Aquarium Heater Size Guide

When it comes to selecting the best aquarium heater size there is no “per gallon” rule that works in all cases. More often than not the size of your heater will be determined by the wattage and quality of your heater. This means the cheapest, biggest heater may not be the best aquarium heater. In fact it is often better to go for one of the better small, high quality aquarium heaters, such as the Eheim Jager.

Actions speak louder than words however. Therefore I have gone and created a list of tables to help you find the right aquarium heater size for your tank. This information has all be gathered from manufacturers, manuals, reviews and personal experience. This will help you make a much better choice than a “x watt per gallon” suggestion.

Additionally we must take into account our homes average temperature. A wind breaker doesn’t work too well during a snowstorm, so we can’t expect a heater to work just as effectively with huge differences in temperatures. For this I have done three ratings for homes at 68, 73, and 78 degrees Fahrenheit.

Aqueon Pro Heater
Room Temperature 50 Watts 100 Watts 150 Watts 200 Watts 250 Watts
Cold Room (68 F) 14 Gal 19.5 Gal 37 Gal 52.5 Gal 60 Gal
Normal Room (73 F) 17 Gal 25 Gal 46 Gal 64 Gal 75 Gal
Warm Room (78 F) 20 Gal 30 Gal 55 Gal 75 Gal 90 Gal
Fluval E Series
Room Temperature 50 Watts 100 Watts 200 Watts 300 Watts
Cold Room (68 F) 10 Gal 20 Gal 43.5 Gal 66.5 Gal
Normal Room (73 F) 12.5 Gal 25 Gal 55.5 Gal 83 Gal
Warm Room (78 F) 15 Gal 30 Gal 65 Gal 100 Gal
Finnex Titanium Tube
Room Temperature 50 Watts 100 Watts 150 Watts 200 Watts 300 Watts 500 Watts
Cold Room (68 F) 10 Gal 20 Gal 30 Gal 60 Gal 80 Gal 100 Gal
Normal Room (73 F) 15 Gal 25 Gal 45 Gal 70 Gal 90 Gal 110 Gal
Warm Room (78 F) 20 Gal 30 Gal 60 Gal 80 Gal 100 Gal 120 Gal
Hydor Theo
Room Temperature 25 Watts 50 Watts 100 Watts 150 Watts 200 Watts 300 Watts 400 Watts
Cold Room (68 F) 2 Gal 5 Gal 14 Gal 23 Gal 26 Gal 53 Gal 80 Gal
Normal Room (73 F) 4.5 Gal 9.5 Gal 20 Gal 30.5 Gal 39.5 Gal 66.5 Gal 92.5 Gal
Warm Room (78 F) 7 Gal 14 Gal 26 Gal 40 Gal 53 Gal 80 Gal 105 Gal
Eheim Jager

The Eheim earns a special note here. It has far above average heating strength thanks to its special laboratory glass, which you can read more about on the best aquarium heater page.

Room Temperature 25 Watts 50 Watts 75 Watts 100 Watts 125 Watts 150 Watts 200 Watts 250 Watts 300 Watts
Cold Room (68 F) 4 Gal 6.6 Gal 15.8 Gal 26.4 Gal 39.6 Gal 53 Gal 79 Gal 106 Gal 159 Gal
Normal Room (73 F) 5.5 Gal 11 Gal 21 Gal 32.5 Gal 46.5 Gal 66 Gal 92.5 Gal 128.5 Gal 210 Gal
Warm Room (78 F) 6.5 Gal 15.8 Gal 26.4 Gal 39.6 Gal 53 Gal 79 Gal 106 Gal 159 Gal 260 Gal
ViaAqua Quartz
Room Temperature 50 Watts 100 Watts 200 Watts 300 Watts
Cold Room (68 F) 8.5 Gal 16.5 Gal 33 Gal 53 Gal
Normal Room (73 F) 11 Gal 21 Gal 41.5 Gal 66.5 Gal
Warm Room (78 F) 13 Gal 25 Gal 50 Gal 80 Gal
Marineland Precision Heater
Room Temperature 50 Watts 75 Watts 100 Watts 150 Watts 200 Watts 250 Watts 300 Watts 400 Watts
Cold Room (68 F) 8 gal 13.5 gal 19.5 gal 26.5 gal 36.5 gal 46.5 gal 53 gal 83 gal
Normal Room (73 F) 10 gal 17 gal 25 gal 34 gal 45 gal 58 gal 66.5 gal 104 gal
Warm Room (78 F) 12 gal 20 gal 29 gal 40 gal 55 gal 70 gal 80 gal 125 gal
Aquatop GH
Room Temperature 50 Watts 75 Watts 100 Watts 150 Watts 200 Watts 250 Watts 300 Watts
Cold Room (68 F) 8.5 gal 13.5 gal 16.5 gal 26.5 gal 33 gal 43.5 gal 52.5 gal
Normal Room (73 F) 11 gal 17 gal 21 gal 34 gal 41.5 gal 55.5 gal 64 gal
Warm Room (78 F) 13 gal 20 gal 25 gal 40 gal 50 gal 65 gal 75 gal
Tetra HT
Room Temperature 50 Watts 100 Watts 150 Watts 200 Watts
Cold Room (68 F) 4 Gal 18 Gal 24.5 Gal 33 Gal
Normal Room (73 F) 7 Gal 24 Gal 37 Gal 44 Gal
Warm Room (78 F) 10 Gal 30 Gal 40 Gal 55 Gal
Zacro
Room Temperature 50 Watts 300 Watts
Cold Room (68 F) 10.5 Gal 66 Gal
Normal Room (73 F) 13 Gal 72.5 Gal
Warm Room (78 F) 16 Gal 99 Gal
Aquarium Heater Size Graphs

For those who hate tables but don’t mind looking over graphs I have converted the data just for you. A quick glance is all it takes to find the perfect aquarium heater size for your fish tank.


Keep these tips in mind when deciding what aquarium heater size you need:

  • Small aquariums can be heated much quicker and should avoid oversized heaters.
  • Large aquarium heaters may not work as well as two smaller heaters. This is highly dependent on water circulation. Either choose two smaller heaters or direct strong currents towards your heater for the best results.
  • Always keep a back up heater! Even if your back up is a cheaper model it can still save your fish while you get a longer lasting model.

I cannot stress enough that the wattage of your aquarium heater is not the only factor for sizes. Cheaper models such as the Tetra HT cannot heat anywhere near Eheim or the Fluval E series heater. Only go for cheap heaters as back ups.

2 thoughts on “Aquarium Heater Size Guide

  1. Mike kennedy

    I have converted a IBC tote into a 200 gallon fish tank, in a insulated un heated room. Looking to heat it . I live in central Vermont .

    Reply
    1. Joshua@themandaringarden Post author

      Hey Mike, This is an interesting one. What I would do really depends on a few things.

      How insulated is this tote? aquarium glass is surprisingly insulating due to how thick it is. Totes on the other hand can be built with insulation or built to transfer heat really well. As the room is unheated this would make a major difference. When dealing with heating we need to look at the lowest temperature you will have to deal with, which seems to be below 10 degrees. I doubt the room is hitting that low of a temperature but if it is you would need some serious power. even 300 watt heaters are only able to heat a 100 gallon tank 15 degrees in a 70 degree room.

      Assuming you have not gotten any fish yet I would get two 300 watt heaters and put them on the opposite sides of the tank, staggering the heat by 2 degrees. This would mean one is set to 74 and one at 76. This lets the 74 shut off when not needed but turn on when the 76 needs help. Additionally it helps keep the water from heating too quickly when it is already warm outside and 2 heaters are not needed.

      With two heaters installed check on the temp a couple times throughout the day, especially at night when it gets even colder.

      If the rooms insulation keeps the temperature more consistent, then heating would not be as big of an issue. Still I would do at least two 300 watt heaters, as the value of the fish you would put in a 200 gallon tank would out weigh the cost of a second heater. Worst case you have a back up heater if one dies.

      Reply

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