Finding the problem
1 of 1
The cause of condensation
Moist indoor air
a cold, uninsulated
duct and water runs down into the fan.
Water stains on the ceiling around your bath fan may indicate
a leak coming from the vent cap on your roof, but condensation
is the more likely culprit. If bath fan ducting isn’t
properly insulated, the moist air from your house will condense
inside the duct.
The first step is to head to the attic. You may find that the
insulation simply needs to be refastened. If you see that your
duct isn’t insulated at all, pick up duct insulation at the home center. Use zip ties or
aluminum tape to fasten the insulation.
If your ducts are properly insulated, another
potential cause of condensation is lack of use.
Bath fans have a damper designed to keep the
outside air from entering in through the fan, but
that valve doesn’t stop warm air from escaping. Whether
you use your bath fan or not, some warm air will still escape
into the ducting. On very cold days, that warm air is likely
to condense inside the ducting, especially if the fan is
never run to dry it out. Guest baths are particularly prone
to this problem.
The bottom line: Before you climb on the roof to look
for leaks, make sure your bath fan duct is insulated, and
run the fan more often and for longer periods. Switches with built-in timers are available.