What did you say - the bath fans huffed and puffed and blew the frosty dew down?
This is a 1970s house, and surprisingly has both original bathroom vent fans operating. But there are no soffit vents, and I noticed no roof or side vent openings anywhere while I was looking at the house outside.
So I was interested in how everything inside exhausts air!
I was not disappointed.
But it was interesting. I saw something I had never seen before.
Looking into the attic space I saw frosty dew distinctly located in two different places.
Frosty dew? How does that happen?
Apparently neither vent has a operating interior flap, so heat from the house makes its way out through the vent openings in the two bath ceilings. Heat seeks cold, and the previous night it was extremely cold. I arrived at the house and it was 15F. During the night it was down to 7F or so.
For lack of a better word, frosty dew could be seen extending from the edge of the roof and making its way up the slanted sheathing. That heat made its way to the edge of the roof and simply rose from there, freezing along its way.
Turning on the fans to make sure they discharged into the attic, as I suspected, an interesting thing happened!
The blowing air gently began melting the frosty dew!
This homeowner had added extra insulation. On top of the 70s fiberglass was blown additional cellulose insulation. A good thing! But it still may have blocked each bath fan's discharge somewhat. Still, the air moves and that evidence can be seen.
Nonetheless, it's always best to vent bathroom air outdoors. In fact, today that is the code.
What was the code in this county in the 70s? I don't know. Apparently to the edge of the roof! With no soffit vents it has no where to go but up and in.
And as warm air gently seeps out the bath vents and crawls up the sheathing, it creates dew, which in this attic, the night before, had frozen!
My recommendation: it's good to huff and puff if you are a bathroom exhaust fan! But it's best to huff and puff that air outdoors. Even if it is not the current code that would be best. It causes less stress to the house and roof sheathing! And doing so is the Best Practice in any case. If you are a wolf and want to huff and puff, may I suggest you NOT go down the chimney. The pigs are waiting.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560