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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
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Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I have a Mears M22-SP old thermostat. Inside the cover

Customer Question

Hi, I have a Mears M22-SP old thermostat. Inside the cover it says high voltage. 120-240 It is for electric baseboard heat. How do I know if it is 2 wire or 4 wire. How do I know if it is running on 120 or 240
Submitted: 2 years ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! There isn't much documentation on the Mears line voltage thermostats but the SP on the end indicates it's a single pole unit, so it should be a two wire unit. You will see if there are either two or four wires connected to the back of it if you remove the two screws holding on the wall but you should only find two. As far as whether the thermostat is 120 or 240, that is best found if you look at the breaker for your baseboard heater. If it's a 2 pole breaker like a dryer, a water heater or a range would be then it is 240 volts. If it is a single pole breaker like a lighting or outlet circuit would be then it's a 120 volt heater. It could be either voltage even though it's a single pole thermostat. Please reply back if I can answer further. Otherwise, please remember to rate positively before you leave. Bonuses are welcome and always very much appreciated! Thank you, Brian