Can mice get through air vents in a house? Yes — and I see this all the time. It’s not the vent that’s the problem. It’s the gap under the vent. Even a small opening is enough for a mouse to squeeze through. Once they’re in, they’re in your walls. Go outside right now and check your air vents. If you see a gap like this, it needs to be sealed. I fix these all over Guelph, Kitchener, Waterloo, and Cambridge. Message me if you’re seeing this at your place.