10 Frequently Asked Questions About Furnaces

A person is kneeling and installing a folded air filter into a home HVAC unit, wearing a white shirt, jeans, and a watch.

Whether you are a brand new homeowner, a current renter, or have owned a home before, chances are you’ve had to deal with your furnace at least a couple of times in your life.

Furnaces are what keep you toasty during brutal and bone-chilling Canadian winters and knowing how your furnace operates, it’s components, as well as how to troubleshoot basic furnace problems, goes a long way in keeping your household operating smoothly.

Below are 10 frequently asked questions about furnaces, as a primer into one of the most important machines in any Canadian household.

1. How Does a Furnace Work?

Most furnaces come with 5 main components, including the thermostat, burners, the burner motor, the heat exchange, and the ducts, which all work in unison to heat and distribute air throughout your house to keep your home at the desired temperature.

Your thermostat not only measures the temperature of the air in your home but also sends a signal using a gauge to tell your furnace when to turn on or off. A thermostat typically uses buttons or a dial to adjust the temperature, and you can buy programmable and non-programmable thermostats.

Programmable thermostats can automatically adjust the temperature at various points during the day and night, whereas non-programmable thermostats must be adjusted manually to change the temperature.

When the signal is sent from the thermostat and received in the furnace, fuel is ignited, and the heating process begins. Once the burners are fully lit, they begin to increase the temperature of the heat exchange system. A blower then circulates air over this heat exchange system. When the air has been heated to the right temperature, the air is channelled into the ducts and distributed throughout your home, warming your living spaces.

2. What Types Of Furnaces Are There?

Furnaces are divided into 4 main types based on the type of fuel they require. These include:

  • Natural gas
  • Oil
  • Electric
  • Propane

Although they all have their own strengths and benefits, Albertans typically favour natural gas and electric furnaces due to our colder climates.

Natural Gas

Natural gas furnaces are incredibly economical. According to their AFUE (Annual Fuel Utilization Efficiency) number, natural gas furnaces are typically the most energy-efficient, routinely clocking in at between 90 – 98% efficiency (depending on model).

Gas is also competitively priced compared to other fuels, making natural gas furnaces the favourite choice for many Albertans.


Electric furnaces are some of the cheapest to purchase and are smaller, which makes them appropriate for smaller homes, or more budget-conscious homeowners. Electric furnaces work differently than the other furnaces, in that they do not use a burner, but instead rely on an electrical ignition to heat conductive coils.

Electric furnaces are popular in areas where there are no natural gas lines installed, including some rural communities.


Like natural gas furnaces, oil furnaces burn fuel (in this case oil) to heat up your home. Oil furnaces are typically less expensive than natural gas furnaces are, but they are also less efficient with an average AFUE number of 80 – 90% versus 90 – 98% found in natural gas furnaces.

These are more commonly found in colder climates, and are popular in the northeastern United States.


If the other types of furnaces are not suitable for your home, there are also propane furnaces, which operate similarly to the natural gas and oil furnaces. Since propane is easily stored, however, this can be a great option for those without access to oil or a natural gas line.

3. What Is A Furnace Filter?

The humble furnace filter plays a vital role in improving your air quality and is responsible for catching debris, allergens and dust that collects in the return duct. This helps protect your blower fan and stops potentially dusty air from being cycled through your home.

Furnace filters come in a variety of sizes that fit your specific furnace make and model, so make sure you know what dimensions are appropriate for whichever furnace you own.

4. How Often Should I Replace My Furnace Filter?

Furnace filters, no matter their size, can easily get clogged with dust and other debris fairly quickly, particularly if you are using your furnace regularly. If you are using disposable filters, this means they should be checked monthly and replaced every 3 months to help ensure your furnace isn’t working harder than it needs to be.

Washable filters, although permanent and are a one-time purchase item, still need to be removed and cleaned regularly. Washable filters should be cleaned and checked at the same frequency as their disposable counterparts.

5. What Is A MERV Rating?

MERV is short for Minimum Efficiency Reporting Value, a rating between 1-16, denoting how efficient a filter is at trapping unwanted particles. The higher the MERV rating, the more particles will get trapped within the filter. A filter with a MERV rating of 9, for example, will trap significantly more particles than, say, a filter with a MERV rating of 3.

Filters with MERVs between 8-13 are some of the most common filter ratings for the typical home.

6. What Should I Do If My Thermostat Doesn’t Work With My Furnace?

If your thermostat isn’t working there are typically 5 main culprits:

  • A loose wire connection.
  • The thermostat is dirty.
  • The thermostat’s batteries are dead.
  • You’ve blown a fuse.
  • The thermostat is old and has reached the end of its life cycle.

Though you may be able to fix the problem yourself, we always suggest reaching out to an experienced repair technician. This can help ensure that the job is done safely and correctly.

For safety reasons, start by removing the batteries or severing the thermostat’s connection to the fuse box before you open the thermostat cover. Adjust and replug wiring, or tighten screws if these are the causes of the malfunction.

Most thermostat issues are minor and can be fixed at home, but there are times where a professional needs to take a look or outright replace it.

7. What Should I Do If My Furnace Stops Working?

Though the most common furnace problems stem from the thermostat, that doesn’t mean that other things can’t go wrong. So what should you do if your thermostat is fine, but your furnace still won’t run?

As with your thermostat, we suggest contacting an expert for assistance. However, if you want to take the DIY route, please make sure your breaker is off before you begin.

Here are some reasons why your furnace may be hitting bumps along the road:

Your Filter Is Clogged

If your filter is clogged, chances are that your heat exchange system is overheating, which may cause your furnace to shut down as a safety precaution.

Your Safety Switch Is Engaged

Furnace doors have safety switches that turn on when the door to the furnace has been opened or removed. If your safety switch is engaged, the burner and fan are automatically disabled, meaning that your furnace will not turn on. Check to ensure your furnace door is securely closed then try restarting your furnace.

Dirty Burners

Clean burners typically emit a blue flame. If your flame is yellow or red, it may indicate that the burner needs to be cleaned.

8. What Should I Do If My Furnace Blows Cold Air?

Picture this: It’s the first frigid day in a long Albertan winter, and your furnace decides it’s going to start blowing cold air. What do you do?

Before you panic and book your one-way flight to Maui, here are a couple of troubleshooting options you can try before calling in the pros for help.

Fan Settings

Depending on your current fan settings, you may be accidentally telling your furnace to alternate between blowing hot air and blowing cold air. This means your furnace will blow air even if it hasn’t heated it first.

Switching your fan settings to auto helps ensure that the fan turns off when heating your home is not necessary.

Check The Pilot Light

If the pilot light is off, it means the problem either lies with the pilot light or the burners. If this happens, you should call an expert for a more thorough investigation into the problem.

9. Can I Do Furnace Maintenance Myself?

Regular furnace maintenance (such as changing and inspecting filters) should be a part of your regular household maintenance routine. You should be checking on your furnace at least once per month to ensure everything is running smoothly, and any small issues can be addressed before they become bigger issues.

Though you may be able to fix minor issues yourself, you should always call an expert for bigger jobs, or whenever you aren’t confident you can safely fix the problem yourself.

10. How Often Do I Need A Tune-Up?

A yearly furnace tune-up can help catch and address small problems before they become bigger, more expensive problems. Regular maintenance is also typically less expensive than large scale repairs, which also cause unnecessary stress. During your annual inspection and maintenance appointment, your furnace technician will be able to pinpoint potential problems and offer solutions to keep your furnace running smoothly.

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