What size heater for a 20 gallon?

[AJE]

I don'r have much experience with heaters but I think I'll need one for my future multi's tank. What size heater would I need to heat a tank to 77ish degrees?

[Nate s]

Depends on location. If it’s in a cool basement maybe a 100watt. If it’s upstairs a 50w would be fine. 

[Guppysnail]

I do 2-50w on my 20 long one at each end both near a flow positioned on an angle.  I never have fluctuations but I did have one quit and was great full I had two. How many or what watt you should have I could not tell you but this set up works for me on anything over 10 g

 

ADORABLE Iguana  BTW very striking green. 

Edited June 16, 2021 by Guppysnail

[tonyjuliano]

Useful chart…

the “heats” listed is the amount you are trying to raise from ambient. 
For example, with a 20 gallon tank, if you are trying to achieve a temperature 9 degrees above ambient, it would require 50 watts.  18 degrees requires 75 watts, and so on.

BTW - the dual heater method (lower wattage) is a great fail-safe when heat is critical - as @Guppysnail suggested.

Edited June 16, 2021 by tonyjuliano

[StevesFishTanks]

I use 50w in my 10s and 20s