How it works
Thermostandard mathCurrent (amps) = heater watts ÷ circuit voltage. A thermostat is listed when its maker-stated maximum current at that voltage is at least the figure. Where the maker gives watts only, its rating is converted at the highest voltage it lists.
ExampleA 2,000 W heater on 240 V draws about 8.3 A; the same heater on 120 V would draw about 16.7 A. That's why baseboard heat is usually wired at 240 V, and why a thermostat's rating has to match the voltage you have.
PolesDouble-pole thermostats break both hot legs of a 240 V circuit and can switch the heater fully off; single-pole models break one leg only. The maker's instructions say which your heater needs.
SafetyLine voltage can kill. Switch the breaker off, confirm it's dead with a tester, and have a licensed electrician do any work you're unsure of. This checker doesn't size breakers or wire.
Questions shoppers ask
How many baseboard heaters can one thermostat control?
As many as its rating allows. Add up the heaters' watts and divide by the voltage; the result must be at or under the thermostat's maximum current.
Can I use a Nest or ecobee on baseboard heaters?
Not directly. Those are 24-volt thermostats. Use a line-voltage smart thermostat, or a relay the maker approves for that use.
Is 208 V the same as 240 V?
No. Some apartment buildings supply 208 V. Heaters and thermostats rated for 240 V often list 208 V too; check the rating plate.