Condensation, Bath Fans, Windows, Etc.
Marc, a remodeling contractor, emailed me overnight about a problem at a customer's house.
He was hired because water was dripping out of a bathroom exhaust fan. The owner wanted it to stop.
It was not a roof leak. It was condensation forming inside the exhaust pipe that collected and flowed back inside the house.
With the BITTER COLD we're having here in the USA, it's to be expected.
Marc had insulated the exhaust pipe but there was still water dripping and he was at the end of his rope. Here's why he's having an issue and it's TOUGH to solve.
Insulation
slows the transfer of heat that wants to move to where it's cold.
When an insulated bathroom exhaust fan pipe is up in an attic for hours and hours overnight where the temperature is 0 F or below, the pipe AND the insulation get COLD.
There may be a little heat
that leaks up through the fan, but believe me the pipe and the insulation get COLD.
When you then turn the bath exhaust fan on and warm moist air starts to flow through the pipe, water immediately begins to condense on the inside of the pipe.
It will CONTINUE TO CONDENSE until such time as
the pipe wall surface temperature rises to or ABOVE the dew point of the moist air flowing through the pipe!
This could take quite a few minutes! It's all about physics.
The same is true for high-quality insulated glass windows and skylights. You can get condensation on them in very cold
weather. It's NORMAL!
It's all about what is the temperature of the glass with respect to the dew point INSIDE your home.
CLICK HERE to read a past column about Condensation. 
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