How do you know what the voltage of your electric baseboard heater is if there is no label on the heater?

Go to your power panel and look for two pole breakers. If there are any 20 amp two pole breakers there is a good chance that they are for the baseboard heaters. Switch this breaker off and turn your thermostat up. If the baseboard heaters do not come on and get hot then this is the supply for them. A two pole breaker is supplying 240 volts to the heaters. Most likely there will be more that one heater on the circuit. <><><>

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.