Well, most aquarium heaters have a little thermoswitch built in, so I doubt he's actually heating- heater won't kick on in a warm res.

Evap cooling will generally keep res a few degrees cooler than ambient.

I'd prob be cooling the room enough to keep res ~70F-, but if that wasn't an option, then yeah, I'd be cooling the res.

Grab a floating thermometer from the pet store and drop it into the res- easy enough to know for sure.