Measure the distance from the baseboard heater mounting location to your breaker panel. These measurements will include the distance from the baseboard to the ceiling, across the attic to above the breaker panel, and down the wall to the panel. Add at least 10 feet to this measurement.
Cut a length of 10/2 nonmetallic electrical cable equal to your measurements. The cable consists of a 10-gauge black solid wire, a 10-gauge white solid wire and a bare copper ground wire.
Slide a stud finder over the mounting wall to locate the studs. Mark each stud location with masking tape.
Place the baseboard heater on the mounting wall, so the end of the heater with the thermostat is between two studs. Make sure the mounting holes on the baseboard heater line up with the studs.
Mark the thermostat end of the heater on the mounting wall. Move the heater from the wall and drill a 3/4-inch hole through the wall board behind the heater using a 3/4-inch wood drill bit and power drill.
Unbend a heavy-duty large paperclip. Push the paperclip through the ceiling, where the wall and the ceiling meet, above the hole you drilled in the mounting wall. Continue to push the paperclip through the wall board to ensure it penetrates the attic.
Go into the attic and find the location of the mounting wall. Use a flashlight to find the paperclip you pushed through the ceiling. Drill a 3/4-inch hole through the mounting wall’s top plate right next to the paperclip.
Feed a fish tape down through the hole in the top plate. Have an assistant watch for the end of the fish tape through the 3/4-inch hole you drilled along the bottom of the mounting wall. Grab the end of the fish tape with needle-nose pliers and pull it through the hole.
Bend one end of the 10/2 NM cable into a small hook. Place this hook into the loop on the end of the fish tape. Wrap electrical tape around the fish tape and the NM cable to secure the wire to the tape.
Reel the fish tape up through the wall and into the attic. This hides the NM behind the wallboard and pulls it into the attic. Cut the tape from the end of the fish tape to release the NM cable. Continue to pull the NM cable up through the wall until you only have two feet of NM protruding from the wall at the heater mounting location.
Look on the back of the baseboard heater to find a 3/4-inch circular knockout at the thermostat end. The knockout is covered with a metal disk. Position a screwdriver over the disk and strike the screwdriver with a hammer to knock the disk from the heater.
Insert the threads of a 3/4-inch clamp connector through the knockout from the back of the heater. Secure the connector with the locknut provided with the connector.
Feed the NM cable through the connector in the heater. Push the heater close to the wall. Tighten the two screws located on the clamp connector to keep the wire secured in the heater.
Line up the mounting holes on the heater with the wall studs. Drive the mounting screws, provided with the baseboard heater, through the mounting holes into the studs.
Remove the exterior casing on the NM cable with a cable ripper to free the three wires inside the cable. Cut the wires with wire cutters, leaving about 8 inches of wire protruding from the heater.
Strip 3/4 inch of insulation off the ends of the black and the white 10-gauge wires with wire strippers. Wrap a piece of black electrical tape around the white wire to indicate that the white wire is now a hot wire. A 240-volt circuit does not require a neutral wire to complete the circuit, and by marking the white wire as a hot wire, you do not have to add the expense of the extra wire.
Connect the black wire from the NM cable to one of the red wires attached to the baseboard heater thermostat by twisting a red wire connector onto the wires. Connect the white wire to the remaining red thermostat wire from the thermostat with another red connector.
Connect one of the black wires from the baseboard heater to one of the black wires on the baseboard heater thermostat with a red connector. Connect the two remaining black wires from the heater and thermostat together with another connector.
Twist a red wire connector onto the green and bare copper wires to connect the two final wires together. Push all the wires into the heater and attach the thermostat to the heater with the mounting screw provide with the heater.
Turn off the main breaker located at the top center of your breaker panel. This breaker is separated from the other breakers in the panel.
Remove the screws holding the cover on the breaker panel. Pull the cover off the panel exposing the wires connected to the current breaker in the panel.
Go into the attic and pull the NM cable across the attic to the wall plate above the breaker panel. There may already be several wires feeding down from the attic and into the panel box. Drill another 3/4-inch hole through the wall top plate above the panel if necessary.
Have your assistant feed the fish tape through one of the knockouts in the top of the panel box and into the attic. Attach the NM to the fish tape with electrical tape and pull the wire from the attic and into the panel box.
Insert the back of a 30-amp, 240-volt double-breaker into the slot along the edge of the breaker panel. Push the front of the breaker down onto the center bus bar until it snaps in place.
Cut the access wire from the new NM cable, leaving enough wire to feed around the inside perimeter to the back of the new breaker. Rip the exterior casing from the NM cable and strip the insulation from the wires.
Slide the black wire underneath one of the terminal screws in the rear of the new breaker. Wrap a piece of black electrical tape around the white wire and insert it underneath the remaining terminal screw in the breaker. Tighten both screws to hold the wires to the breaker.
Find the thin, silver bus bar along the inside perimeter of the panel box that has green and bare copper wires connected to it. Slide the bare copper wire from the new NM cable under an empty terminal screw, then tighten the screw to hold the wire in the ground bus bar.
Replace the cover onto the breaker panel. Turn the main breaker panel back on to power the breakers in the panel.