When the central air is running, cold air blows outside through the intake and exhaust pipes from the HE furnace. Is this normal? Can I block/seal off these pipes for the summer and uncover them before we use the furnace for heat in the fall. Or is there something wrong with the system?

  • Both pipes are exhausting cooled air? How would you describe the volume of air moving?
    – isherwood
    Commented Jun 18, 2018 at 18:47
  • There aren't typically dampers on those pipes, so it's possible that some conditioned air will blow out, especially if the locations and settings of the air ducts and returns creates higher pressure in the vicinity of the air handler. As isherwood asked, people will need to know how much cold air is coming out. It would also help to know locations of ducts and returns, what's open and closed, and other factors that would affect room air pressure at the air handler.
    – fixer1234
    Commented Jun 18, 2018 at 21:30
  • There isn’t any visible dampers on the 2 black pipes - intake and exhaust. It’s not blowing very much but definitely cold air coming from both when the air is on. Volume wise It would blow a light match out. They vent outside roughly 30 feet from the furnace. Will it hurt anything to just block them for the summer?
    – John
    Commented Jun 20, 2018 at 14:36

1 Answer 1


Cold air should not be blowing outside.

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