If you need to heat a space just enough to keep it from freezing this plug will turn on whatever is plugged into it when the temperature drops below 38 degrees F (3 C), and off again when it reaches 50 (10 C).
We found out the hard way this winter that our thermostatically controlled well hole heater gave out. This is really bad to discover in mid January with the temperature hovering near zero. But you never learn these things in the summer because, well...the temperature isn’t near zero. Sigh.
So, after several hundred dollars worth of repairs, we are now protecting all that expensive machinery with a $21 part.
It’s simple. Plug it in to a grounded 120V outlet, and then plug the heater into the little box. There is an indicator light that glows when the current is passing through the thermostat. The overall size is about 1 x 1 by 2.5 inches.
The only possible drawback I can see is that it only has one outlet.
Suggested uses are for electric heaters, heat lamps, heaters, heating cables, and engine heaters. There is a one-year limited warranty.
All I can tell you for sure at this point is that it works just fine. And I’m sure if it ever fails we’ll find out the hard way because we sure don’t spend our winter nights running down to open the well pit to make sure the little light is on.