Most aquariums require some source of warmth to replicate the natural conditions in the artificial environment of the aquarium. Aquarium heaters are available for this purpose, and there are a few different types and brands to choose from. This article will discuss the most commonly used heaters, those which are removable and not buried in the substrate.

Most aquarium heaters use a bimetallic thermostat switch inside a glass tube where the heater element is, but at the opposite end. There is a compromise when you have this situation since there will be some heat making its way through to the sensing switch. But it works well enough to keep the tank temperature regulated within a few degrees, and the better ones are good to +/- 1 degree F.

One thing to remember is that you need to match the wattage of the heater to the aquarium size. If you have a “normal” room temperature of 70 degrees F, you can simply go by the manufacturer’s chart. Some charts will also show the number of degrees above ambient temperature (the temperature of the room the tank is in) also, like this chart:

http://freshaquarium.about.com/cs/tipsandtables/l/blheatersize.htm

This allows you to size the heater for colder rooms. A 150 watt heater may be fine for a 55 gallon tank in a room that is 70 degrees F year-round, but if you keep the room colder in the winter, for example, you might need two 200 watt heaters! Keep this in mind when choosing the wattage of your aquarium heater.

On the other side of the coin, you should realize that using a heater rated for a much larger tank may overheat the tank before it senses the temperature is too warm. It may not regulate within a degree or two of the desired temperature. This is not so much a concern with heaters that have an external controller and a separate thermal sensor. I have used a 350 watt heater with an external controller and separate temperature sensor and it regulated very close (within one degree) to the desired temperature—in a 10 gallon tank!!! This would not have been possible with an inline heater that has the thermostat in the same glass envelope as the heating element.

		Vertical Glass Envelope Heater with Top-mounted Controls The least expensive type is the one that has a temperature control dial on top and hooks over the edge of the tank. The control may or may not be calibrated. If it is not calibrated, you must put it in the tank and leave it alone for a set period of perhaps 20 minutes. Then turn the knob until the indicator light comes on and check your temperature on a thermometer. You turn it up or down in small increments until you reach the desired temperature for your tank water, then leave it alone. These work well but cannot be immersed in the water, so they are obtrusive. Most of these and the others discussed in this article have rubber suction cups to hold the heater tightly against the aquarium glass. While the vertically mounted heaters with the thermostat on top are less expensive, the most popular ones are the submersible inline ones.
		Inline Submersible Heater which can be mounted horizontally or vertically These can be immersed completely in the water and hidden behind plants, rocks, etc. Some have an accurate dial that allows you to pre-set the temperature, like the one shown above. Some brands are better at their calibration marks than others, but most will regulate to within 2 degrees either way of your set point. There is a variation on this, a composite material tube instead of the glass one, as in the Visi-therm Stealth models. You can’t see inside the tube since it is black, a plus for hiding it in the tank. The downside is that you won’t know when you have condensation you should be concerned about. But they are unbreakable, so if you have fish (or turtles) that like to ram the heater tube, this might be for you.
		A submersible heater with separate temperature sensor and external controller can be mounted either horizontally or vertically Another type of heater that is commonly used costs more, and the controller, heating element, and sensor are all separate. This is my favorite type of all of the aquarium heaters for a few reasons. Since the heating element is separate from the sensor, there is no knob that rotates that needs to be sealed from the water, and this lessens the chances of a leak past the seal around the moving temperature set dial. The one pictured below uses a titanium shell. Some of these have a digital temperature readout of the aquarium temperature. There are more expensive variations of this type where the controller actually hangs on the tank. This one is less expensive because the controller has the electrical plug on the back. If you have small animals that like to play with things, you might want to put some duct tape over the control knob to keep them from cooking or freezing your fish. Depending on where your plug is, you might find the cord on this model to be a bit on the short side, a problem remedied with a 3-wire grounded extension cord and a place to lay the controller close to the tank. Or, you could fashion some sort of hanger for the controller.