Standard Aquarium Heaters

Aquarium heaters are used to ensure the temperature is maintained at a steady and proper level for tropical fish. The most common aquarium heaters are operated using a bi-metallic strip as the temperature control thermostat.

This style of heater control is used in many home heater systems as well.

Bi-Metallic thermostats operate with a strip of two different fused metals that expand an contract differently. This will make the strip move one way as it cools and the opposite way when it warms.

These strips are used to open and close the electrical circuit that heats the ceramic core.

The thermostat does not operate by sensing water temperature. The bi-metallic strip reacts to the air temperature in the actual heater tube - not he actual temperature of the aquarium water.

This can cause the heater to turn on and off quite a number of times as it heats water to the desired temperature. This design is the most basic design. Standard aquarium heaters sold in pet stores will often utilize this type of thermostat to control the amount of time the heater is "on".

Most heaters have a pilot light 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.

The only way to know when it is doing so is to monitor the pilot light, when the pilot light is on, the heater is heating the water.

A heater may, for instance, be sold as a 100 Watt heater. This size is normally for smaller aquariums. This is a standard aquarium heater size and will use 100 Watts of power per hour when it is actually heating the aquarium.

In many cases this is not the case. The heater only uses power when it is delivering electricity to the heater element. As the tank becomes heated the air in the heater tube will become warmer as well.

When the increase in the tube temperature is enough to bend the bi-metallic strip away from the electrical contacts; the heater will shut off. The pilot light also will turn off.

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 a normal and stable room temperature. The translates to about 3-4 watts per U.S. gallon.

A room kept between 70oF - 73oF 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 75oF - 79oF. 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.

Setting the heater

When installing standard aquarium heaters, it important to remember that they do need a time to acclimate to the ambient water temperature. When the aquarium is full, place the heater into position.

Non-submersible heaters must be clipped to the aquarium rim and protected from splashing to prevent water entering the open topped tube.

Submersible standard aquarium heaters are just that. If the unit is marked submersible, they can be placed entirely under the water.

Many electrical certifications are written to prevent a cord from being placed in the water, so many are etched with a maximum water line. Following this guideline will keep the heater from being fully submersed.

The fact is that the construction of the heater is such that it can be completely underwater for its entire service life.

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.

Heater Placement Warnings

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. The same rule applies to burying the heater into the gravel:

- Don't do it!

The thermal conduction of the heat is disrupted and the tube will burst from the uneven distribution of heat.

As mentioned above, the heater is often most accurate when set into the tank on a small angle. Total submersion or only inserting in to the water line do not seem to be a factor.

Do not take this to the extreme and place a heater horizontally. This is the orientation where the heater is normally at its most inaccurate. This prohibition is usually shown on the packaging of heaters tht are affected by this location.

Standard 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 and today's modern pump technology will usually prevent thermal layering from occurring. This is where inadequate currents are generated in the tank so some is left stagnant.

Make sure the pumps are thoroughly mixing the water and keep it moving at all times. Older aquarists occasionally had this problem when less powerful equipment, especially pumps and filters were the only thing available.

Inserting the heater in a tank

Heaters deal with very high temperature and are designed only to operate under water. They should never have a hot element exposed to the air. This is the reason heater manufacturers will not warranty glass breakage.

A heater should be placed in the aquarium for about 30 minutes before power is applied. This gives the new heater and its thermostat ample time to adjust to the surrounding water temperature.

Once power is applied, you can adjust the temperature setting.

Most standard aquarium heaters often simply have a knob to adjust and the unit is set. Make sure the temperature you are trying to get is the the one you get. Never trust the heater calibration, you should always have an 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.

Removing a heater

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

This is more dangerous when there is a problem with the tank and the water level is lowered to the point where the heater element may become exposed. 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 a 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.

Temperature limits of heaters

There are many features offered with heaters, one of the most common is that the unit and its available range is pre-set and calibrated in the factory.

The factory could be located anywhere in the world, Italy and China are some that come to mind. Depending on the weather - especially humidity - at the time of manufacture, the actual aquarium characteristics could be different in your location than the factory's laboratory

The setting may not be 100% accurate, but even it if is, you should always have a reliable thermometer to verify the aquarium temperature easily.

Experienced aquarists often check temperature "by hand".

Over time, if you place your hand on the tank whenever you check the level, you will get a feel for the standard temperature in your tank. You'll know immediately if there is any radical change in the temperature level of the aquarium with every touch, no matter what the heater is doing.

Standard aquarium heaters are set and calibrated for standard aquarium temperatures. The ratings for most heaters are for room temperature, about 69 F, and the water temperature somewhere between 74 F and 78 F.

There IS a correlation between the amount of heat radiated by an aquarium and the room temperature. The heater is designed to keep proper temperature within a ten degree band between heater setting and ambient room temperature.

Assuming the desired temperature is within this window, heaters will usually work as expected. If you try to go outside this band, often the heater will track the room temperature as it varies.

People who have discus in the basement and are trying to heat a large tank well above the 10 degree range are often disappointed.

Standard aquarium heaters do not get consistently up to 82 F - no mstter what the pre-set dial suggests. The simple fact is that the tank has so much surface area that the heat in the aquarium is radiating faster than the heater can deliver it.

In cases like this, if there are much larger standard aquarium heaters available, that may solve the problem. Otherwise it is better to add a second heater as a redundant back-up and to deliver heat to the tank when the other is going full.

Usually a couple of heaters, set a degree or so apart, will be able to get the temperature up to the high ranges needed for discus and angels and account for the excessive radiation from the aquarium.

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