Heater wattage vs tank size

[Opus]

What is the rule for heater wattage vs the size of tank? I have a 75gal tank and I know the heater is too small for it. I think I have a 75 or 100 watt in there now and it struggles in the winter to keep the temp at 77 since I keep the house at 68. I was thinking of replacing it with a 150 watt but wasn't sure that would be enough wattage.

 

[FranktheTank]

I believe it's 3-5 watts per gallon.

Burr!! You keep your house at 68 in the winter???

 

[melev]

3 watts per gallon, divided across two heaters. 75g needs 225w of heat. I would use two 125w heaters. If one fails (usually in the on position), it won't have the juice to cook your tank like a 225 / 250w could.

 

[Opus]

I really don't have the room for 2 heaters. I have an AC3 so I plan to have it turn off the heater if it gets too hot.

 

[DaveG99]

if you get the right tyoe of heater they are very small.

 

[melev]

@Opus wrote:

Another thing you can do (that's a great solution by the way), if your tank gets too hot, have it turn off the lights.