it really depends on how warm the room is and how much above room temp you need to heat the water
^^^ This. One formula I've seen online that takes this into account is:
HEATER MATCHING FORMULA: (© Carl Strohmeyer)
As for heating requirements, I recommend 25 watts of heater for every 10 degrees of ambient temperature per 10 gallons you need to raise your aquarium temperature.
EXAMPLE: If your home is 68 degrees and you have a 40 gallon aquarium, to reach a temperature of 78 degrees you would need a 100 watt heater.
As for heating requirements, I recommend 25 watts of heater for every 10 degrees of ambient temperature per 10 gallons you need to raise your aquarium temperature.
EXAMPLE: If your home is 68 degrees and you have a 40 gallon aquarium, to reach a temperature of 78 degrees you would need a 100 watt heater.
I run two heaters that I originally chose using the heater manufacturer's wattage recommendations. Since I only looked at the tank temperature during the day I assumed everything was fine. It wasn't until I got an Apex that I saw that the tank temp was dropping overnight, and realized the heaters were actually undersized and couldn't keep up when the furnace turned down at night.