How Often Should You Replace or Clean Your Furnace Filter? (Hint: Probably Sooner Than You Think)

Picture this: it’s February in Ontario. Your furnace is cranking away, working overtime to keep your toes from turning to icicles. But behind the scenes, one little neglected hero — your furnace filter — might be gasping for air under a thick layer of dust, pet hair, and who-knows-what. Not exactly a comforting thought.

If you’ve ever asked yourself, “how often should I change my furnace filter in Canada?”, you’re not alone. It’s one of the most common HVAC questions we get at LG Home Comfort — and for good reason. A clogged filter doesn’t just restrict airflow; it can drive up energy bills, strain your HVAC system, and tank your indoor air quality.

In this guide, we’ll break down everything you need to know about furnace filter replacement, from MERV ratings to seasonal schedules, and even what happens if you put one in backwards (yes, it matters).

Why Furnace Filter Replacement Matters

Your furnace filter does a lot more than keep the inside of your HVAC system tidy. It’s the front-line defense against all the airborne nasties that circulate through your home — dust, pollen, pet dander, mold spores, and more.

But when the filter gets too dirty to do its job, your system’s energy efficiency drops, your airflow becomes restricted, and your furnace has to work harder (and burn more gas or electricity) just to keep up. Over time, that stress can lead to breakdowns or even premature system failure.

If you want to improve HVAC efficiency, maintain clean air at home, and avoid surprise repair bills, changing your filter is a small but mighty step.

How Often to Change Furnace Filters: The General Rule

So, how often should you swap out your furnace filter?

Standard Replacement Guidelines:

These timelines depend on multiple factors, so don’t treat them as gospel. If you’re wondering how long a furnace filter lasts, it’s safer to check monthly — especially during heavy-use months like December through March.

Canadian Winters Call for Extra Attention

In Ontario’s harsh winters, your furnace runs more frequently, meaning your filter traps more particles in a shorter amount of time. If you’re wondering how often to change your furnace filter to avoid allergies, the answer might be as frequent as once per month, particularly if:

• You have pets
• You have known allergies or asthma
• You live in an urban area with poor outdoor air quality
• You live in an apartment or high-occupancy home

A good habit? Make a monthly HVAC check part of your winter routine. Just like salting the driveway or topping off the windshield washer fluid — it’s one more layer of seasonal protection.

What Affects Furnace Filter Schedule?

1. Pets in the Home

Hair, dander, and dirt infiltrating from the outside along with your furry friends? They all clog filters faster. If you’re wondering how often to change furnace filter with pets, monthly replacement is often your best bet.

2. Kids, Occupants & Indoor Activity

More people = more particles. High-occupancy homes, especially those with children, benefit from frequent filter changes to manage allergens and bacteria.

3. Poor Outdoor Air Quality

Living near traffic, construction, or wildfire-prone areas? Expect to change your filter more often due to higher indoor dust and debris levels.

4. Filter Type & Size

• Fiberglass filters: Cheap but need frequent changes (30 days or less)
• Pleated filters: More effective, can last 60–90 days
• HEPA filters: High-end, can last 6–12 months
• Reusable filters: Must be washed and fully dried every 30–60 days

Don’t forget to check the MERV rating for furnace filters. Higher-rated filters trap more pollutants — but also get clogged faster.

Signs You Need to Replace Your Furnace Filter

Not sure when it’s time? Here are your furnace filter’s cry-for-help signals:

• Higher heating bills
• Weaker airflow through vents
• Dust buildup around your home
• Allergy symptoms worsening
• Funny smell from vents
• System short-cycling or running constantly

Pro tip: Hold your filter up to a light. If light can’t pass through, it’s clogged.

Reusable vs. Disposable Furnace Filters

You might be tempted to go with a reusable furnace filter to cut costs. While they do last longer and reduce waste, they require consistent cleaning and careful drying to avoid mold buildup. If you’re wondering how frequently to clean reusable furnace filters, aim for every 30–45 days.

Disposable filters, especially pleated ones, are more convenient and often more effective at capturing allergens.

At LG Home Comfort, we typically recommend high-MERV disposable filters for Ontario homes with pets, children, or allergy sufferers.

DIY vs. Professional Maintenance

Changing a furnace filter is simple, but HVAC maintenance tips don’t stop there.

We recommend booking professional HVAC tune-ups in fall and spring. Our Ontario techs perform full inspections, clean your blower, check electrical components, and can catch problems early — like cracks in the heat exchanger — before they become costly repairs.

A clogged filter may just be the symptom. Think of professional servicing as an annual check-up for your home’s lungs.

Furnace Filter Costs in Canada

Costs vary depending on size, quality, and brand:

• Fiberglass filters: $5–$10
• Pleated polyester filters: $15–$40
• HEPA filters: $30–$100+
• Reusable electrostatic filters: $50–$100

Tip: Always check your furnace manual or ask an HVAC technician to recommend the right size and MERV rating for your system. Using the wrong filter can restrict airflow and damage your unit.

Location Matters: Ontario-Specific Advice

If you live in Toronto, Mississauga, Kitchener, or any part of Southern Ontario, your furnace sees long run-times through winter. Snow, urban smog, salt-laden air — they all impact your indoor air quality and filters.

Consider adding humidifiers or air purifiers to your HVAC setup to enhance comfort and extend your filter lifespan.

Looking for more Ontario HVAC maintenance tips? Check out our blogs on:

• Best Time to Book Furnace Maintenance in Ontario
• How to Improve Indoor Air Quality This Winter

Frequently Asked Questions

1. Is it bad to not change your furnace filter?
   Yes. A dirty filter restricts airflow, forces your furnace to overwork, and can lead to costly repairs or even system failure. It also reduces indoor air quality.
2. How often should you change your furnace filter in Ontario winters?
   At least every 1–2 months for standard filters, and monthly if you have pets, allergies, or live in high-smog areas.
3. Can a dirty filter affect heating?
   Absolutely. It can reduce heat output, cause uneven temperatures, and even make your furnace short-cycle or shut down entirely.
4. How much does a new furnace filter cost in Canada?
   Basic filters start at $5–$10, while higher-efficiency options range from $30 to over $100 depending on size and quality.
5. How do I know if my furnace filter is dirty?
   Look for visible dust buildup, grey coloring, or poor airflow. You can also hold it up to a light — if no light passes through, it’s time to replace.
6. Should I change my furnace filter monthly or quarterly?
   It depends on your home, filter type, and season. In high-use months or homes with pets, monthly changes are best. Otherwise, every 2–3 months is typical.