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Different heater types explained

What is the difference between different types of heaters?

What is the difference between different types of heaters?
There are two main types of aquarium heaters on the market. Bi-metallic strip heaters (Elite/Radiant, AquaClear/Thermal Compact and Thermal Pre-Set) and electronic heaters (Fluval/Tronic).

All heaters have a ceramic heater core that uses electricity to generate heat. Similar to a heater element in the bottom of a kettle. The metal heater element is placed in a ceramic heater core to more evenly spread the heat generated.

The difference between the two types of heaters is mainly in the way that they switch themselves on and off. Bi-metallic strip heaters, have, as their name suggests, a strip of metal made from two metals, with different characteristics when exposed to heat, fused together. This strip completes a circuit to a set of points when the metal strip bends close enough to the contact.

When the heater is on, the heater element becomes hot and warms up the water in the tank. At the same time the air within the tube heats and warms the bimetallic strip as well. One of the metals in the strip expands faster than the other causing the strip to bend away from the contact point as it warms up. When it bends far enough away, the electrical circuit is interrupted and current to the heater core ceases. This turns the heater off. As the bimetallic strip starts to cool, as the temperature in the heater tube drops much quicker than the water temperature, the other metal in the strip contracts. This brings it back, once it is close, to the contact point. The circuit is re-established and the heater switches back on.

Hence the bi-metallic strip part of the heater is really a kind of switch.

Electronic heaters have an electronic circuit board that incorporates a solid state switch. The Fluval/Tronic design incorporates a thermo-sensor that is pressed firmly against the glass heater tube. Due to the thermodynamics of glass conduction, in effect it actually samples the water temperature outside the heater. It is this temperature reading that will indicate to the heater when it should switch on or off. The rise and fall of heater tube air temperature is not a variable, so the actual temperature control of the heater is more consistent and uniform, the heater turns off faster when the correct temperature is reached, and turns back on when a small drop in aquarium water temperature is detected.

Another advantage to the Thermo Sensor technology is that the heater will automatically shut off should the glass tube become overheated when it is exposed to air. Water removes heat from the glass surface as fast as it is delivered, but when the same tube is exposed to air, it cannot conduct the heat away as rapidly. When the glass heats up, the Thermo Sensor responds by shutting the heater off well before the glass can shatter.

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