How to Install a Baseboard Heater

Baseboard heaters are a nice addition to an area of your home that is drafty or colder than the rest of the house. Before purchasing a baseboard heater, choose a heater size based on the square footage of the room to be heated, allowing approximately 10 watts per square foot of room area. The main purpose of baseboard heaters is to supply supplemental heat. It can be very costly to heat an entire house with electric baseboard heaters.

Baseboard heaters come in two varieties: 120-volt and 240-volt. Due to the higher voltage, 240-volt models operate at lower amperage and tend to be slightly more energy-efficient than 120-volt heaters. Both types mount the same way on the lower portion of an outside wall. These heaters can be placed under windows if the manufacturer's recommendations allow for placement near curtains and furniture. They should not be placed below outlets where cords will drape over the baseboard heater.

Breaker and Circuit Wiring

Wiring baseboard heaters is as simple as adding a 20-amp circuit. Simply run a 12-2 non-metallic sheathed cable from the electrical service panel to the location of the baseboard heater. Since baseboard heaters have a built-in junction box, you won't have to cut in a junction box to feed it. Installing the breaker and making the final connections at the service panel should be done by a licensed electrician.

For a 240-volt baseboard heater, the black and white circuit wires will connect to a double-pole 20-amp breaker. The white wire will get a piece of black or red tape wrapped around it near the breaker (and at the thermostat and heater connections). This signifies that it is a "hot" wire rather than a neutral wire. The circuit will not have a neutral wire. The bare-copper ground wire will connect to the ground buss on the panel.

In the case of a 120-volt baseboard heater, the black hot circuit wire will connect to a single-pole 20-amp breaker. The white circuit wire will connect to the neutral buss and the ground wire to the ground buss.

Thermostat Wiring

When wiring a baseboard heater with a separate thermostat, you must install a length of circuit cable from the thermostat box to the heater. The thermostat wiring connections vary for 240-volt and 120-volt circuits.

In the case of a 240-volt connection, the two hot wires from the breaker connect to the two wires on the "line" side of the thermostat. The two hot wires on the cable leading to the heater connect to the two "load" wires on the thermostat. Both white circuit wires should be labeled as "hot" with a band of black or red tape. The bare ground wires connect to the ground screw or ground wire on the thermostat, via a pigtail wire.

For 120-volt wiring, the black hot wire from the breaker connects to the "line" wire on the thermostat. The black hot wire leading to the heater connects to the "load" wire on the thermostat. The white neutral wires from both cables are joined together in the thermostat box; they do not connect to the thermostat. The bare ground wires connect to the ground screw or ground wire on the thermostat, via a pigtail wire.

Heater Wiring

The circuit wires from the thermostat connect to the heater according to the manufacturer's wiring diagram, and wiring configurations may vary. With 240-volt circuits, typically each of the hot circuit wires connects to one of the heater wires, and the ground wire connects to the ground screw or ground wire on the heater.

With 120-volt heaters, typically the black hot circuit wire connects to one of the heater wires, and the white neutral circuit wire connects to the other heater wire. The circuit ground wire connects to the ground screw or ground wire on the heater.