What you say, a final answer to the age-old question - can air conditioning (and heat) exit through a bathroom vent?
Well, in a word YES!
But even if you already knew that, here is proof!
After seeing what is in this photo, I had to prove it to my client.
That bathroom vents its exhaust into the attic space.
You can see that this is a fan added much after the house was built.
During that era, if a bathroom had a window it was not required to have a vent fan.
Someone thought to add it later. You can see from the cropped photo on the left that it was installed and tied directly to the plumbing vent.
Perhaps it was installed by the same person who thought to add extra insulation, also incorrectly, to the attic!
How do I know it's sucking out air conditioning?
Because toilet paper is sticking to the bath vent grill, but the fan is not on!
There is dust sticking too!
That means the stopper door inside the fan is broken or wrong.
And that exiting air represents a pretty solid stream of energy loss for the house!
And all the time! Winter and summer!
This is a big deal.
Now, during showers, when the fan is on, all that moisture is entering the attic space.
In winter it is warm moisture, added to a cold space.
In summer it is cool moisture, added to a hot space.
Mixing hot and cold like this creates condensation!
What does such condensation do over time?
The left photo is the roof sheathing right where that tube is pointed.
There were four or five different colors of such "fuzz" on the roof sheathing in various locations!
And the rusty metal plate connector for the roof trusses is nearby as well.
In fact, all the metal plate connectors were rusty! That represents A LOT of moisture over a long period of time!
This has been a long-term problem!
My recommendation: houses are composed of many systems! These systems interact! A failure in one can cause failures in others! A problem with one can create problems with others! The house has to be looked at in terms of how EVERYTHING interacts. When such large systems are not installed properly, or "remodeled" improperly, it affects the house very negatively, including the house's life span. When properly installed and properly maintained these systems work in conjunction one with another and the house works long term! I recommend the latter.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560