On Fri 02 Oct 2009 11:10:46a, Alfred K. told us...

On Thu 01 Oct 2009 09:36:50p, Alfred K. told us...

An exhaust fan has been added to the upper floor bathroom. The attic's
insulation (cold climate!) is blown cellulose particles. Is it
customary to cover the fan's top housing with some kind of a cap to
protect it from being contaminated with the insulation dust?

You should *not* be exhausting bathroom air directly into the attic.
There should be a duct (preferably insulated) connected to the exhaust
fan and connected to an appropriate exterior vent through the roof,
eave, or sidewall of the house. This would also apply to exhaust fans
anywhere in the house; e.g., utility room, kitchen, etc.

An insulated duct, of course, is there, connected to an ridge vent on
the roof. I am asking about some possibility of contamination even with
the duct present.

If the duct is sealed to the exhaust fan outlet, I can't imagine how dust
would enter the system from the attic. You could, of course, seal all
perceptible joints, corners, screw holes, etc., on the housing with duct
tape.

We had a similar installation in a previous house with similar insulation.
Nothing additional was required and we had no problem.

Was it in the area with very hot summers? I am thinking of potential
overheating if the fan housing is sitting deep in the cellulose without
any air gap surrounding it.