If you dont have adequate insulation on the floor of your attic, there
could be condensation which forms on the roof joists and underside of
the roof deck. An attic fan will keep the air moving in your attic and
help evaporate that to a minimum. The motors on attic fans are
generally in the range of 1/15 th - 1/6 h.p. and thus, draw a low
amount of amperage hence electrical cost. Id go up in your attic and
try to spot condensation on a humid day outside ; if you dont see any,
then id just use the attic fan for summer to reduce attic temperature.

PGG wrote:
During the summer, I had to replace the powered attic fan (which
wasn't even operating) because the wind sheared off the rain lid. I
replaced it with an "all-weather" model that has a humidistat for winter
use because I had a tiny bit of ice-dam like formations last spring. I
live in Wisconsin and have the humidistat set for 75%.

The problem is that right now, it is 95% humid outside with a temperature
of 28 degrees. Of course the fan is running right now, but it seems
unnecessary.

Correct me if I'm wrong, but condensation is only going to occur if there
is a large difference between attic temperature/humidity and outside
temperature/humidity.

So to me, it seems that having a single humidistat in the attic is just
dumb and will run the fan during unnecessary conditions.

Should I just disable the humidistat?


Ice dams are caused by the snow over the eve not melting when the snow
over the rest of the roof is melting. The result is a "valley" effect on
the roof which can collect water. The water then backs up under the
shingles. Shingles aren't designed to prevent water intrusion in this
manner, so the water gets in.

Normally water from ice dams will drip right around the area of the
outside wall.

The solution to ice dams is to improve attic ventilation and insulation.

Do you suspect that your problem is an ice dam or condensation?

Peter H