Here is the table to help with what size individual heater you need. Delta T is the difference from the lowest ambient room temperature in the room to your desired tank temperature. Always get a heater a little larger than you think you need so just round up to the next nearest size.
Hello, for 55gal I like to use 3×100w. I have them attached to the back bulkhead(2 in corner, 1center) w/spraybar washing over them.
This seems to distribute heat more evenly, if one goes out it gives me more time to rectify situation & 100w is cheaper than a 300. Hope this helps you!!!!!