Bathroom Exhaust Fan
Condensation:
If you could help me with a
problem, it would be appreciated. There are 2 bathroom exhaust fans
in the house. When it gets below freezing, on one of the fans it
appears that the humid exhaust air freezes in the exhaust pipe and
when it warms up, melts and gets into the ceiling wall board and
puddles in the exhaust fan cover.
The installation of the fan is as
follows: The 4" exhaust fan pipe is attached to the fan and
extends upward through about 8" of insulation goes about
another 5" and then angles away from the roof for another
5." The other exhaust fan has not problem and is vented
straight up.
Are there any techniques to avoid
humid air from freezing in an exhaust pipe?
Martin
Here
in Northern Michigan most houses have bath fan exhaust ducts that
run horizontally to the outdoors. This way the duct is kept warm
so the humid air never has a chance to condense (or freeze) until
it exits the building.
Therefore, I believe the best
solution to your problem would be to wrap insulation around the
fan ducts in your attic. There are long strips of fiberglass
insulation sold just for this purpose. The insulation is wrapped
around the duct and secured with tape. I have also seen duct
insulation that is a sleeve that slips over the duct. This product
has a plastic sheet over the outside. However, this is intended to
be installed during assembly of the duct work... you could use
this product if you disconnected your duct in one location.
Actually your question pointed
out a potential problem in one of our projects. We recently
installed two bath fans and the ducts travel through an
un-insulated attic. We will need to go back and add insulation to
prevent the problem you have experienced.
Bruce W. Maki, Editor.
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