Just bought a house with a passive air exchanger: no internal fans, just motorized dampers moving air with the furnace fan. We have a thermopump, electric furnace and whole house bypass humidifier.


My air exchanger has this wye right after the "Fresh air to house" with a damper that dumps right next to the furnace. It looks like a cleanout? It is simply a register for this room?

Should I leave this open or closed? When and why?

air exchanger wye

(This question is split out from but loosely related to Air exchanger stale exhaust too restrictive? Some other issue?)

  • 1
    An electric furnace will not need combustion air, so having it open/close will be more of your choice. Can try each way and see if it makes a difference.
    – crip659
    Nov 25, 2023 at 14:42
  • @crip659 Ah! I hadn't considered that it would be fresh air for a combustion furnace, as this system was installed after the oil furnace was removed. Thanks.
    – msanford
    Nov 26, 2023 at 0:01
  • 1
    I am just guessing, but it does look like a damper is installed, so closing/opening/adjusting is easy. It should be in the close position right now, according to the damper handle position.
    – crip659
    Nov 26, 2023 at 0:29
  • Indeed there is a damper, which I kept closed. I think it's a very logical guess.
    – msanford
    Nov 26, 2023 at 2:56


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