Just put one of these Via Aqua 300W Titaniums in the 38G tank I keep below my 150G Bowfront. Also have a FX5 running in it and a Rena 400 pumping 70* air into the tank This thing keeps everything at 78* no problem.
Only reason I went with one of these is because I bought a 50W one over 10 years ago and it still runs like brand new.