So what exactly is the difference between a single and double pole thermostat? Both are types of line voltage thermostats, which typically control radiant, convection or resistance heaters. The difference is all about the off setting -- or a lack of one. Double pole stats have a true off setting. Single pole thermostats don't. That might not seem like too big of a deal to some folks, but there are some safety implications to consider.
What many people think is an off setting on the single pole thermostats, is actually a low setting. That means the heaters will turn on when the temperature dips below a certain temperature, which is usually around 45 degrees Fahrenheit. If a double pole stat is turned all the way counterclockwise, it is off and will not turn on, even in the case that a home dips below 45 degrees. This brings up an important thing for people to remember: avoid placing items directly on heaters or close to them. You should always mind heater clearance requirements, but this is particularly important with single pole thermostats because your heater will automatically kick on when the air temperature drops below a certain point. In some cases, folks go months without a heater turning on (especially in the summer) but when the first freeze hits the heaters will turn on without anyone thinking about it. If there are items placed on the baseboard, bad things could happen. The best way to make sure a heater is off, is to disconnect the power to the heater circuit at the main panel. Cadet Vice President of Engineering Craig Peterson says the easiest way to determine if you have a single or double pole thermostat is to turn off the power at the breaker that powers your heater and take the thermostat off the wall. If you see two wires coming out of it in the back you have a single pole. If there are four wires, you have a double pole. If you have more than four wires coming out of your thermostat, you most likely have a low voltage one, which would be used to control a central furnace, boiler, or something similar.