I have a space heater to heat the room to about 75 and the rack stays at a constant 80-82 cool side. Except the breeder tubs when the temps drop on the hot side the cool normally drops to 77ish. Also at night i have a blanket (thick) that covers the front of the tubs and also keeps heat in at night.
I do know people who have rooms in the 60's and they use a supplement side heat to keep ambient temps up.
Also I would like to add we don't run the heat at my apt and heating just my room is a money saver vs using the big apt a/c heater.