for Cold Climate Housing and much more

Last Updated: , Created: Thursday, October 14th, 1999


The best household ventilation system is a constant operation fan powered balanced air-change system -- a central system that sucks stale air out an exhaust duct and blows an almost equal amount of fresh air into the house through an intake duct. These systems will usually require a heater on the fresh air duct to take the chill off of the winter air (less than 1000 watts is so Mickey Mouse as to be useless). One common version of this balanced air change system includes heat recuperation devices which use the heat from the exhaust air to pre-heat the incoming fresh air called HRV's or Heat Recuperation Ventilators. The addition of heat recuperation to a balanced air change system is expensive, does not always totally eliminate the need for an electric pre-heater and is not always financially justifiable in the milder regions of Canada. (See HRV in the database.) Such a system (with or without heat recuperation) will completely satisfy the need for a planned-hole-high-in-the-house.

The next best system is the installation of one or more constant operation exhaust fans (bathroom fan, kitchen fan, or central exhaust fan) combined with a controlled cold-air inlet. (search the keyword "ventilation" for the title "WHAT IS A CONTROLLED COLD-AIR INLET?") Most manufacturers of these exhaust systems never talk about the controlled cold-air inlet and in omitting that detail they are leading you down the garden path toward cold drafts, colder walls and frosted window and door frames. (search the keyword "exhaust fans" for the title ARE WHOLE-HOUSE EXHAUST FANS WORTHWHILE IN A COLD CLIMATE?)

If you don't want to go to the expense of installing some central system, try using existing holes. A hole 10 centimeters in diameter (4 inches) will maintain a high neutral plane and planned air changes in most houses. If you have vents and/or chimneys, start by closing off or putting dampers on all large or unnecessary holes. Leave open only the most convenient candidate. You will probably lose too much heat up the fire place chimney, so if you have an alternative, use it. An upper-floor bathroom exhaust fan is probably the best candidate -- but you must jam the damper open (and possibly put in a bug screen). If this fan is on the upwind side of the house in winter do not use it. If you must make a new hole, try to avoid going through the ceiling into the attic (don't create more moisture leaks into the attic if you can avoid it). The easiest technique is to go horizontally through the wall near the ceiling on the end of the house away from winter winds. A duct must be put through the wall and sealed carefully to the drywall on the inside to prevent humidity from getting into the wall and sealed carefully on the outside to avoid rain from getting into the wall. Install a grill on the inside and a hood to block rain and snow on the outside. A vent the size of an ordinary brick is easy to find and quite adequate for brick facade houses. Remember, this is an exhaust duct -- it won't freeze the room it is in as long as it is on the downwind side of the house.

If the wind in your area is strongly unpredictable, then you will need your planned-hole-high-in-the-house to be in the form of a chimney (a real one or a dummy ventilation chimney) that goes straight up rather than being on one side or the other of the house.


Keywords: Condensation, Moisture, Neutral Plane, Exhaust Fans, Ventilation

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