How Your Furnace Works

Guirguis Faltaos - 6/15/2023

When a home system’s thermostat is turned up, an electrical signal is sent to the heating equipment, where a valve or relay-switch starts the fuel-burning process. When the furnace heats up, another control turns on the blower fan, which circulates warm air throughout the house. In the case of a hot-water system, a pump circulates hot water into radiators located throughout the house.

Furnace Inspection and Filters

• Maintaining a Furnace
• Filter Information
• Furnace Inspection and Filters

It’s best to have professional HVAC technicians conduct inspections and adjustments on your furnace. There are some things that homeowners can do themselves, however — such as changing air filters on a regular basis. It’s a good idea to know some basics about the furnace used in your home.

Safety Alert: Always turn off the fuel supply and electrical power before doing any inspection or maintenance on your furnace. Determine where the fuel supply is located and know how to turn it off. Similarly, turn off the electrical switch that controls the power supply to the furnace. After you have finished inspecting your furnace, remember to turn the fuel line and electricity back on.

The best place to start on your furnace is with the filter. A dirty filter will cause excessive strain on your furnace, increase heating costs and reduce the life of your equipment. Make sure that your furnace filter has a cover over the slot, ensuring an efficient return-air system. Not having a cover poses a safety issue. Here are some general guidelines for maintenance on various types of filters:

• Examine inexpensive fiberglass filters once a month during the heating and cooling seasons.
• Pleated filters can last up to three months.
• Wash and rinse permanent filters monthly.
• Clean electronic air-cleaner filters every other month.

Furnace Maintenance

• Check to make sure the pilot light is burning. Some furnace units must be lit by hand if the pilot light goes out.
• Follow the instructions for relighting usually printed on access doors. If you have difficulty relighting the pilot light, call a qualified heating contractor for advice.
• Check the blower and vacuum out and dust or debris in and around the unit. Check or replace the filter every 30 days. A dirty air filter clogs the air flow and it can overwork the equipment.
• Lubricate the blower motor.
• Remove the flame shield and check the burner for corrosion. Check flames with the fan off and on to conform to proper operation.
• Check the flue for gaps or dents and make sure it is venting properly to the outdoors.
• Vacuum all the dust from the air registers around the house.
• Check motion and make sure they are clear of furniture rugs, drapes, etc. to let the air flow freely.

Filter Information

• Spun Fiberglass Filters are the least expensive, disposable filters. They don’t, however, adequately filter out finer particles.
• Pleated Disposable Filters are more costly but will provide four to eight times the filtering capability of the spun fiberglass filters.
• Washable Electrostatic Filters have a high initial cost but they are re-useable and offer much higher filtration rates.
• Electric Filters and Mass Media Filters offer superior filtration but they require modification to the ductwork for installation. But note that installing these types of filters is not a do-it-yourself project; they should be professionally installed.