Depends on the rack and its design. Ours are all open-sided to keep them lighter weight and less expensive (we build our own) so we keep the spare bedroom they're located in fairly warm. If you use a rack that is enclosed or well insulated you may the cool side temperatures are ok. If not you can add a strip of heat tape on the cool side, controlled by it's own t-stat, and set it so that the temperature in the tubs stays around 80*F.