How to Calculate Electrical Loads for Baseboard Electric Heaters

Written by g.k. bayne
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Calculating the electrical loads for baseboard heating must be done prior to installation. The main electrical panel that distributes the power must be capable of providing that electricity. Baseboard heaters are typically powered by 240 VAC. Some smaller units may also use the lower voltage of 120 VAC. Regardless of the voltage, each heater must be calculated on an individual basis, and then the totals of each unit added together. This will ensure that the main panel will have adequate circuit breaker space and power for the heaters.

Skill level:
Moderately Challenging

Things you need

  • Baseboard heater electrical specifications
  • Pencil
  • Paper

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  1. 1

    Make a list that includes the electrical specifications of each baseboard heater. Many manufacturers will list the wattage and the voltage of each unit. From these two values the amperage must also be calculated to identify the size of wires needed to power the heater, along with the correct value of the fuse or circuit breaker.

  2. 2

    Here's how to calculate the amperage for a baseboard heater that lists the wattage at 2,500 watts and 240VAC. The basic electrical power formula has wattage equal to volts times amperage (w = v x a). Through algebraic manipulation of that formula, the amperage can be found by (a = w/v). In this case, the amperage is equal to 2,500 watts divided by 240 volts. The amperage for this unit is equal to 10.41 amperes.

  3. 3

    Find the amperage for the same baseboard heater at 2500 watts, but it is powered by 120VAC. Using the same amperage formula, you divide 2,500 watts by 120 volts. The amperage is doubled at 20.83 amperes. As the voltage is cut in half, the amperage then doubles to provide enough power to the baseboard heater.

  4. 4

    Find the full-load requirements for five individual baseboard heaters using the wattage and voltage ratings in Step 2 from above. Each baseboard heater must be wired to accommodate 10.41 amperes. Wiring these heaters safely is the top priority. When calculating the load of the heater, the electrical circuit must not be overrated. In fact a derating of 80 per cent for each circuit is used for each heater. In other words, increase the load value of each baseboard heater by 20 per cent for safety. The 10.41 amperes is now calculated at a 12.49 ampere load. To make it easier, raise this value to 12.5 amperes.

  5. 5

    Find the total load rating of the five baseboard heaters with the 80 per cent derating value. Multiply five times 12.5 amperes. The total load is equal to 62.5 amperes at 240 VAC. The main electrical panel must be capable of providing this amount of power to the heaters at all times.

Tips and warnings

  • Follow all local electrical code regulations when installing baseboard heaters. Some communities may have special rules concerning baseboard heaters and the installation.

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