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Ventilation to cool down poorly-insulated house

My wife and I recently bought an old (1880's) two-story duplex with separate apartments on each floor, each about 750 square feet and very poorly insulated. We have long-term renovation plans, but our primary near-term complaint is the inability of the apartments (especially upstairs) to cool down at night -- even with our quite cool summer nights here in Northern Colorado and all the windows open. We don't want air conditioning, but we would like to improve night-time ventilation.

I've considered a whole-house fan, but the roof has no soffit vents and only one small static vent at the peak (hip roof on all four sides) -- not enough (I think) to support a whole-house fan without making some changes to the roof (money tight right now). The floor plans in both units are not very open, either, which I think is preventing natural cross-ventilation via windows. Ideally, each apartment would have some individual control over the degree of ventilation.

I'm thinking maybe a window-mounted exhaust system -- or, perhaps, a robust bathroom exhaust fan (or maybe the two in tandem?). The upstairs apartment bathroom needs an exhaust fan anyway...

Does the GBA community have recommendations? Suggestions for particular products? Appropriate rate of air movement? Any help very much appreciated. Thank you.


Asked by Kevin Ummel
Posted Thu, 07/24/2014 - 19:36


1 Answer

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This is the type of question where ordinary common sense can work fine. If the occupants of the apartments are willing to open their bedroom doors at night, one bedroom can have a window-mounted fan that blows inward, and another bedroom can have a window-mounted fan that blows outward.

If the bedroom doors must stay closed at night, the same strategy can work in each bedroom, as long as the bedroom has at least two windows. It's possible to pursue this strategy with just one fan per bedroom. If a window-mounted fan is operating, the second window will either provide makeup air (if the fan is blowing out) or will provide an escape path for exhaust air (if the fan is blowing in).

A bathroom exhaust fan is unlikely to provide enough cfm to significantly cool the interior of the home.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 07/25/2014 - 06:23

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