This is on my list of lists:
- Do I need a make-up air inlet? Can I open a window instead? Will I always remember to open a window before I turn on the fan? What if I install a cat door? Can enough air get in through it?
I obtained this 180 CFM exhaust fan to help with moisture and oxygen, based on recommendations I found for the square footage of the room. Later, I was reminded that in SIPs construction, you get a really airtight envelope, with only a little passive leakage around windows and door. Not only does that make getting air hard, it puts strain on places where there’s an air barrier, like caulked crevices for example.
I read that this requires a make-up air intake, and that makes perfect sense.
What does not make perfect sense is that I can’t find any with a capacity greater than 30 CFM. If air is getting sucked out at 180 CFM and can only get in at 30 CFM, is that really helping all that much?
Maybe I should return the fan for a smaller one. I liked that this one was supposed to be the right size for my space, but maybe that estimate is based on standard framing and sheathing. I also liked that this one comes with its own switch. Others have switches sold separately.
However, this one has a switch that has only on and off, no high / medium / low. Separate switches have a range. So maybe it’ll be better anyway, being able to turn it down.
I still wonder about the cat door. See, have a look at this vardo. I could do one of those on the back end of my build. Instead of a chicken cratch, it would be a cat cratch. And a cat door could serve the dual purpose of letting the air in.