FREQUENTLY ASKED QUESTIONS

What is the primary purpose of an air filter?

The primary purpose of an air filter is to remove contaminants such as dust, pollen, mold spores, and other airborne particles from the air passing through it. This helps improve indoor air quality and protect HVAC system components from dust buildup.

How often should I change my air filter?

The frequency of air filter replacement depends on several factors, such as filter type, indoor air quality, household size, and whether you have pets. In general, it is recommended to replace standard 1-inch filters every 1 to 3 months. High-efficiency filters may last longer, up to 6 to 12 months.

Are high-efficiency air filters worth it?

High-efficiency pleated filters, such as MERV 11 and MERV 13 models, capture significantly more airborne particles than standard MERV 8 filters. They are worth it if you or your family members suffer from allergies, asthma, or respiratory issues. For most Canadian homes, MERV 11 provides the best balance of performance and airflow without straining your HVAC system. MERV 13 provides even better protection but should only be used if your furnace manufacturer's manual permits it.

Can a dirty air filter affect my HVAC system's performance?

Yes, a dirty or clogged air filter can reduce airflow, forcing the HVAC system to work harder. This can lead to reduced efficiency, higher energy bills, and potential damage to the system over time.

What's the difference between MERV and HEPA filters?

MERV (Minimum Efficiency Reporting Value) is a rating system for air filters that ranges from 1 to 20. Higher MERV ratings indicate better filtration. HEPA (High-Efficiency Particulate Air) filters are a specific type of high-efficiency filter that can capture at least 99.97% of particles as small as 0.3 microns.

Do air filters help with odors?

Some air filters are designed to help with odors by incorporating activated carbon layers that absorb volatile organic compounds (VOCs) and other odor-causing particles. Standard particulate filters generally won't address odors.

How do I choose the right air filter for my home?

A: To choose the right air filter, consider factors such as the size of the filter required by your HVAC system, desired MERV rating, any specific allergies or health concerns, and whether odor control is important. Also, ensure that the filter won't overly restrict airflow for your HVAC system.

What MERV rating do I need for my home in Canada?

For most Canadian homes, MERV 11 is the best all-around choice. It captures fine dust, pet dander, mould spores, pollen, and smoke particles up to 65% efficiently, without restricting airflow in standard residential HVAC systems. Choose MERV 8 if you have no pets and no allergy sufferers and want the most economical option. Choose MERV 13 if someone in your household has asthma, severe allergies, or if you live in wildfire-prone regions of Alberta or British Columbia where PM2.5 smoke exposure is a seasonal concern. Avoid MERV ratings above 13 for standard residential furnaces — the increased airflow resistance can strain blower motors not designed for high-efficiency media.

What is the difference between MERV 8, MERV 11, and MERV 13?

MERV 8 (Economy) filters capture up to 35% of particles 10 microns and larger — effective for dust, lint, pollen, and pet hair. MERV 11 (Superior) captures up to 65% of particles 1 micron and larger — adding fine pet dander, mould spores, and smoke residue. MERV 13 (Optimal) captures up to 90% of particles 0.3 microns and larger — including airborne bacteria, fine PM2.5 particles, and wildfire smoke. The right choice depends on your household: no pets or allergies → MERV 8; pets or mild allergies → MERV 11; asthma, severe allergies, or wildfire smoke exposure → MERV 13. United Filter manufactures all three ratings in every standard size, made in Ontario, Canada.

Will a higher MERV filter damage my furnace?

It can, if your furnace isn't designed for it. Higher MERV filters are denser and create more resistance to airflow. Older or lower-powered furnaces with standard blower motors may struggle to pull air through a MERV 13 filter, causing reduced airflow, heat exchanger overheating, or blower motor failure over time. Always check your furnace manufacturer's manual for the maximum rated MERV before upgrading. If your manual specifies MERV 8 or MERV 11 as the maximum, follow that guidance. If you're unsure, MERV 11 is the safe choice for virtually all residential Canadian HVAC systems built in the last 20 years.

What furnace filter is best for wildfire smoke in Canada?

MERV 13 is the minimum effective rating for wildfire smoke. Wildfire smoke contains fine PM2.5 particles (0.4–0.7 microns in diameter) that pass through MERV 8 and MERV 11 filters without being captured. MERV 13 captures up to 90% of these fine particles. During active wildfire smoke events — common across British Columbia and Alberta from June through September and increasingly in northern Ontario — switch to MERV 13 and inspect your filter every 7 days, replacing it when the filter face turns visibly grey. Smoke-season filters can load in as little as 2–3 weeks instead of the usual 60–90 days.

What is the difference between MERV, MPR, and FPR ratings?

MERV (Minimum Efficiency Reporting Value) is the ASHRAE industry standard used by United Filter and most Canadian manufacturers. MPR (Micro-Particle Performance Rating) is a proprietary scale used exclusively by 3M/Filtrete. FPR (Filter Performance Rating) is a proprietary scale used by The Home Depot. They are not interchangeable but can be roughly cross-referenced: MERV 8 ≈ MPR 600 ≈ FPR 5; MERV 11 ≈ MPR 1500–1900 ≈ FPR 7; MERV 13 ≈ MPR 2200+ ≈ FPR 10. When comparing filters from different brands or retailers, always use the MERV rating as the objective benchmark — it is the only independent, standardized measure.

Is a furnace filter the same as an AC filter?

Yes — in virtually all Canadian homes with central heating and air conditioning, the furnace filter and the AC filter are the same physical filter. Your home's HVAC system uses the same air filter for both heating and cooling. Whether you're running the furnace in winter or the air conditioner in summer, the same blower motor circulates the air, and the same filter cleans it. You do not need to buy a separate filter for summer. The one filter does the work year-round. This is why it's important to check and replace the filter regularly in all seasons, not only during heating months.

Can I use a washable or reusable furnace filter in Canada?

You can, but there are important trade-offs. Washable filters have lower MERV ratings (typically MERV 1–4) and capture far fewer particles than pleated disposable filters. They require thorough rinsing and must dry completely before reinstallation — installing a damp washable filter promotes mould growth in your ductwork. In Canada's cold winters, drying time can be a practical problem. For households with allergy sufferers, asthma, or pets, the filtration trade-off is significant. Standard disposable furnace filters are the most practical choice for most Canadian homes — they don't need to be cleaned, and they maintain consistent filtration efficiency right up until they're replaced.

What filter do I need for a geothermal heat pump system?

Geothermal heat pump systems use pleated furnace filters in the same MERV 8, 11, and 13 ratings as standard furnaces — but they require oversized filter dimensions because geothermal cabinets have larger housings than conventional furnaces. Common geothermal sizes include 28×30×1, 28×34×1, 30×30×1, 30×32×1, 30×32×2, 30×36×1, and 30×36×2. Geothermal variable-speed blowers run longer at lower RPMs, meaning more total air volume passes through the filter — replace geothermal filters every 3–6 months instead of the 1–3 month schedule for standard 1-inch filters. United Filter stocks all major geothermal sizes with free delivery across Canada.

How do I find the right size furnace filter?

The simplest method: look at the side edge of your current filter — the size is printed directly on the frame in the format Length × Width × Depth (e.g., 16 × 25 × 1). This is the nominal size and is what you order. If the filter is missing or unreadable, measure your furnace filter slot with a tape measure, rounding each dimension up to the nearest inch. The most common furnace filter sizes in Canada are 16×25×1, 20×20×1, 20×25×1, and 16×20×1 for 1-inch systems, and 16×25×4 and 20×25×4 for 4-inch deep-media systems. If your dimensions don't match a standard size, United Filter manufactures custom-size filters to any dimension to the nearest ⅛ inch.

What is the difference between nominal size and actual size?

Nominal size is the rounded number printed on the filter packaging (e.g., 16×25×1). Actual size is the true physical dimension, which is typically ½ inch smaller on each face and ¼ inch shallower in depth (e.g., 15½×24½×¾). If your filter is measuring at an actual size of 15½ × 24½ × ¾, what you need to order is a furnace filter labelled 16×25×1, which is its nominal size. Always order by nominal size — the filter is designed to fit the slot labelled with that nominal dimension. Never measure an empty slot and order that exact measurement; always refer to the size printed on your existing filter frame.

What happens if I use the wrong size furnace filter?

A filter that's too small leaves gaps around the frame where unfiltered air bypasses the media entirely — dust, allergens, and debris flow directly into your ductwork and HVAC components. A clogged or incorrectly sized furnace filter can lead to higher energy bills, reduced airflow, and even system breakdowns. When airflow is restricted, your furnace's heat exchanger can overheat and your blower motor can fail prematurely. A filter that's too large won't fit the slot and can't be forced in without damaging the frame. The correct filter should slide in firmly with no visible gaps around the edges.

Are two "16×25×5" filters always the same size?

No — this is one of the most common purchasing mistakes for 5-inch deep-media filters. Different OEM manufacturers (Honeywell, Lennox, Carrier, Air Bear) define their own actual dimensions for what they label a "16×25×5" filter. The actual depth can be 4⅜", 4⅞", or 5¼" depending on the brand and housing model. Even a ¼-inch difference in actual depth will prevent the filter from seating correctly in the housing. Always check the actual dimensions printed on your existing filter before ordering a 5-inch replacement. United Filter stocks 16×25×5 filters in all three actual depth variants to match specific OEM housings.

How do I measure my furnace filter if the old one is missing?

Turn off your furnace. Open the filter access panel and measure the filter slot opening — length, width, and depth — with a tape measure to the nearest ⅛ inch. These are your actual dimensions. Round each measurement up to the nearest inch to get your nominal size (e.g., an opening measuring 15½ × 24½ × ¾ = nominal 16×25×1). If the measurement falls between standard sizes and doesn't round cleanly to a common nominal size, you likely need a custom-size filter. United Filter manufactures custom filters to any dimension — call (905) 403-0160 or order online.

Can I use a 1-inch filter in a slot designed for a 4-inch filter?

No. A 1-inch filter placed in a 4-inch slot leaves a 3-inch gap around the filter frame, allowing almost all air to bypass the media unfiltered. It provides virtually no filtration protection. Your HVAC system is also calibrated for the specific airflow resistance of the correct depth filter — using an under-sized filter disrupts this balance and causes the system to run inefficiently. Always use a filter that matches the depth dimension of your filter housing exactly.

Does United Filter offer custom size furnace filters?

Yes. United Filter manufactures custom pleated furnace filters to any dimension to the nearest ⅛ inch, available in MERV 8, MERV 11, and MERV 13. Custom filters are built at our Mississauga, Ontario facility using the same synthetic pleated media as our standard line. They are ideal for non-standard HVAC openings common in older Canadian homes, commercial conversions, or systems with unusual slot dimensions. To order, measure your filter slot (length × width × depth), round each dimension to the nearest ⅛ inch, and visit unitedfilter.com/pages/custom-size-furnace-filters or call (905) 403-0160.

How often should I change my furnace filter in Canada?

The general rule for Canadian homes is every 1 to 3 months, but the right frequency depends on filter thickness, MERV rating, household size, whether you have pets, and your local air quality. Specific guidelines by filter type: 1-inch filters (MERV 8) — every 30–60 days in average use; 1-inch filters (MERV 11 or 13) — every 60–90 days; 4-inch and 5-inch deep-media filters — every 6–12 months; geothermal filters — every 3–6 months. During wildfire smoke season or heavy-use winter months in Canada, inspect monthly regardless of filter type and replace when visibly grey.

How do I know when my furnace filter needs replacing?

Four reliable signs: (1) Visual check — hold the filter up to light. A new filter looks white or cream. If it's uniformly grey and you cannot see light through it, replace it immediately. (2) Increased dust — if dust is settling on furniture faster than usual, your filter is no longer capturing airborne particles effectively. (3) Reduced airflow — weak air coming from vents despite the furnace running indicates a clogged filter restricting the blower. (4) Higher energy bills — a dirty filter can reduce HVAC efficiency by up to 15%, which can meaningfully increase your monthly heating and cooling bills.  When in doubt, replace it — filters are far less expensive than HVAC service calls.

Should I change my furnace filter more often in winter in Canada?

Yes. In Ontario and other Canadian provinces, furnaces run more frequently during winter months, which means the filter traps more particles in a shorter period of time. In December through March when your furnace may run 8–12 hours per day, a filter that normally lasts 90 days in shoulder seasons may need replacement after 30–45 days. Check your filter monthly during peak heating season rather than relying on a fixed calendar schedule. If you have a smart thermostat (Ecobee, Nest), enable filter-change reminders for the winter months.

Can I clean and reuse a disposable furnace filter?

No. Most filters are disposable — washing or vacuuming can damage the filtration fibers and reduce their effectiveness. Disposable pleated filters use synthetic polymer media bonded to a cardboard frame. Water damages the media structure, reducing its particle-capture efficiency and potentially promoting mould growth when reinserted. Vacuuming loosens captured particles back into the air and can dislodge the media from its frame. The only reusable filters are those specifically labelled as washable or electrostatic — always check the manufacturer's designation before attempting to wash or reuse a filter.

Can I run my furnace without a filter temporarily?

Only for an absolute maximum of 6–8 hours in a genuine emergency. Running a furnace without a filter is not safe. Without a filter, dust and debris enter the furnace, clog internal parts, and can cause overheating or system failure. It also degrades indoor air quality. Even a few hours without a filter allows dust to accumulate on the blower motor, coils, and heat exchanger. Extended operation without a filter — overnight or over multiple days — can result in expensive cleaning or component replacement. Order a replacement filter immediately and have it installed before the next heating cycle if possible.

How often should I change a 4-inch furnace filter?

Every 6 to 12 months under normal household conditions. 4-inch deep-media filters have significantly more surface area than 1-inch filters, which means they hold substantially more dust before becoming clogged. In high-dust environments, homes with multiple pets, or during Alberta or BC wildfire smoke season, inspect every 3 months and replace when the filter face is visibly loaded. Replacing a 4-inch filter prematurely wastes money; replacing it too late strains your HVAC system and reduces air quality. The best habit is a quick visual check on the first day of each season.

Which way does a furnace filter go in?

The arrow printed on the filter frame must point toward the furnace — in the direction of airflow. Air is pulled in through the return ducts, passes through the filter, and then enters the furnace blower to be heated or cooled. The arrow should face the same direction the air is moving: into the furnace. A simple rule: the arrow always points away from the return duct and toward the furnace blower motor. If you're installing a filter in a wall return vent, the arrow should point into the duct, toward the system. Take a photo of the arrow direction before removing your old filter if you're unsure.

What happens if I install a furnace filter backward?

Installing a filter backward restricts airflow significantly. Installing a furnace filter backwards blocks airflow and allows dust and debris to sneak past the filter and into your system. Your home's air can become dirtier, and your furnace has to work harder to move air, which shortens its lifespan. Signs of a backward filter include: rooms taking longer to heat or cool, the furnace running more frequently, weak airflow from vents, or dust accumulating more quickly on furniture. If you suspect backward installation, turn off the furnace, remove the filter, confirm the arrow direction, and reinstall correctly.

How do I change a furnace filter step by step?

Six steps: (1) Turn off your furnace at the thermostat. (2) Locate the filter — typically in the blower compartment or at the return air duct. (3) Note the arrow direction on the existing filter before removing it, or photograph it. (4) Slide out the old filter and immediately place it in a plastic bag to prevent dispersal of trapped dust. (5) Insert the new filter with the arrow pointing toward the furnace blower. Ensure the filter fits snugly with no gaps around the frame. (6) Close the access panel, turn the furnace back on, and write the date of replacement on the filter frame with a marker. The entire process takes less than five minutes.

Where is the furnace filter located in my home?

In most Canadian homes the furnace filter is in one of three locations: (1) Inside the furnace cabinet, typically in the blower compartment — open the lower access door and look for the filter slot near where air enters the blower. (2) At the return air duct, either at the furnace or at a central return air grille in a hallway or utility room. (3) In a dedicated filter cabinet, common on systems with 4-inch or 5-inch deep-media housings — these typically have their own access door adjacent to the furnace. For upflow furnaces where air moves upward, the filter is located in the blower compartment bottom door adjacent to the cold air return. Remove both the top door and then the bottom door to access it. If you cannot locate your filter, check your furnace manufacturer's manual.

Should I turn off my furnace before changing the filter?

Yes, always. Turning the furnace off at the thermostat before removing the filter prevents the blower motor from pulling unfiltered air — and the loose dust cloud that comes out with the old filter — through the system and into your home while the filter slot is open. It also protects you from having the blower start unexpectedly while your hands are inside the filter compartment. Turning the furnace off takes 10 seconds. It is always worth the precaution.

Do furnace filters help with allergies?

Yes, significantly. A properly rated furnace filter is one of the most cost-effective ways to reduce airborne allergens in a Canadian home. MERV 11 filters capture fine pet dander, pollen, and mould spores — the primary triggers for seasonal and year-round allergies. MERV 13 also captures fine PM2.5 particles and airborne bacteria. For allergy sufferers, replace filters on the shorter end of the recommended schedule (every 30–45 days for 1-inch filters) to prevent the filter itself from becoming a source of recirculated allergens once saturated. During high pollen season in spring, inspect weekly.

Why is my house so dusty even after changing the filter?

Four likely causes: (1) Wrong size — if the filter is slightly too small, air bypasses the media around the edges and carries dust into your ductwork regardless of the filter's MERV rating. (2) Filter installed backward — restricts airflow and reduces capture efficiency. (3) Rating too low — a MERV 8 filter in a high-dust household with pets may not be sufficient; upgrade to MERV 11. (4) Air leaks in ductwork — if your ducts have gaps or unsealed joints, dust enters the air supply downstream of the filter entirely. If your filter size, installation, and rating are all correct and dust persists, have your ductwork inspected for leaks.

Can a clogged furnace filter cause my furnace to stop working?

Yes. A severely clogged filter restricts airflow to the point where the furnace's heat exchanger overheats and triggers the high-limit safety switch, causing the furnace to shut itself off. This is a designed safety feature — it prevents heat exchanger cracking, which is both an expensive repair and a carbon monoxide risk. If your furnace turns on briefly and then shuts off repeatedly, check the filter first before calling for service. In many cases, replacing a clogged filter resolves the shutdown cycle immediately. A well-maintained HVAC system lasts 15–20 years, but a clogged filter can drastically shorten this.

Does a furnace filter help in summer when I'm using air conditioning?

Yes — the same filter serves your air conditioning as your heating. The filter works year-round, whether you're heating in winter or cooling in summer. When your air conditioner is running, the furnace blower circulates the cooled air through your home, so the same filter is still doing the job. Summer pollen season is actually one of the heaviest loading periods for residential filters — check and replace your filter in May or June at the start of air conditioning season, not just in the fall before heating season begins.

Are United Filter furnace filters made in Canada?

Yes. United Filter manufactures its pleated furnace filters at its facility in Oakville and Mississauga, Ontario. The company was founded in 2014 and is based at 2150 Winston Park Drive, Unit 15, Oakville, Ontario. Custom-size filters are also manufactured in Mississauga. Buying directly from United Filter supports Canadian manufacturing and eliminates the OEM markup charged by big box retailers. All prices are listed in Canadian dollars (CAD).

Does United Filter ship to all Canadian provinces?

Yes. United Filter ships to all Canadian provinces and territories including Alberta, British Columbia, Ontario, Quebec, Manitoba, Saskatchewan, Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, Northwest Territories, Yukon, and Nunavut. Orders typically ship within 1–2 business days from our Oakville, Ontario facility. United Filter also ships to the United States.

What is United Filter's return policy?

United Filter offers 30-day hassle-free returns from the date of delivery. If the return is due to an error on United Filter's part — wrong item shipped, defective product, or damaged in transit — return shipping is covered by United Filter. For other returns, contact us at (905) 403-0160 (local), (844) 834-5837 (toll-free), or via the contact form at unitedfilter.com/pages/support. Confirm at unitedfilter.com/policies/refund-policy that custom-size orders are indeed final sale before publishing this claim.

What furnace filter should I use in Alberta during wildfire season?

MERV 13 is the recommended standard for Alberta homes during wildfire smoke season (June through September). Alberta's dry climate and proximity to wildfire-prone boreal forest make fine PM2.5 smoke exposure a real seasonal health risk. MERV 8 and MERV 11 filters cannot effectively capture PM2.5 particles. During non-smoke seasons in Alberta's dry winter climate, MERV 11 is typically sufficient for most homes. During wildfire events, inspect your filter weekly and replace it as soon as it turns visibly grey — smoke-loaded filters can saturate in as little as 2 weeks rather than the usual 2–3 months.

How do United Filter prices compare to Home Depot and Canadian Tire?

United Filter's pleated filters start at approximately $9.17 per filter (16×25×1 MERV 8 in a case of 6, $54.99 CAD), compared to $15–$30 per filter for equivalent ratings at Canadian Tire and Home Depot. For 4-inch deep-media filters, United Filter's cases run $64.99–$124.99 CAD depending on size and MERV rating, versus $35–$60 per single filter at big box retail. Buying in cases of 4–12 filters from United Filter reduces the per-filter cost significantly. All United Filter products are manufactured in Canada and ship free on qualifying orders — eliminating the convenience premium of in-store retail.

Can I replace my Honeywell furnace filter with a United Filter product?

Yes. United Filter manufactures OEM-compatible replacement filters for all major Honeywell whole-home air cleaner models, including the FC100A1029 (16×25×4, MERV 11), FC100A1037 (20×25×4, MERV 11), and Honeywell 5-inch models in 16×25×5 and 20×25×5. These are direct replacements that fit the same housing and deliver equivalent or better filtration performance, at a lower cost than ordering genuine Honeywell replacement filters. Match the MERV rating and actual size to your existing Honeywell filter when ordering.

Can I replace my Lennox Healthy Climate filter with a United Filter product?

Yes. United Filter stocks compatible replacements for Lennox Healthy Climate filters including the X6670 (16×25×5, MERV 11), X6672 (16×25×5, MERV 16), X6673 (20×25×5, MERV 11), and X6675 (20×25×5, MERV 16). For MERV 11 replacements, United Filter's compatible 5-inch filters in the correct actual depth (4⅜", 4⅞", or 5¼") fit the Lennox housing and provide equivalent performance. Genuine Lennox OEM filters are also available through United Filter for customers who require original equipment. Confirm your filter's actual dimensions before ordering.

Does United Filter sell commercial HVAC filters?

Yes. United Filter supplies three commercial filter lines: (1) Pocket bag filters — MERV 11, 13, and 15 secondary/final-stage filters for constant-airflow commercial HVAC systems including offices, hospitals, hotels, data centres, and industrial facilities. (2) Rigid box filters — commercial secondary filters for Variable Air Volume (VAV) systems where airflow speeds vary and pocket bag filters would collapse. (3) HEPA filters — 99.97% efficiency commercial filters for hospitals, laboratories, pharmaceutical facilities, and clean rooms, available in 95%, 99.97%, and 99.99% efficiency grades and rated to 220°F standard or 500°F for high-temperature applications. Contact (905) 403-0160 for commercial pricing and specifications.

What is the GeneralAire M1-1056 filter, and can I get a replacement from United Filter?

The GeneralAire M1-1056 (also sold under the AMP M1-1056 designation) is a 16×25×5 deep-media pleated filter used in GeneralAire, York, Electro-Air, Cinquartz, and Direct Energy whole-home air cleaner systems. United Filter carries both genuine OEM M1-1056 filters and compatible replacement versions in MERV 11 and MERV 13 ratings, available in cases of 1, 2, 3, and 4. The compatible replacements deliver equivalent filtration performance at a lower cost than the OEM version. Available at unitedfilter.com or by calling (905) 403-0160.