It's probably just fine. Snails tolerate a much wider range of temperatures than do tropical fish. Some species (e.g. MTS) won't breed as easily in cooler water.
The snails that make their way in with plants can survive in an unheated tank, as so can mystery snails. We have put numerous ones in our pond before, and I breed the small little ones and the trumpet ones for food for the puffers and loach.
I raise trapdoors outside year round here in East Tennessee.
Generally, it gets into the single digits F several nights during the winter.
So, they should do just fine in an unheated tank inside a house.