Electric baseboard heaters provide a form of radiant heat, which uses natural air convection (hot air rises, cold air drops) to circulate heat into a room. In some climates, baseboard heating can provide all the heat required by a home, but it is more common for baseboard heating to provide supplemental heat for spaces where the central HVAC system is insufficient to the task. For example, in a basement or attic room conversion, it can be hard to extend the central forced-air heating system to heat the space, and electric baseboard heaters offer an easy way to serve those areas.
Electric baseboard heaters can be powered by either a 120-volt or 240-volt circuit. Electricians generally install 240-volt heaters, since they use lower amperage and are more energy-efficient than 120-volt heaters. Adding a 240-volt baseboard heater usually requires a new 20- or 30-amp double-pole circuit breaker and new circuit wiring to supply one or more heater units. This is a dedicated circuit that serves only the heater(s).
Installation of a circuit and heater is an advanced home wiring project that is normally done by a licensed electrician or heating contractor. DIYers should have considerable wiring experience before attempting this project, since it involves running electrical cables and installing and connecting a new circuit breaker in the main service panel.
Choosing a Heater Size
Baseboard heaters come in many sizes to match the heating needs of the room. The rating or heating capacity of a baseboard heater is commonly measured in wattage, which is governed by the length of the heater. A common rule of thumb is to provide 10 watts of heat for every square foot of space in the room, though this may vary somewhat depending on the configuration of the room and details such as ceiling height, wall insulation, number of windows, and other factors.
Baseboard heaters typically come in standard lengths, from 24 inches to 96 inches. A 240-volt 24-inch heater generally is rated for about 350 watts (sufficient for a small bathroom), while a 96-inch heater is rated for 2,000 to 2,500 watts (sufficient for a 200- to 250-square-foot space). You can also meet heating needs with two or more heaters that combine to provide sufficient heating.
While wattage is commonly used as a measure of heating capacity, the actual output of a heater is measured in Btu (British thermal units). The Btu rating can be helpful when comparing electric heater size to other types of heaters or heating equipment.
Locating a Heater and Thermostat
Baseboard heaters commonly are located under or near windows to take advantage of natural convection currents in the room and to offset the heat loss through the glass. Building codes do not allow baseboard heaters to be installed beneath wall outlets, and they require a minimum of 1 inch of air space under the unit for the convective airflow to work properly. They also should have at least 12 inches of clearance from window coverings and furniture.
Thermostats for baseboard heaters can go anywhere in the room but tend to give the most accurate reading when located on an interior wall and away from other heat sources. They are typically mounted at the same height as wall switches. Some baseboard heaters have thermostat units built into the heaters and require no wall thermostat.
Equipment / Tools
- Drywall saw
- Cable fish tape (if needed)
- Drill and bits
- Wire strippers
- Stud finder
- Torpedo level
- Electrical wall box
- NM electrical cable
- Double-pole line-voltage thermostat
- 240-volt electric baseboard heater
- 1/2-inch cable clamp
- 1 1/2-inch drywall screws
- Wire connectors
- Black electrical tape
- 240-volt circuit breaker
Install a Wall Box for the Thermostat
Make a cutout for the line-voltage thermostat and install a wall box. On finished walls, a standard "old work" (retrofit) switch box works well. Cutting the hole for the box usually can be done with a simple drywall saw.
At the location for the baseboard heater, you will also need to make a hole in the wall where the electrical cable will extend out from the wall and into the heater's wire connection panel.
Run Cable for the Circuit
A 240-volt baseboard heater requires its own dedicated 20-amp or 30-amp 240-volt electrical circuit. A 20-amp circuit can safely provide 3,800 watts of power, while a 30-amp circuit is suitable for up to 5,700 watts. The standard circuit cable for 20-amp circuits is 12-gauge cable; 30-amp circuits need 10-gauge cable. The circuit cable typically is a two-wire cable with ground, where both the black and white wires serve as hot wires.
Run two lengths of NM cable—one from the main service panel to the thermostat location, and another cable from the thermostat to the baseboard heater location. At the heater location, no wall box is generally required, since the wire connection panel on the heater serves as an approved box.
Running cable through finished walls can be a tricky operation, requiring saws, a drill, and electrical cable fish tape.
Mount the Baseboard Heater
The basic steps of installing a baseboard heater unit are relatively standard:
Remove the knockout on the back of the heater's connector box and install a 1/2-inch cable clamp to the box. Feed the circuit cable through the cable clamp and into the wire connection panel on the baseboard heater, leaving 6 to 8 inches of extra cable extending beyond the clamp. Remove all but 1/2 inch of the cable sheathing inside the connection panel, then strip 1/2 inch of insulation from the end of each conducting wire in the cable. Tighten the cable clamp onto the cable.
Use a stud finder to locate walls studs behind the baseboard heater. Fasten the heater to at least two wall studs, using 1 1/2-inch drywall screws. Use a torpedo level to level the unit if it is a type that is not floor-mounted. (Note: If you have a floor-mounted unit, you may have to cut out the baseboard where the heater goes in to fit the unit against the wall.)
Make the Wire Connections at the Heater
Look in the connection box for the factory wiring connection on the unit's heating element. Following the manufacturer instructions, disconnect the wire connector (wire nut) that holds the connection together.
Connect one factory wire to a hot power wire from the 240-volt circuit cable, and connect the other factory wire to the second hot power wire from the circuit cable. Note that in a standard 240-volt circuit, both the black and white wire serve as hot wires, since there is no neutral wire in this kind of circuit. Mark the white wire with a band of black electrical tape to indicate that it is a hot wire.
Connect the bare copper grounding wire to the green grounding screw in the heater connection box. Install the connection panel cover.
Make the Wire Connections at the Thermostat
Strip about 3/4 inch of insulation from each conducting wire from both cables in the thermostat box. Following the thermostat manufacturer's directions, connect the wire leads marked "line" to the wires entering the box from the service panel. Connect the wire leads marked "load" to the wires running to the baseboard heater. The bare copper grounding wires in the box should be simply joined together with a wire connector. If the wall box is metal, it also should be grounded by means of a grounding pigtail wire.
Tuck the wires into the box, secure the thermostat to the box with mounting screws, and attach the cover plate.
Note: Connections can vary considerably from manufacturer to manufacturer, so make sure to read the thermostat directions when making these connections.
Connect the Circuit Breaker
The last step to finishing the installation is to connect and install the 240-volt circuit breaker in the main service panel. This involves first shutting off the main breaker and opening up the panel. Then, you connect the new circuit's ground wire to the panel's grounding bar, and connect the black and white circuit wires to the screw terminal connections on the circuit breaker, then snap the circuit breaker into an empty slot in the service panel. Finish by closing up the panel and turning on the main breaker.
Working in the main service panel is a risky operation if you are not experienced. You must turn off the main breaker before working in the panel, but even with the main breaker off, there are elements in the panel that carry deadly current at all times. Never work inside a panel if you are not familiar with all of its parts and how to avoid shock.
Test the Heater
Turn on the circuit breaker controlling the heater circuit, then test the heater by turning the thermostat up to a high temperature to make sure the heater produces heat and responds accurately to the thermostat settings. Then turn the thermostat off and make sure the heater shuts off.