Placement of Aquarium Heaters

home aquarium in a modern home

The optimal place for a heater in your home aquarium is near the highest water flow, such as the filter outlet (or intake) or the stream of a powerhead. Water running immediately through the heater distributes hot water across the tank fast and evenly.

Water Heater Size and Location

For most small aquariums in a home that is not very cold, the size of the aquarium heater should be 5 watts per gallon capacity of water. So a 20-gallon aquarium should have a 100-watt heater.

If your tank is larger than 40 gallons, try installing two at opposite ends of the tank; instead of one 200-watt heater, use two 100-watt heaters. The temperature of your water will be more consistent throughout the tank, and if one of the fails, the tank will not be left absolutely cold.

Heat Distribution in a Home Aquarium

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

  • Conduction: Conduction is the typical spread of heat from hot areas to colder areas, seeking a state of thermal equilibrium. When water is warmed up, the water molecules gain kinetic energy and begin bouncing around more; this energy spreads throughout the water as heat. Water is a decent conductor of heat, but most of your heat transfer in a tank will come from convection and circulation.
  • Convection: Convection occurs when the water becomes less dense and rises to the top as it warms, creating convection currents. When your heater warms up the water around it, the water rises to the top and displaces cooler water, which is denser so it sinks lower.
  • Circulation: The main vehicle for heat transfer in your aquarium will be from the circulation of water by your filter pump. Ideally, your filter will mix the water thoroughly to prevent any hot or cold zones from persisting in the aquarium.

Heat Circulation

Place the aquarium heater in an area with a lot of water movement, but avoid drawing newly heated water into the biofilter, which might kill your beneficial bacteria. Instead, situate the heater near the filter outlet; the warm water from the heater will be forced into colder water by the circulation current.

Place the heater horizontally at the filter outflow, slightly above the gravel (assuming that it is a fully submersible heater). Putting an air stone under the filter intake will also lift denser chilly water from the aquarium's bottom up into the circulation stream and into the filter.

Heater Selection

It is usually preferable to have a completely submersible heater than a partially submerged heater. This allows the enthusiast greater positioning options for whichever heating location is required. Put an air stone under your heater if it can only be immersed halfway to assist suck the chilly water up to the heat source.

Because horizontally positioned submersible heaters may not survive as long, most heaters should be replaced once a year. Only the most expensive heaters are built to survive a long time; the older the heater, the greater the risk of failure. It might either cease operating fully or never switch off, cooking the fish! Thermostats control heaters, and cheap heaters have simple connections. It pays to invest in a higher-quality heater for the sake of your fish's safety.

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