Aquarium Heater Placement and Heat Distribution in a Home Aquarium

When it comes to aquarium heater placement in your home aquarium, the best location is near the maximum water flow, such as the outlet (or inlet) from the filter, or in the stream of a powerhead. Having water flowing directly past the heater is what quickly and evenly disperses heated water throughout the tank, ensuring it is always at the appropriate temperature for the species of fish in your aquarium.

Learn more about aquarium heater placement, as well as how to select the right heater for your tank and how to use it correctly.

Water Heater Size and Location

For most small aquariums in a home that isn't very cold, the aquarium heater should be sized at 5 watts per gallon. For instance, a 20-gallon aquarium requires a 100-watt heater.

For tanks over 40 gallons, consider using two heaters placed at opposite ends of the tank. Instead of one 200-watt heater, use two 100-watt heaters. This ensures more uniform water temperature throughout the tank, and if one heater fails, the tank will maintain some heat.

Heat Distribution in a Home Aquarium

There are three ways in which heat can be distributed throughout your tank:

• Conduction: Conduction involves heat spreading from hot areas to colder ones, seeking thermal equilibrium. When water warms up, its molecules gain kinetic energy, move faster, and spread this energy as heat. While water conducts heat reasonably well, most heat transfer in a tank occurs through convection and circulation.
• Convection: Convection occurs when water warms, becomes less dense, and rises, creating convection currents. Heated water rises and displaces cooler, denser water, causing it to sink.
• Circulation: The main method for heat transfer in your aquarium is water circulation by the filter pump. Ideally, the filter will thoroughly mix the water, preventing persistent hot or cold zones.

Heat Circulation

Place the aquarium heater where there is high water flow, but avoid drawing newly heated water directly into the biofilter, as it may overheat beneficial bacteria. Instead, place the heater near the filter outflow, so the warm water is carried along with the circulation current into cooler water.

Place the heater horizontally just above the gravel near the filter discharge, assuming it's a fully submersible heater. Adding an air stone under the filter intake will pull denser, cooler water from the bottom upward with rising bubbles toward the circulation stream and into the filter.

Heater Selection

It is always advisable to have a fully submersible heater rather than a partially submersible one. This offers greater placement flexibility to suit different heating needs. If your heater can only be partially submerged, place an air stone under it to help draw cool water up to the heat source.

Submersible heaters may not last as long if installed horizontally, so it's wise to replace most heaters annually. Only very high-priced heaters are designed to last many years. Older heaters have a higher risk of failure, either by stopping completely or malfunctioning and overheating the water. Heaters run on thermostats, and inexpensive ones have basic connections. Investing in a better quality heater ensures the safety of your fish.