How to Determine the Heater Size for a 240 Gallon Fish Tank

Written by charles watson
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Aquarium heaters are important for larger tanks. They ensure that the temperature in your aquarium remains constant, and most tropical fish and corals will need the ambient water temperature to remain between 22.2 and 25.5 degrees C. Consistency is most important when heating your tank. Whatever temperature you choose, you want the tank to remain that temperature at all times. When choosing a heater for your larger tank, you will want to choose one that is durable and long lasting. It will be wise to invest in a higher-end heater that has a good track record. Most local fish stores will be able to recommend a quality heater to use in your tank.

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Things you need

  • Aquarium heater

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    Choosing a heater

  1. 1

    Follow this rule when choosing a heater for your 240-gallon fish tank: According to, you will need three to five watts of power per gallon of water you plan on heating. With that in mind, a 240-gallon aquarium will require a 50-watt heater. If you are unable to find a 50-watt heater, then you can purchase two 25-five watt heaters to add up to the wattage you need. If you plan on placing your heater in a high water flow area in a sump or in your wet/dry filter, you will need five to eight watts of power per gallon of water. Using this method you may need a 75-watt heater; again you can purchase two heaters to equal your total wattage. You should always make sure you need the heater before you go out and purchase it. Heaters are especially needed in the winter months in areas where the temperature falls below 12.8 degrees C.

  2. 2

    Research the different types of heaters that are available to you. Stay away from heaters that may come as part of a filter package. You will want to purchase a unit that stands alone and is easy to get to if problems arise. Most heaters can be fully submersed in water. Make sure that the heater you choose fits this description. You'll want to place your heater near an area with good water flow, but away from the main living space inside the tank. A sump is a great place to put your heater.

  3. 3

    Unplug your heater when you are doing water changes. New water introduced into your tank is usually colder than the water you are removing. If you leave your heater plugged in and on, the sudden temperature change could cause your heater to crack or explode. Following these tips and the formula in step one will ensure that you purchase the right type of heater for your aquarium. If you are unsure about the type of heater you need, consult your local fish store.

Tips and warnings

  • Install heaters in a space your fish don't frequent.
  • Follow all directions included with your heater.
  • Always unplug your heater when performing water changes.

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