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What Wattage Heater Do I Need For My Fish Tank Aquarium

The best method to work out the wattage of heater required for your home aquarium fish tank is to consider the average ambient temperature of the room and work out how much extra heat will be required to increase the temperature of the water above this.

Tank SizeHeat 5ºC/9ºFHeat 10ºC/18ºFHeat 15ºC/27ºF
5 gal/25 L25 watt50 watt75 watt
10 gal/50 L50 watt75 watt75 watt
20 gal/75 L50 watt75 watt150 watt
25 gal/100 L75 watt100 watt200 watt
40 gal/150 L100 watt150 watt300 watt
50 gal/200 L150 watt200 watttwo 200 watt
65 gal/250 L200 watt250 watttwo 250 watt
75 gal/300 L250 watt300 watttwo 300 watt

I would always recommend using 2 heaters for your aquarium which are equal to the total wattage required. So for example if you have a 100 litre aquarium and need to heat it from 18 degrees to 28 degrees (10 degree C increase) then the table recommends using a 100W heater. I would however use 2x 100W heater. Provided you are using thermostat integrated heaters (of which most are these days) then you will not use up any more power or electricity as they wont be on for as long to heat the water. This is simply a precautionary measure in case one of the heaters fails, the secondary heater would still be capable of heating to the correct temperature, giving you time to purchase a replacement second heater.

Fish Tank Heater Guide

This is purely a guide and should give a good rough estimate of what you would need for your fish tank to ensure the right temperature is maintained. It cannot hurt to have too much wattage of heat in the aquarium as they will simply turn off if the tank has reached the desired temperature.