly coming out of vents (except when furnace running). It's like the downdraft is totally free flowing and when windy outside very strong cold air blowing out of the vents. Is there some way to put a vent on the downdraft? Not sure if it's the outer column of chimney for the down draft or the actual exhaust chimney.

Do people put a vent over the chimney part to stop air from blowing back in? (there is a cap on the chimney). How can I put a vent on the downdraft part? Or can I filter it at the top?

  • What is the make and model number of the furnace? Can you post a photo of the installation? – Tester101 Feb 8 '16 at 16:07
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    Typically a down draft (down flow) furnace, is a unit that takes return air in the top, and puts out heated air out the bottom. As opposed to a up draft (up flow) unit, which takes return air in the bottom, and pushes heated air out the top. In neither case should the outdoor air be mixing with the conditioned air. If the blower is always running, the furnace would be circulating indoor air even when the burners are off. If that's the case, you can likely disable this feature. Make sure the FAN switch on the thermostat is set to AUTO, not ON. – Tester101 Feb 8 '16 at 16:12
  • The fan is not running, it is free flow of cold air coming up the vents when the furnace is not running. When furnace is running it is blowing hot air – D Jean Feb 8 '16 at 17:11
  • Is the furnace in the attic? If so, is the portion of the attic where the furnace is, unconditioned space (unheated)? Does the ducting run through unconditioned space? If so, are the ducts insulated? – Tester101 Feb 8 '16 at 17:50
  • it is a single wide mobile. furnace in a closet. chimney up through roof. No drafts around the chimney – D Jean Feb 8 '16 at 18:03

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