I'm trying to figure out how to safely use a dimmer or router speed controller as an inexpensive heat level control for a (nichrome coil) resistance heater. I've read that you can use a dimmer switch as a heat control if you don't run it at more than 80 percent of its watt rating continuously. (I'm not sure what the issues are there... why would it be rated 25% higher than its continuous power handling ability?) I've also seen people using a router speed control as a heat control for small heaters. My understanding is that a router speed control is similar to a dimmer, turning the power off at a certain phase in each AC half-cycle to vary the average power. (But maybe chopping the falling edge of the half cycle rather than the rising edge, or something like that...?) Does it make sense to use a router speed control as an average voltage control for a simple resistive load? I would guess it's designed with an inductive load in mind, but basically a switched inductive load (brushed motor rather than inductive), and I don't know whether a straight resistive load would be a problem. BTW, the heaters in question do have a small startup surge, with the resistance going up 10 or 15 percent in the first second or so. (But less of a surge than for a light bulb; the filament of a light bulb burns much hotter.) I'm interested in using a router speed control, because Harbor Freight sells a 15-amp model that goes on sale every couple of months for $10-$15; a dimmer that could handle the same amps would be much more expensive. (The usual wall dimmers are 600- or 1000-watts, and even the 1000-watt models are several times as expensive as the 600-watt model, and more expensive than the router speed control.) I'd like to be able to run at least 6 amps @ 120V through whatever I use, maybe 12 amps. (Two 720 watt coils in parallel.) Would that work, and would it be safe?