What the rule of thumb on buying heaters?

[125intx]

I need a new heater for a 30gal. But I would like to get somthing big enough to handle a 55. So there is some room to upgrade later. What is the rule of thumb? 5 wats per 10 gal? Or what?
Thanks!
Chris
PS is also by a north facing window and an out side door.

 

[dburr]

I think it's 5W per 10 gallon, BUT, I don't recommend buying a bigger than you need model. If it sticks, your tank is cooked. I use 2 small ones. If you upgrade later just buy for another 30 gallon heater and run both of them.

 

[viper_930]

I go by 3-5 watts per 1 gallon, so you should be looking for a 150 or 200 watt heater. FWIW, I'd go for the 150.

 

[nereef]

heater size needed depends on how much the temperature difference will be in the room compared to how warm your water will need to be. let's say you have your room at 70 degrees and you want the tank at 80 degrees. this is a ten degree difference. for a 55 gallon to be heated an extra ten degrees it will take about 200 watts. if there was a 15 degree temp. difference you might need 250 watts. i would also recommend getting a small backup heater just in case.
i also would run two small heaters instead of one big one.

 

[rappa]

I would go with a 250 for a 55.

 

[corally]

I bought a bigger heater than I needed for my seahorse tank and could never get the temp low enough. I wanted it at 76 but it always stayed at 80. My house is also COLD, I'm in Ohio and it is about 15 degrees right now, so it's not like the tank was getting heat from the room temperature.