Aquarium Heater Calculator: Find the Perfect Heater Size for Your Tank

Your aquarium ensures the survival of cold-blooded creatures, which depend on water temperature to regulate their body temperature. Hence, providing and maintaining the right temperature is crucial. Depending on your setup, you can choose to use one or multiple heaters. Heater capacity, or heating power, is shown by its wattage rating.

Types of Aquarium Heaters

You can decide on the type and number of aquarium heaters to use.

Hang-on-tank: These heaters attach to the tank's rear, typically with suction cups, a hook, or another fastening device. They are only partially submerged and are less efficient than other types of heaters. However, they provide adequate heating for smaller tanks. For larger tanks, it's advisable to use more than one hang-on heater on opposite sides of the aquarium.

Submersible: Submersible heaters are fully submerged in tank water and can be mounted horizontally or vertically at the back. They're often placed horizontally near the substrate and offer more consistent and efficient heating than hang-on heaters, especially in larger tanks.

Heating cable: This is placed under the gravel or substrate and is connected to a control unit, useful for freshwater-planted aquariums to eliminate dead spots. However, repairing or replacing the cable requires disturbing the substrate, making it a less ideal choice for saltwater reef systems.

Finding the Right Aquarium Heater Size

Sizing a tank heater depends on the tank's water volume, the room's average temperature, and the desired water temperature for the tank.

For heater wattage, the rule of thumb is 2.5 to 5 watts per gallon of water volume. More wattage may be needed based on the desired temperature increase. If using multiple heaters, their total capacity should match the required wattage.

To adjust for room temperature, subtract the room's average temperature from the target aquarium water temperature. The result is the required heating in degrees.

Using the aquarium heater size chart below, find your aquarium size in the left column. Move to the column showing the number of degrees the aquarium needs to be heated. If between levels, opt for the next larger size.

Example:

• Average room temperature: 68 degrees F
• Target water temperature: 77 degrees F
• Heating required: 9 degrees F (77 - 68 = 9)
• Tank size: 20 gallon
• Heater size needed: 50 watts

Tips for Using Aquarium Heaters

• In larger tanks, or when the room temperature is significantly below the desired water temperature, consider using two heaters. Install them at opposite ends of the aquarium for even heating.
• Using multiple hang-on or submersible heaters is advisable for even heat distribution and less strain on each unit. If one fails, the temperature won't drop too rapidly, allowing time to replace it. It's wise to keep a backup heater.
• The heater tube length is crucial because heat rises. Generally, it should match your aquarium's height.
• Check for heat sources and room temperature fluctuations around the aquarium. Your tank might be near a vent or intermittent heat sources causing temperature changes.
• Always unplug the heater when draining the tank to prevent overheating when it's not submerged.
• Some heaters have numbered thermostat settings for precise temperature control. Others have controls ranging from low to high without specific temperatures. The former is easier to use, but always verify the setting maintains the correct aquarium temperature.
• Place the heater near the filter's water outflow to disperse heated water throughout the aquarium.
• Use an aquarium thermometer to verify the heater maintains the correct temperature. Move the thermometer to various aquarium spots to ensure uniform temperature.