I have about 240gal system total volume with 60gal in sump in cool basement. Currently running three heaters in sump (200, 200, and 250w) and they are not keeping up. The heater thermostat settings also don't seem to register very well and they have to be cranked up to temp settings much higher than what setting should be or they keep shutting off frequently. Now that winter is here I am struggling to keep tank warm enough unless I heat the living room where the DT is, 24/7. My wife is loving the warm room but I am scared to see my gas/electric bill. I am running LEDs so no help with heat there.

What suggestions do you all have for a higher wattage heater? I would prefer a single unit and relegate the other heaters to backup and saltwater mix tank duty.