Warm Air Heating System Maintenance

If your facility uses warm air heating, whether as a primary system or especially as a supplement to specific areas of the building, you run the risk of overlooking regular maintenance. The most common systems are:

  • Forced warm air (using a furnace)
  • Duct heaters or heat exchangers
  • Infrared heating
  • Space heaters

Warm air heating and ventilating systems will give satisfactory and dependable service, as long as they are properly maintained. While the amount of maintenance needed is minimal, it is vital for a trouble-free operation. The following items should be checked at the prescribed intervals.

Fans and Blowers

Fans and blowers need to be cleaned and properly lubricated. The fine dust that collects on the blades or vanes should be wiped off at least once a year. You should check the condition of the blades at the same time.

If any unusual sounds are heard, such as scraping or rubbing, investigate them immediately. Any obstructions to the free rotation of the blades can wreck the unit. Excessive vibration can also cause premature failure. Fans are normally balanced at the factory, but a balancing weight could fall off during installation or operation and cause excessive vibration.


Electric motors are rugged and simple machines that will give little or no trouble if given reasonable care. Make sure the bearings are properly lubricated. Do not allow dirt, dust, and oil to accumulate on the coils or windings. Selecting high efficiency electric motors will reduce energy consumption and provide significant savings over the life of the system.


Smaller capacity blowers and motors are usually equipped with either sealed ball bearings or sleeve type bearings. Sealed ball bearings require no lubrication; sleeve bearings need a few drops of oil approximately twice a year, or as recommended by the manufacturer.

Larger motors and blowers may be equipped either with ball bearings, which require regular greasing, or with oil-lubricated ball or sleeve bearings.

Always follow the manufacturer’s recommendations for the type of grease or oil to use in the bearings and the frequency of lubrication. Do not overlubricate motor bearings.

Fan Belt Drive

The blower of a warm air furnace is usually driven by an electric motor by means of a V-belt. The belt is fitted on pulleys mounted on the motor and blower shaft. The blower motor is often equipped with an adjustable pulley. By adjusting this pulley, the blower speed can be adjusted to change the volume of air moved through the heating system. Check the condition of the fan belts on a regular basis. Replace them when they show signs of fraying, cracking, and wear.

Pay attention to the alignment of the pulleys. To realign, loosen the motor hold-down bolts and slide the motor into the proper position. Don’t forget to retighten the bolts. Check the alignment with either a straight edge or a thin steel wire placed against the upper and lower side of the two pulleys. When the pulleys are in perfect alignment, the two rim edges of each pulley will touch the straight edge or wire at the same time. The grooves of the pulleys should be in a straight line and the motor and blower shaft should be parallel; otherwise the V-belt will fray and wear too quickly.

Check the tension of the V-belt. The V-belt should be snug in the pulley grooves but not overly tight. If the tension is too tight, it will put excessive force on the bearings and belt and will cause the equipment to fail much earlier than normal. If the belt is too slack, it will lose its grip and start to slip. A squealing sound from the blower compartment on startup is a good indication that the belt is not tight enough.

A good rule of thumb to determine the proper belt tension is that for each foot of distance between the pulley rims, the belt should have approximately 3/4 inches of movement when pushed vertically halfway between the pulleys.

If the blower or fan is driven by two or more belts, be sure to replace the belts as a set. Older belts may have stretched during normal service and may be somewhat longer than new belts. If a new belt is put on a pulley drive with an old belt, the new, tighter belt will take most of the load and wear too quickly.


Filters should be inspected monthly and cleaned or replaced at least twice a year, and more often if dust conditions are high. If the filters are not regularly cleaned, they will get clogged, which limits the airflow and results in insufficient heating and waste of fuel. Washable filters should be cleaned in accordance with the manufacturer’s recommendations. Disposable or throw-away filters should be replaced.


Be sure to observe the operation of the burner at regular intervals. Gas burners generally require no maintenance. The oil burner nozzle may require occasional cleaning to remove carbon deposits. If problems develop, it is best to retain the services of a qualified repair person.


Be sure to clean the thermostats on a regular basis to remove dust deposits. If problems develop, do not attempt to fix the adjustment. Instead, retain the services of a qualified repair person.


Most warm air furnaces are equipped with a humidifier. The operation and servicing of humidifiers should be in accordance with the manufacturer’s instructions. Be sure to review the instructions carefully—they can vary greatly based on the type of humidifier used.

Ducts and Outlets

Keep ducts as air-tight as possible. Leaks that may develop at the section joints are not as apparent as leaks in steam or hot water lines. These leaks can cause a lack of sufficient warm air supply to certain areas or result in a waste of heat. Be sure to find and repair any leaks as soon as possible. Keep outlets clean and unobstructed.