Size (height/width/depth) - Output (Watts/BTUs per hour)
Sizes:
3 bar 675x675=167W/667BTU 3 bar 675x825=190W/762BTU 4 bar 750x525=169W/577BTU 4 bar 1275x525=239W/817BTU 4 bar 1275x675=266W/907BTU 5 bar 1575x525=292W/997BTU 5 bar 1575x675=327W/1116BTU