Furnace Maintenance

Learn how to take care of your gas furnace and ensure it's operating properly.

The basics

Keeping your furnace well-maintained and working normally is essential your for peace of mind — and to protect you from unexpected costs. It’s easy to do and all here in this guide.

First, learn how your thermostat works and set it correctly for your home.

Then it’s all about airflow: replace the furnace filter often, keep interior vents clear, and look out for intake or exhaust blockages.

Finally, even the cleanest homes and furnaces need a professional touch. Regular duct cleaning every one or two years, and regular tune ups for older furnaces.

Refer to the furnace glossary if you need help identifying furnace parts or terms.

Thermostats and settings

Knowing how your thermostat works and how to set it will help you recognize furnace problems and control your heating costs. 

The thermostat measures the indoor air temperature and calls for heat from the furnace as needed to maintain the set temperature. It is connected directly to the furnace control board with low voltage wires.

How your thermostat works — When the thermostat senses the temperature is below the set point it closes the low voltage circuit, which tells the furnace there is a call for heat. Within a minute or two, the furnace should turn on. When your set temperature is reached the thermostat opens the circuit again, which tells the furnace to shut off. In both cases, you might hear a ‘click’ from the thermostat.

Setting a schedule — Programmable thermostats can be set to turn down the set temperature at night and while you are away. Compared to using a “hold” temperature, setting a schedule can drastically reduce your heating costs.

If your furnace is behaving oddly, and you haven’t changed your thermostat settings, it could be a sign of a problem. Contact us for furnace service or try our furnace troubleshooting guide.

Aside from defects in the thermostat, there are a few other causes for strange behaviour. 

If lights or electronics are placed nearby, the heat from the device can make the thermostat register a higher temperature than the surrounding space. This will cause the furnace to start up late and shut down early — making your home feel colder than usual.

A similar effect can occur if the thermostat is located in direct sunlight at certain times of day. Some newer “smart” thermostats have features to counteract this, but it’s better to keep all thermostats out of the sun, if possible.

Yes. Smart thermostats connect and operate like a normal thermostat, but also use microphones, motion sensors, and smartphone apps to detect when people are at home. They save energy by actively adjusting the schedule and set temperature to only provide heating when required.

Smart thermostats from Nest and Ecobee can connect to most furnaces to provide these features. They can also notify you of possible issues with your furnace (by monitoring the typical time to reach the set temperature).

Some new furnaces are paired with thermostats that provide smart features, maintenance reminders, and error code reporting.

Homes with multiple heating zones typically have multiple thermostats, each one paired with a specific furnace. All of the above still applies, and settings can be customized by zone.

Replacing the furnace filter

The furnace filter traps dust and debris, preventing it from entering your furnace and recirculating through your home and ducts. Regularly replacing the filter removes the trapped contaminants to keep your air clean your furnace operating normally.

You should always have a furnace filter installed, even in the Summer, and especially if you have A/C or a high-efficiency furnace. Air conditioners and high-efficiency furnaces have delicate heat exchangers that are easily blocked and damaged by dust and debris.

When to replace the furnace filter — Furnace filters need to be replaced every three months or less. Set a reminder for yourself. If you wait too long, the filter can become blocked — causing increased heating costs, excess wear on the furnace, and poor indoor air quality.

Furnace filter sizing — It depends on your furnace. The current filter is a good place to start, and the size might also be stamped on the filter rack. Typical sizes (in inches) are 16×20, 16×25, and 20×25. If in doubt, check with your furnace manual or manufacturer.

Types of furnace filters — There are two main types of filters: standard format (1-inch thick), and large format (4- to 6-inches thick). Basic fibreglass filters are only a few dollars each. High-end filters with increased filtration can cost $50 or more.

How to replace the furnace filter — Open the filter cover (if you have one) and remove the old filter from the rack. Slide in the new filter, taking care not to force it. Ensure the arrow on the filter points towards the furnace. Close the filter cover. That’s it!

Yes. Filter changes can keep ducts cleaner for longer, until your next professional furnace cleaning. The furnace filter catches dust and other particles before they enter the furnace. Replacing a dirty filter removes that trapped dust and debris from the system.

Yes. You can buy standard-format filters with increased micro-particle ratings and large-format filters with higher MERV ratings.

Keep in mind that “better” filters can reduce air flow significantly, which can put excess strain on your furnace blower motor and increase your heating bill. If in doubt, refer to your furnace manual or ask the manufacturer which types are supported.

For maximum protection from allergens, dust, and pollutants, consider upgrading to an air quality system

Yes. Check your humidifier vapor pad every time you replace your furnace filter (three months or less). Replace the vapor pad if it’s dirty, damaged, or more than two years old.

If you notice the following signs, it might be time to change the furnace filter:

  • unexpected increase in heating bills
  • new sickness or allergy symptoms
  • more dust in the air or collecting on countertops, floors, and furniture
  • vent airflow is weaker than normal
  • it takes longer to heat your home

Interior vents and cold air returns

Your furnace pushes air out into your home through the vents (usually on the floor or ceiling) and pulls air back through cold air returns (usually on the baseboards).  

These vents and returns are easy to maintain, but it’s important to keep them clear of any blockages. 

Don’t place furniture or rugs on top of your floor vents, or directly blocking your cold air returns. Don’t install extra filters inside of your vents — that’s what the furnace filter is for.

If you need to adjust the temperature in certain rooms or areas, it’s okay to partially or fully close a few vents. However, most of them should remain open and unobstructed.

If you block or close too many vents or returns, your furnace has to run longer and harder to heat your home. Obstructed airflow will increase your heating bill and put extra strain on important furnace components. To avoid extra costs or furnace failure, don’t block your vents!  

Exterior intake and exhaust vents

Unlike older models with metal chimneys, newer furnaces and hot water tanks have plastic exhaust and intake vents that exit from the side of your home. These vents can be blocked more easily, so it’s important to know how to keep them clear and what to do in case of a blockage.

The best way to prevent blockages is to visually inspect your outside furnace vents on a regular basis — especially during extreme cold or heavy snowfall. 

Bird and animal nests — Some birds and animals will build nests or seek shelter inside a vent. Most vents have a guard, but you should regularly inspect them for holes. From a safe distance, look inside to check for signs of uninvited guests. 

Ice and snow — In cold temperatures, warm and moist air exiting exhaust vents can quickly freeze, causing ice formations from the ground up. Check for ice build up regularly, and knock it down before it reaches the vent. When it snows, remember to shovel under the intake and exhaust vents so they don’t get blocked by deep snow.

If an exhaust or intake vent is blocked, the first sign could be unusual operation. Your furnace or hot water tank may sense the blockage and not start up at all, or operate intermittently.

First, clear any snow that has accumulated around or under the the vent(s). 

If there is an ice blockage inside an intake or exhaust vent, try using an electric hairdryer to melt the ice. Do not use physical force, which can crack or break the vent pipe.

When snow accumulates around or under the vents, ensure it is shovelled away promptly. If icicles form on a vent, gently knock them off. If ice builds up towards the vent from the ground up, knock it over or remove it with a snow shovel.

If a furnace or hot water tank vent is freezing often, it may be improperly installed or require replacement. Contact us to have it inspected by one of our certified furnace technicians.

Routine maintenance

Even the cleanest homes build up dust and debris in the furnace ductwork over time. Get a furnace and duct cleaning every year or two to keep your indoor air as clean as possible. 

If your furnace is more than 10 years old, routine furnace tune ups will keep it operating at maximum efficiency and identify problems — before they become failures or major repairs. Our furnace maintenance plans include an annual tune up, furnace filters, and priority service.

Finally, be prepared for the unexpected. If you ever need emergency furnace repairs, don’t hesitate to call Advanpro — 24 hours a day, 365 days a year.

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Furnace repairs should only be performed by a certified technician.

This website is for informational purposes only. Advanpro Ltd. is not liable for property damage, personal injury, or death caused directly or indirectly by actions taken as a result of the information provided here.