How a Forced-Air Furnace Works


Your furnace is an essential part of what makes your home comfortable all year round. While most homes have some kind of forced-air furnace, most people don’t actually know how a furnace works.

This article will walk you through a few important pieces of information: how your home heating system works; how a gas furnace works; and what wear items to inspect and check periodically.

How Your Home Heating System Works

Your home HVAC (heating, ventilation, and air conditioning) system is generally composed of a few standard pieces of equipment:

  • The furnace – Most homes are heated using a forced-air furnace fuelled by natural gas, though it isn’t uncommon to find propane or electrically-heated furnaces
  • The thermostat – The thermostat controls the temperature and instructs the furnace when to turn on and off
  • The air conditioner – If your home has a central air conditioner, it will also be controlled by the thermostat
  • The humidifier – Most homes have a humidifier, which works alongside the other components of your HVAC system to keep your home’s air quality comfortable
  • Ducting – Not an “appliance”, but arguably the most important piece of the system, your ducting are what transport air throughout your home

In this article, we’re only going to look at the furnace and thermostat.

Setting & Maintaining a Comfortable Temperature

Your thermostat is usually mounted on a wall in the main floor of your home. It may be digital, with programmable options, or analog, where you simply set the desired temperature. Regardless of the type of thermostat you have, all thermostats serve a single function: to tell your furnace and air conditioner when to turn on and off.

When the temperature of your home deviates from what you have set at the thermostat, the thermostat will provide instructions for your furnace to activate. Shortly thereafter, warm air will be circulated throughout your home until the thermostat registers that the desired temperature has been reached.

Natural Gas as a Fuel For Your Furnace

A furnace has to have some kind of heat source in order to heat your home. Most homes in the tri-state area use natural gas, though you will also find propane and electric furnaces out there as well.

Natural gas is inexpensive and safe to use as a fuel source. So long as your furnace was properly installed and has been properly maintained, your natural gas furnace will provide many years of all-year comfort.

Furnace Pilot Light

Chances are that your furnace has a pilot light. The pilot light remains lit in order to ensure that natural gas does not leak into the home. If your furnace’s pilot light is out and cannot be relit (following the steps in your furnace owner’s manual), please call us and we will send a furnace repair technician to inspect your furnace.

Heat Exchanger

A natural gas furnace uses burners to warm up the heat exchanger in your furnace. The heat exchanger transfers heat from itself to the air that is flowing in and through it. It is more efficient to heat the air using a heat exchanger than it is to simply have air forced over the gas burners.

Maintenance Items to Ensure Proper Furnace Operation

Your furnace is generally “set and forget”, save for a few select wear items that should be checked and maintained when needed.

  • Furnace filter – Your furnace filter is inserted at a choke point between your cold air inlet and your furnace. It filters out particulates from the air, ensuring that nothing enters the furnace combustion chamber that could damage the furnace or catch fire.There are many types of furnace filters available. Most require replacement every 3-4 months. We include a brand new standard furnace filter in every annual furnace service/tune-up.
  • Ducts – Clean ducts ensure smooth, unrestricted airflow. It is important to have your ducts cleaned on a semi-regular basis. This ensures optimal airflow and improves indoor air quality.
  • Test safety mechanisms – Read your owner’s manual to learn about the safety mechanisms built into your furnace and how to test them. Periodically, test these safety devices to ensure they are functioning as intended. These can include emergency ignitions, gas shutoff valves, and other important safety features.
  • Preventative maintenance – We recommend that you have your furnace serviced by a professional on an annual basis. These inspections ensure that your furnace is performing at its most efficient; these inspections also provide insight into the health of your furnace, where any required furnace repairs are caught preemptively.
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866-792-7154
24/7 Emergency Availability
866-792-7154