Reptile & Amphibian Forums

Hi, can anyone tell me what the major difference is between the two? And which is better?

Thanks,
Alex

A rheostat is essentially a light dimmer. It simply keeps a constant voltage on whatever the load is (probably a heat pad of some sort) to maintain a constant temperature. It will not take into account and adjust for changes in ambient temperature.

A thermostat reads the voltage at a prticular place, then turns the voltage to the load on and off to maintain the temperature within a range. Since it is measuring and adjusting for changes in temperature, it will compensate for changes in ambient temperature.

For instance, if you have adjusted a rheostat to maintain a temperature on a surface at 80 degrees f. and your ambient temperature is a 70 degrees f. when you set it up, as long as your ambient temp doesn't vary a lot, your temp will remain fairly constant. If your ambient temp rises to 80 degrees, then you will still be adding heat and your actual temp will rise somewhat above what you adjusted for.

If you are using a thermostat, it will turn off and turn on the heat source to maintain the temp you set, no matter the ambient temp. Of course, if the ambient temperature goes above what you have the thermostat set for, it will never turn the heat source on again until the temp goes below the stting again, but it cannot cool down the surface it is monitoring, it can simply stop applying additional heat.

Perfect explanation! Thanks! Thermostat it is for me.

Depending on your heating device, you may want both--some heating devices get very hot, very quickly. A thermostat would be constantly turning the device on and off, on and off, in such a case--a rheostat could be used to limit how hot the device becomes, so that it warms more slowly, and could put less strain on the device since it wouldn't but switched on and off so frequently.

If you are using heat tape or heat pads, you should have both. A thermostat to determine when the device is needed and a rheostat to regulate how warm it gets when it is on.

Or you could go with a proportional thermostat that does both things simultaneously (like a Helix or Big Apple system) although I still think having two separate units gives you more flexibility.
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Chris Harrison