New tank needs a heater...but what size?

[Scythanith]

I have about 330g of total volume and run 3 x 250w ebo jagers. They are on about half of the time but the back fishroom is pretty warm so there isn't a lot of heat loss there. I let the profilux control the heaters. They also have their own internal cutoff but I set it about a half degree higher than the profilux cut off. A little redundancy never hurt.