Watt Size Aquaruim Heater?

[BrentonSpear]

I will have my fermenter in a tub of water and I want to get an aquarium heater to heat the water.

I would think there would be a max of 5 litres of water to heat.

Is a 50 watt heater big enough? 100 watts?

What are other people using?

 

[Nearly]

I have used a 100w aquarium heater and it was more than ample. I put it on a timer to only run for a half hour every hour and a half and it kept the brew at 20-22 deg while it would have been down to about 12 deg if no heater.