Electrical switching of a heating element causes wear only if the heating element is temperature-cycling by a large amount. Consider a light bulb controlled by an ON/OFF controller. When the bulb is ON, the filament in the bulb may be at 200 deg. When the bulb is switched OFF, the filament may cool to the cage temp. This heating-cooling of the filament causes the wear. The more heating-cooling cycles with a large temperature delta you have, the faster the wear.



In heat pads/cable, the wear is less for a few reasons. One: we aren't talking about a brittle filament that is losing electrons to convert energy to light. And Two: The temperature of the filament in a heat pad is far less than in a light bulb.



Proportional controllers do not cause any undue wear on the heaters. In fact, since they maintain a relatively constant heat compared to ON/OFF controllers, proportionals are the best way to go. Doesn't matter if they are switching power to the heater all day long. The heater temp isn't changing much all day long. No worse than keeping the heater ON all day, or dimmed all day.



A dimmer acts alot like a proportional controller without the ability to maintain a setpoint as the load or background temp changes. A dimmer is not better or worse for the heater compared to a proportional controller.



And, a problem occurs with putting a dimmer in-line with an ON/OFF thermostat when you set the dimmer on a very low setting. The hysteresis in the dimmer trigger will cause the bulb or heater to not come back on once it goes off until you up the dimmer setting a little. This is a real pain. Only happens at low settings, but it happens.



Bottom line: For non-light-emitting heaters, proportional control is the best for temp control, for heater life, and for peace of mind that your temps will be at where you set them. For light bulbs, you can use a dimmer in line with an ON/OFF T-stat, but size the wattage of the bulb so you don't have to turn down the dimmer too low, this way avoiding that annoying hysteresis problem mentioned above.
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Mark G

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