Your Home Furnace Basics

Flame Lit – Part III – A limited micro-blog series of energy definitions and quick facts to help improve energy literacy

Your Home Furnace Basics

This piece is intended to help with general understanding of the basic process of your home furnace. Detailed descriptions of the many types of modern furnaces and their equipment can be found in the links.

In Canada, about half of us use furnaces to heat our homes. Almost 62% of the energy we use in our home is used to heat it! We can save energy, money, and greenhouse gas emissions if we pay attention to our furnaces!

How do they work?

“Forced Air” furnaces work by combusting a fuel, usually natural gas, and transferring the heat produced to air in our ducts which is used to heat our rooms. Here is the basic process.

The Spruce” has a great diagram and a detailed description of high efficiency furnaces.   

  1. An electronic ignitor or a pilot light remains on standby in your furnace
  2. You punch in your desired room temperature on your thermostat (let’s say 22 C)
  3. The thermostat sends a signal to your furnace and the natural gas valve opens letting fuel into the combustion chamber via the burners
  4. Gas and air are burned in the combustion chamber and heat is released
  5. The heat is transmitted to air in the ducts using a heat exchanger
  6. Forced Draft fans blow the hot air through the ducts, out your vents, and into your rooms
  7. Combustion waste gases (like CO/CO2/H2O), or exhaust, are routed out of your house through your flue or chimney system – usually through the help of an induced draft fan.
  8. When your home temperature reaches the setpoint (e.g. 22 C), the gas valve closes and your furnaces stops firing until you adjust the temperature again

Older style furnaces are about 80% efficient. That is, 80% of the fuel energy is used to heat your home. Most of the other 20% is lost as waste heat with the hot combustion gases that exit in your flue.

As of January 1, 2010, Canada required all new furnaces installed be high efficiency. The legislation calls for a minimum efficiency of 90% but some units operate at 98%!  

These furnaces use a second heat exchanger to capture the waste heat in the exhaust gases. They help save money and reduce emissions but also may require more maintenance.

Your furnace deserves attention to keep it running efficiently and safely. Most fuel suppliers offer annual inspections of your furnace (often free) and it is well worth the call.

Next: A Few Simple Tips to Save $ on Heating

Sources and more information can be found in these links:




Next: A Few Simple Tips to Save $ on Heating

Alisa Caswell has a degree in chemical engineering. She spent twenty years working in the oil and gas industry, including roles in business development, operations and energy conservation. You can follow her on Facebook, LinkedIn, or Twitter.

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