How To Size, Layout and Install Electric Baseboard Heaters
February 15, 2009
I am currently adding the electric baseboard heaters to my home and I would like to know if the units require there own separate breakers or if they can be wired in such as multiple units on one breaker or on with other electrical receptacles. I have been unable to find a wire diagram for this issue.
You are permitted to wire the units together. However, you need to pay attention to the total wattage and not overload your circuit. The total wattage will also determine the wire and circuit breaker size. To determine the total wattage needed for a room multiply the length by the width of the room. Once you have that number multiply it by 10.
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 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 clashing with the cold from the window causing a 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 clearance above the heater and 6 inches 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.
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 foot wide by 12 foot long. If you wired the 2 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.
As for the thermostat, I recommend a wall mounted t-stat 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 t-stat 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 recommend to do while you are sleeping. This will save you money on your electric bill.
To wire the room simply install a cable from the breaker box to the t-stat and from the t-stat 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.
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 in the left end of the unit.
Regarding 120 volt heaters, I do not recommend using these as they use twice as much current than a 240 volt heater.
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