Things You'll Need

Instructions

1

Turn off the furnace. If it's a gas furnace, shut off the gas supply.
2

Remove the access door on the front of the furnace. Remove the screws, or, depending on the type of furnace you have, slip the access door off its hooks.
3

Remove the furnace blower. The furnace blower is the object with fan blades on it. It is located behind the furnace access door. Make a note of which colored wires go to which connections. Disconnect the wires attached to the blower and unscrew the screws with a screwdriver. Slide the blower out of the furnace.
4

Remove the burner assembly. The burners contain the pilot light that lights the furnace. This is also located behind the access door. Usually, the burner is held in place with screws. Unscrew the burner assembly and lift it out.
5

Examine the heat exchanger for any signs of cracking, angling a dental mirror around the back side to check for cracks. The heat exchanger is typically located toward the back of the furnace, behind the blower and burner assembly. It is a metal wall that has tubing running up and down it.
6

Shine a flashlight into each of the heat exchanger cells. Look for light shining through a crack in the heat exchanger. This indicates a damaged heat exchanger.
7

Spray water on the exterior of the heat exchanger. Angle a mirror and a flashlight inside the heat exchanger. Check for wet spots that indicate a crack.
8

Insert a sulfur stick into each of the heat exchanger cells and ignite them. Walk around your home, sniffing for any indication of sulfur. If you smell sulfur, you have a bad heat exchanger.