How To Size, Layout And Install Electric Baseboard Heaters

If you are currently adding the electric baseboard heaters to the home and would like to know how to size and install them, you come to the right place. Here are some electric baseboard heater rules of thumb that will help you install it correctly.

You are permitted to wire multiple electric baseboard heaters together. However, you need to pay attention to the total wattage and not overload your circuit breaker. The total wattage will also determine the wire and circuit breaker size.

Calculating Heater Wattage

To determine the total size of wattage needed for a room, multiply the length by the width of the room. Once you have that number multiply it by 10.

WARNING: 240 volts is beyond what most DIYers can safely handle. If you plan to install 240-volt baseboard heaters, consider working with a professional to install the units and wiring.

So, let’s say you want to install electric baseboard heat in a bedroom which is 10 feet long x 12 feet wide. So, the minimum total wattage needed is 1200 [(10×12)x10=1200]. This would require either a 1 – 5 foot heater (1250 watts) or 2 – 3 foot heaters (1500 watts) at 240 volts. Electric baseboard heaters rated at 240 volts are approximately 250 watts per foot.

Determining if you need 1 or 2 depends upon the number of windows in the bedroom and furniture layout. You want to place the heater under a window because the heat will rise to clash with the cold from the window, causing natural convection and circulating the heat around the room.

You are NOT permitted to install the heater under a receptacle or in any area where combustible vapors, gases, liquids, or excessive lint or dust are present. You also need 12 inches of clearance above the heater and 6 inches of clearance on each side of the heater.

To determine the wire and circuit breaker sizes divide the total wattage by the voltage, which will give you the amperage. Let’s say you install the 2- 3 foot heaters, then 1500 watts divided by 240 volts = 6.25 amps.

U.S. Electrical Code Guidance on Electrical Load vs Wire Size for Electric Heaters

According to the National Electrical Code® (NEC®) section 424.3(A), “Branch circuits supplying two or more outlets for fixed electric space-heating equipment shall be rated 15, 20, 25, or 30 amperes.” So, you will need to use a 15 amp breaker which requires 14 AWG wire.

According to NEC®, section 424.3(B), “Fixed electric space heating equipment shall be considered a continuous load.” This means that you are permitted to fill the circuit breaker to 80 percent of the total load.

So, let’s say that you want to put an adjacent bedroom on this circuit as well. Let’s also say this adjacent bedroom is 10 feet wide by 12 feet long. If you wired the two bedrooms’ heaters together, then the total connected load is 12.5 amps. You are only permitted to fill a 15 amp breaker to 80 percent of the total load or 12 amps. So you need to increase the breaker size to 20 amps and increase the wire size to 12 AWG.

How to install a programmable thermostat for electric baseboard heat?

As for the thermostat, I recommend a wall-mounted thermostat over a unit mounted t-stat. If your budget allows, I also recommend a programmable thermostat.

Using the wall-mounted t-stat will heat the room evenly. Using a programmable thermostat will allow you to turn your settings up and down automatically.

So, you can turn the heat down to 62 degrees during the day while you are at work and set it to automatically adjust to 68 degrees just before you arrive home. This is also recommended to do while you are sleeping at night. This will save you money on your electric bill.

To wire the room, simply install a cable from the breaker box to the thermostat and from the thermostat to the heater(s). The cable coming from the breaker box will connect to the line side of the t-stat, and the cable going to the heater will connect to the load side of the t-stat.

All-electric baseboard heaters come with instructions on how to wire them.

When determining the size of electric baseboard heaters, it is always recommended to little oversize it. There is no loss of efficiency by heating with baseboard heaters that are larger than the minimum requirements. 

If you are installing standard electric baseboard heaters, then you may install the wires at either end of the unit. However, if you are using the softheat electric baseboard heaters, then you can only install the wires on the left end of the unit.

Worked in IT for 10 years, specialising in computer measurement, resource and performance management and complex problem solving. Changed careers to HVACr in 2015.

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