How to Calculate Amp Draw on Old Electric Baseboard Heaters


Electric baseboard heaters are perhaps one of the most efficient of the electric resistance heaters. One of the reasons these heaters are so efficient is the length of the heating element and the physical position of the unit. Baseboard heaters that are placed directly under exterior windows will aid in keeping the room warmer than when used alongside an interior wall. Older electric baseboard heaters are still efficient devices. The amp draw of any baseboard heater can be found by using a basic electrical formula.

Things You'll Need

  • Voltage of the baseboard heater
  • Baseboard heater’s total wattage output
  • Screwdriver (optional)
  • Find the amount of voltage that powers the baseboard heater. This can be done by opening up the main electrical panel. Locate the circuit breaker that controls the power to the baseboard heater. Identify the number of poles that is connected to the wires. If there is one switch for controlling the power, this is a single pole circuit breaker. The voltage is 120VAC. A double pole, double switch circuit breaker will be supplying 240VAC to the heater unit. The same holds true for fuses. A single fuse will supply the same as a single pole circuit breaker, 120VAC. A double fuse configuration also equals the voltage output of a double pole breaker, 240VAC.

  • Locate the total amount of wattage output for your particular baseboard heater. There is a small metal tag that has this information mounted on the device. Some units may have it displayed on the side of the unit. Other baseboard manufacturers may have the tag inside the end cover plates. Use the screwdriver to remove the end plates and read the tag. The tag may also display the voltage. It could read like the following: volts 240VAC, watts 4800 w.

  • Understand that a basic electrical formula exists for calculating wattage from volts times amperes (w = v X a). By performing a basic algebraic function, that formula can be manipulated to find amperage. The formula reads that amperage is equal to wattage divided by voltage (a = w/v).

  • Apply the amperage formula to find the amp draw on a baseboard heater that is supplied with 240VAC and will output 4800 watts. The formula will read: a = 4800 w/240VAC. The amp draw is equal to 20 amperes.

Tips & Warnings

  • Always remove the electrical power from any device whenever opening or servicing that particular unit.
  • Never remove the outer cover of the main panel box without first disconnecting all electrical power that supplies that distribution point. Failure to do so may cause a severe electrical shock.

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  • Photo Credit Hemera Technologies/ Images
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