Backyard Aquaponics
A place to discuss aquaponics

I wanted to see what experience those of you with indoor systems (in a building, not a greenhouse) have had with humidity. I have two possibilities for placement of my upcoming system. One in a climate controlled mother-in-law's quarters (will keep the mother-in-law away ), and one in my garage. Winters here get down to freezing regularly, and can get even colder, so I'm worried that I won't even be able to keep the FT to a survivable temp for my tilapia in the garage. My biggest concern is that doing this in the climate controlled building would create a lot of trapped humidity and damage the drywall or the acoustic ceiling tiles.

You will definitely need some way to keep the humidity off the walls unless you have some non-permeable surface layer and no penetrations on your walls. Some folks (one in Alaska that I recall) have had real disasters. Best options: cold water fish or keep the walls/ceiling/floor sealed off with plastic. Maybe even leave some air space for air circulation to take care of what moisture does get through.

I keep a couple large aquariums going with tropical fish all year long inside of the house. In the winter the inside temps are normally kept around 65F while the tanks are 82-84F I top up a lot in winter due to evaporation from both the temperature differential as well as in winter Cold High pressure systems keep the humidity down. Your problem areas will be the window sills as the humidity will want to condense on the window panes.

Yeah, I've had multiple fishtanks in a room and had to deal w/ that during winter too. The window frames and sills would definitely be a big issue. I would have to block them all off w/ plastic from the inside I would imagine, very well. I'm worried more about the contant high humidity soaking into the drywall and especially the acoustic tile ceiling...that's basically just pressboard, and cheap pressboard at that. I'd hate for the ceiling to come down (even though I want to replace it..heh). I considered venting the area, but I'd be venting out all my nice heat and it would cost a bundle. There's also dehumidifier units I could use, but there's no telling how many you'd have to have to keep up with that kind of humidity.

I'm assuming that that your source heat will be dry anyway- that will help offset the excess moisture the fishtanks release- topping up fish tanks in the wintertime is a constant issue. The size of your tank may make the difference though so sealing with plastic or using bathroom type greenboard will prevent mold, which is a greater issue than the moisture absorbsion. That can be unhealthy for you and possibly toxic to the fish. Possibly double up on the plastic, with a 4" or more gap between the layers- the dead air space in-between will actually create a micro-circulation system between hot and cold, keeping the majority of the moisture away from the walls but do plan on some sort of ventalation/dehumidifier or you might feel like you're in a sauna.