This is tricky because it is also a downside to tubs. I currently keep my ambient at the right temp by having my snake room at 80 using a space heater with a built in thermostat.
My UTH set at 93 does not heat my ambient up more than .5 to 1 degree above room temperature. So If your house is cooled down to 75 or below you may have issues maintaining correct temperature.
I have seen where some people have installed mettle mesh into the top of their tub lid and used heat lamps with a thermostat to control the ambient.