Your Forced Air Heating System


Certified Building Code Official


A majority of North American homes are heated with a forced-air furnace system which uses air as its heat transfer medium. These systems rely on ductwork, vents, and plenums as means of air distribution, separate from the actual heating and air conditioning systems. The return plenum carries the air from several large return grills (vents) to a central air handler for re-heating. The supply plenum directs air from the central unit to the rooms which the system is designed to heat. Regardless of type, all air handlers consist of an air filter, blower, heat exchanger/element/coil, and various controls. Like any other kind of central heating system, thermostats are used to control forced air heating systems.

The forced air furnace consists of two main areas; a burner compartment (firebox) and a heat exchanger. The heat exchanger is the medium used to transfer heat from the flame to the air, which moves through the house. Besides being the medium of heat transfer, the heat exchanger keeps the burned fuels separate from the air.

Heat Exchangers -- Forced Air Furnaces

The heat exchanger is the medium of heat transfer and separates the burned fuel from the air that moves through the house. Rust or cracking will allow CO gas to enter your home and usually requires furnace replacement.

When a heat exchanger cracks or fails, there are two points to consider involving air pressure. When cracks and rust, etc. are located at air pressure points, such as at turns and/or at the top of the heat exchanger (where the direction of the exhaust is not directed toward the flue), you may get combustion gases forced into the flow of the air in the plenum and ductwork.

Heating Defect Pictures

Most furnace water leaks originate from condensate lines and are easily fixed. Another source of water leaking into furnaces is the old style drum humidifiers. These are known for overflowing due to faulty floats which become stuck from calcium and mineral deposit build ups. Another source of water entry can be a poorly installed flue pipe which is allowing water to enter from exterior section of flue. Any sign of water or moisture presence in your furnace should be dealt with immediately by a trained furnace technician.

Furnace Heat Exchanger Crack

The general expected life span of a furnace is only ten years. Most forced air gas furnaces will last 20 years as long as the heat exchanger does not rust or crack. Water is the natural enemy of heat exchangers and the resulting rust will most likely require the purchase and installation of a new furnace.

Regular maintenance by a professional furnace technician can extend the life of your furnace and ensure it is operating at its optimum efficiency.

Using a pleated air filter with electrostatic strips are the minimum standard recommended by most furnace experts. The expanded surface area allows for greater air movement which does not restrict operation of fan unit and lower furnace efficiency.

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I. The inspector shall inspect:

A. The heating system and describe the energy source and heating method using normal operating controls.
B. And report as in need of repair electric furnaces which do not operate. 
C. And report if inspector deemed the furnace inaccessible.

II. The inspector is not required to:

A. Inspect or evaluate interiors of flues or chimneys, fire chambers, the heat exchanger, the humidifier or dehumidifier, the electronic air filter, solar heating systems or fuel tanks.
B. Inspect underground fuel tanks. 
C. Determine the uniformity, temperature, flow, balance, distribution, size, capacity, BTU, or supply adequacy of the heating system.
D. Light pilot flames.
E. Activate heating, heat pump systems, or other heating systems when ambient temperatures or other circumstances are not conducive to safe operation or may damage the equipment.
F. Operate electronic thermostats.
G. Evaluate fuel quality.