I had a oil-filled heater that heated my guest bathroom that was my first snake-room.
When it finally did get cold here this winter(all four days of it?) I turned one on in the currant snake room too. Just to give the rack heat a little boost.
It kept the snakes perfectly in my opnnion. The room stayed hot, and humid, and I loved it. I hate the cold. I bet I had the cleanest snake racks ever. Always was in there.