The Truth About Furnace Filters
Quick answer
For most Edmonton homes, a pleated filter rated MERV 8 to 11 is the best balance of clean air and good airflow. Go up to MERV 11 to 13 if you have pets or allergies. Check a standard 1-inch filter every 1 to 3 months during heating season, and change it when it looks dirty.
First, what does MERV mean?
Most furnace filters are rated on the MERV scale (Minimum Efficiency Reporting Value), from 1 to 16. The higher the number, the smaller the particles it catches.
- MERV 1 to 4: catches larger dust and lint. Basic protection for the furnace.
- MERV 5 to 8: catches pollen, dust mites and mould spores.
- MERV 9 to 13: catches finer particles like pet dander and some smoke. Great for allergy sufferers.
- MERV 14 to 16: very fine filtration, but it can restrict airflow on many home furnaces.
For scale: a human hair is about 80 to 100 microns, pollen about 30, dust about 10, pet dander about 5 and smoke about 1. Anything under about 40 microns is invisible to the eye.
The 7 common filter types
| Filter type | Best for | Watch out for |
|---|---|---|
| Pleated | Most homes; wide range of MERV ratings | Needs regular replacing |
| Spun glass (fibreglass) | Lowest price; protects the furnace | Does little for air quality |
| Washable | Buy once, less waste | Must be cleaned and fully dry, or it grows mould |
| Electrostatic | Affordable; washable versions last years | Less effective on very fine particles |
| Media (4 to 5 inch) | Excellent filtration, changed 1 to 2 times a year | Needs a cabinet, professionally installed |
| HEPA | The finest filtration available | Too dense for most furnaces; needs a separate system |
| UV light | Kills bacteria, viruses and mould | An add-on, not a filter; doesn't catch dust |
What you can safely check yourself
- Find your size: it's printed on the edge of your current filter (for example, 16x25x1).
- Check the arrow: the airflow arrow on the filter points toward the furnace.
- Look at it: hold it up to a light. If you can't see through it, change it.
- Date it: write the install date on the edge, so you always know when it was last changed.
- Check more often if you have pets, allergies or renovation dust in the house.
When to call a professional
Call a licensed technician if:
- You'd like a high-MERV, HEPA or media filter and aren't sure your furnace can handle it
- You want a UV light or media filter cabinet installed
- Your filter gets dirty unusually fast
- Airflow is weak even with a clean filter
- You can't find your filter slot, or the filter doesn't fit snugly
How SS Plumbing & Heating handles it
We'll look at your furnace, your home and your family's needs (allergies, pets, asthma) and recommend the right filter, not the most expensive one. Every 20-point tune-up includes a filter check.
Don't want to keep track? We offer furnace filter delivery every 3, 6 or 9 months, so the right filter shows up at your door when it's time.
A Few Questions We Get a Lot
Is a higher MERV rating always better? No. A very dense filter can choke airflow on some furnaces, which makes them work harder. For most homes, MERV 8 to 11 is the sweet spot.
Can a dirty filter really cause furnace problems? Yes. A clogged filter can make the furnace overheat and shut off, and it wears out the blower. See 5 Common Furnace Problems and Why Is My Furnace Running but Not Heating?
Should I run my furnace without a filter for a day? Please don't. Even a short time lets dust coat the blower and other parts inside.
Not sure which filter is right for you?
Every home is different. Call or text us for a free phone consultation, or set up filter delivery and never think about it again.
About Steve
Steve St. Louis is a Red Seal Journeyman Plumber and Gasfitter (Class B) and the owner of SS Plumbing & Heating Ltd. Based in Sturgeon County, Steve and his team have served Edmonton and area since 2020, with 24/7 emergency service and a 5.0 rating from 450+ Google reviews.