I am considering building a vent with a fan in my upstairs bathroom that would exit out of the roof. Since the bathroom is in the center of the house it cannot easily be vented to the side of the house, so the roof is the only option I am considering.

The problem is that it gets very cold in the winter here and I do not want freezing cold air blowing down on me through the vent when I am in the bathroom (naked sometimes).

How can construct the vent so that it will not admit cold air during the winter?

  • 1
    The vent should have a damper valve or flapper that is pushed open with the fan. When the fan stops the flapper closes and no back flow from outside. – Ed Beal Jul 18 '16 at 13:59
  • If the building is heated, the colder it is outside the more of a draft up the pipe there will be - hot air wants to leave, upwards - the cold air to replace it will come into the house elsewhere, for the most part, rather than bucking the exiting flow up the pipe. Welcome to the chimney (or stack) effect. – Ecnerwal Jul 18 '16 at 15:31

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