Published: October 14, 2020 - By: - Categories: Equipment

Aquarium heaters are used to ensure the temperature is maintained at a steady and proper level for tropical fish. This equipment is extremely important for the fish since they are coldblooded and maintain their body temperature based on surrounding conditions. Wrong temperatures can stress the fish that leads to a significant decrease in their disease-resistant ability.

How does aquarium heaters work?

Most aquarium heaters are operated using a temperature control thermostat to sense ambient temperatures and automatically open or close the electrical circuit that heats the inside heating core. In this way, the heater maintains the aquarium water at the desired temperature with very little fluctuation.

How do I know if my aquarium heater is working?


Most heaters have an LED light indicator integrated into the unit that burns whenever the heater is actually operating.

Depending on the actual room temperature and how well the system is closed down (a strong reason to have a complete light canopy that prevents both evaporation and heat loss) the heater may run all the time or very little.

How many watts per gallon for aquarium heaters?

It is important to ensure you select the correct aquarium heater for the size of your tank. The rule of thumb we use is for 1 W per liter in a room with normal and stable room temperatures. This translates to about 3-4 watts per U.S. gallon.

A room kept between 70°F – 73°F will require the 1 Watt per liter or about 4 W per U.S. Gallon. A cooler room, such as a basement is going to require slightly higher (5 Watts per gallon) power.

This should enable the heater to overcome any wide variances for a standard aquarium level between 75°F – 79°F. This higher requirement is not required in all situations – only when the ambient room temperature is kept very cool, or the tank needs to be kept at a more elevated temperature.

How to install an aquarium heater?

Most aquarium heaters today are submersible and placed entirely under the water for their service life. When the aquarium is full, place the heater into position. It is important to remember that they do need time to acclimate to the ambient water temperature before plugging in.

Vertical or horizontal


One trick we have found is that the heaters seem to be more accurate if they are placed on a slight diagonal rather than strictly vertical. Why? I really have no idea. But straight up is less accurate than a ten-degree angle with the top off the center of the heater element.

Do not place a heater horizontally as well. This is the orientation where the heater is normally at its most inaccurate. This prohibition is usually shown on the packaging of heaters that are affected by this location.

Where to place the heater?

Do not place any standard aquarium heaters in a place where it is touched by anything. The heater tube must be fully exposed to the water around it. This prevents hotspots from building up and weakening the glass where a rock or ornament prevents the even distribution of heat off the glass. You should NOT bury the heater into the gravel as well.

Any wrong placements that disrupt the thermal conduction of the heater will cause the uneven distribution of heat and the tube will burst.

Aquarium heaters should be placed as directly in the filter flow as possible. This allows the heat to be pulled from the heater tube and evenly distributed around the tank as a whole. Proper current will prevent thermal layering from occurring. This is where inadequate currents are generated in the tank so some spots are left stagnant.

Ensure that you have no problem with the tank leakages and the water level is lowered to the point where the heater element may become exposed.

How to set an aquarium heater?


Most standard aquarium heaters often simply have a knob to adjust and the unit is set. If you have tropical fish, select one in the range from 75 to 80°F (24-27 °C) based on the tank species. 78°F is ideal for most tropical tanks.

After setting the desired temperature, place it in the filled aquarium for about 30 minutes before plugging it in. This gives the new heater and its thermostat ample time to adjust to the surrounding water temperature.

You can adjust the temperature setting once power is applied. There is no problem with this, but ensure NOT to take the heater out of the water when it is working. The sudden change between the warmed water and room temperature can destroy it.

Keep in mind that heaters deal with very high temperatures and are designed only to operate underwater. They should never have a hot element exposed to the air or they will break. This is the reason heater manufacturers will not warranty glass breakage.

Daily temperature verification with a thermometer

Zacro LCD Digital aquarium thermometerZacro LCD Digital aquarium thermometer

Make sure the temperature you are trying to get is the one you get. Never trust the heater calibration, you should always have a reliable independent thermometer to verify the level in the tank. Verify the reading once a day as part of your regular aquarium maintenance.

I always put my hand on the side of the tank when I verify the temperature. Over time I have come to know the temperature “by hand”. I usually know if there is something wrong before I even look at the thermometer.

How to safely remove a heater?

It doesn’t happen often, but sometimes aquarium heaters must be removed.

The heater elements on most standard heaters are ceramic, they are meant to retain the heat for an extended period of time. If the heater has been running, it should be unplugged for at least a half-hour before it is allowed to have the element area at the bottom of the heater exposed to the atmosphere.

The heat radiation characteristics are radically different between the water where it was designed to operate and the air. Even a warm heater element will most likely crack the glass.

The real problem is that it may not do it right away, it may just weaken the tube somewhat. I can’t tell you how often I have heard of a heater tube simply exploding in a tank “for no reason”.

The reason was that the warm element was exposed to the air and it weakened the tube. Over time and regular use, that tube strength deteriorates and finally “explodes” without any warning.

Placing a hot tube into the water is a great way to break the glass. It is not so difficult to do.

Treat a heater with great respect always give it ample time to cool down if it has been running. Don’t just plug it in to see if will heat up in your hand then put it back in a few minutes because the element feels cool.

Even if the heater was on for an extremely brief period under power for a few seconds, don’t play with fire. Give it a half hour or more after unplugging before it is suddenly exposed to water or air.

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