What explains ever-changing weird smells in my basement?

December 25, 2021 10:34 AM

I have a damp basement and it normally smells musty. To control the mustiness, I set a dehumidifier at around 40% humidity. The unusual thing is that the smell often mutates into different flavors (sometimes very acrid, sometimes disappears altogether), though the humidity is constant and there's no other changes I detect. The only hypothesis I have is could be different breeds of mold growing for random reasons (?) I'm just looking for any other plausible explanations...
posted by Jon44 to Home & Garden (10 answers total)

Do you have floor drains whose traps might be drying out, allowing sewer gas in?
posted by likedoomsday at 10:59 AM on December 25, 2021 [3 favorites]

Response by poster: ...there is a floor drain and I never heard of this issue before. Thanks.
posted by Jon44 at 11:29 AM on December 25, 2021

It's worth trying that. I dump a bucket of water down my floor drains every week or two. I'm told that putting mineral oil in the drain can help prevent evaporation, but I haven't done that (and am not sure how much to use or anything like that).
posted by likedoomsday at 12:15 PM on December 25, 2021 [1 favorite]

If you have to pour a bucket of water down your floor drain that often,you really want to install a backflow drain valve. They only cost a few bucks, are very easy for non-experts to install, and will make your life materially better.
posted by mhoye at 3:09 PM on December 25, 2021

I don't know if I have to, I'd just rather overdo it and never have the sewer gas smell than only do it when the smell tells me I need to. But I'll look into that.
posted by likedoomsday at 4:05 PM on December 25, 2021

If you put RV antifreeze in the floor drain it won’t evaporate and is safe for plumbing, sewers, etc
posted by rockindata at 8:17 PM on December 25, 2021

Sometimes water that disappears from a drain U-trap isn't doing that because of evaporation. Depending on how or even whether the drains are vented and what the wind is doing as it goes past the nearest vent, it's possible to get enough of an air pressure difference either side of the U to suck a little of the water down the drain, lowering the level of what's left in the U to the point where it doesn't maintain a reliable gas seal.

Replacing the U bend with a deeper one will fix this, but like any modification to drain plumbing that involves excavation and floor repair. If this problem were my problem I'd just dump a bucket of water down it periodically and live with it.
posted by flabdablet at 10:17 PM on December 25, 2021 [2 favorites]

I mean... are you looking for other possible causes for basement smells? Mice nest comes to mind. Hope you get this all cleared up.
posted by slidell at 11:59 PM on December 26, 2021 [1 favorite]

Can you hook up a discharge hose to your dehumidifier instead of the tank? I did with my basement dehumidifier and ran it to my floor drain, now I am dehumidifying and my floor drain never goes dry and no dumping the tank!
posted by AzraelBrown at 8:32 AM on December 28, 2021 [2 favorites]

Response by poster: @AzraelBrown
I do have this already set up (discharge hose from humidifier goes to drain). I assume when things are dry, there's not enough output to keep the trap filled (especially as the dryness must speed up evaporation of water that was there).
posted by Jon44 at 1:24 PM on December 30, 2021 [1 favorite]