Furnace room

The heating plant in a house is normally a furnace or a boiler. (See chapter 14.) In this chapter, the heating plant is called a furnace and the room in which it is located is called the furnace room.

In most homes, the furnace is located in the basement or lower level. It can be located in a large open area or confined in a relatively small room. In either case, the area around the furnace is considered a potential fire hazard. Consequently, there should not be any exposed wood framing in the ceiling or partition walls that are in close proximity to the heating plant. (See FIG. 11-11.) Exposed overhead floor joists or wall studs that are near the furnace should be covered with Type X fire-code plasterboard as a safety precaution. Sometimes I find that wood paneling has been installed around the furnace to make the area more attractive. However, it also makes the area more of a fire hazard, especially the portion of the wall around the chimney. (See FIG. 11-12.) If you find wood paneling near the furnace, you might consider covering it with fire-code plasterboard. There should be a minimum 2-inch clearance between the chimney and any wood framing or paneling. Note that the area around the furnace should not be used for storage. On many occasions I have seen combustible items actually stored against the furnace. Fortunately for the families involved, the items never ignited, but they could have!

Many heating systems have prefabricated chimneys that extend from the furnace room up through the interior portion of the structure, terminating above the roof. If the house has such a chimney, look at the joint between the chimney and the ceiling of the furnace room. If there are large openings, they represent a potential fire hazard and should be covered with a noncombustible material such as sheet metal. The open area around the chimney, if not properly blocked, can act as a flue and in the event of a fire in the furnace room, will draw the flames up to the attic.

Real Estate Home Inspection photographs of house defects  Real Estate Home Inspection photographs of house defects

While in the furnace room, also check for asbestos insulation around the furnace and heating pipes. (Asbestos as a health hazard is discussed in chapter 20.)


All fuel-burning heating systems must have adequate ventilation for proper operation. If the furnace is located in an unconfined space, the normal air infiltration into the area provides ventilation. However, when the furnace is located in a confined space such as a small room, inlet and outlet ventilation openings must be provided. The vent openings can lead directly to the outside or to a large unconfined area within the structure. The size of the openings depends on the total input (Btu/hour) rating of all the fuel-burning equipment in the enclosure. For most residential structures, an unobstructed inlet and outlet opening of 15 inches by 15 inches is sufficient.

If you would like to calculate the size of the vent openings needed, a safe formula to use is 1 square inch per 1,000 Btu/hour of input rating for both the inlet and outlet vents. The input rating will usually be found on a data plate mounted directly on the equipment. If the vent opening is covered by louvers, remember that metal louvers reduce the effective opening by about 25 percent and wood louvers by about 50 percent. An insect screen covering the louvers reduces the effective opening by another 25 percent.

Some homes have louvered entry doors to the furnace room, which provide the means for ventilation. Occasionally I find that for decorative reasons, the louvers have been covered over, blocking the effective ventilation opening. If the louvers have been covered, look for additional vent openings.

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