I'd think that as long as your room is in the high 70's/low 80's in temp, you'd only need the flexwatt on ONE end of the tub. The room temp of 80 could quite easily be your cool end, w/the flexwatt providing the hot side. That's how I've got MY tubs set up right now.

Unfortunately for MINE, it's the room itself is getting TOO hot occas. and I've had to UNPLUG the flexwatt in order to keep the snakes COOL enough.

Sheesh!

R