For most houses, the general rule is to replace your furnace filter every 1 to 3 months. Your actual timeline for changing your furnace filter is based on a various factors such as household size, air quality, pets, and more. Knowing when to change your furnace filter is one of the easiest and cheapest ways to make your furnace more efficient, lower your energy bill, and protect your home’s HVAC system.
This guide will teach you exactly how often you should change your furnace filter, what factors influence your timeline, and warning signs that your furnace filter is dirty.
Short Answer
Even though there is no one answer for when you should change your furnace filter, for most Canadians, every 90 days is standard and 30-60 days for households with pets. Before you decide that every 90 days is good enough, you should consider your filter type. Most Canadians use a 16×25 inch pleated filter that’s one inch thick. A larger number of people and pets and prevalence of allergy will also shorten your timeline for replacing your furnace filter.
What Factors Affect Your Furnace Filter Replacement Schedule?
Filter Type
Not every filter is the exact same. Thinner filters have less surface area to trap debris in the air, meaning they clog faster. If you’re changing your filter more than you want to, consider upgrading to a thicker filter. Below is a quick reference chart for different sized furnace filters.
| Filter Thickness | Average Lifespan |
| 1-inch pleated (Most common for Canadians) | 60-90 days |
| 1-inch fiberglass | 30 days |
| 3-4 inch pleated | 6-9 months |
| 5 inch | 6-12 months |
How Pets Reduce Furnace Filter Lifespan
For pet owners, shed fur is one of the primary causes of filter clogs. Even a single pet shedding daily can nearly cut your funarce filter’s lifespan in half. If you have one or a few pets, replace your filter more often, likely every 60 days. Many pets that shed heavily may require monthly filter changes.
How Often the Furnace Runs
Furnace filters get dirty from air passing through them. In most parts of Canada, long, cold winters leave furnaces running almost constantly for months. This wears out furnace filters faster than in warmer climates where the system cycles less frequently. Considering this, you should check your filter more often in the winter when your furnace is running more.
How Household Size Affects Furnace Filter Lifespan
With each person in a home comes more dust, skin cells, and debris getting caught in the furnace filter. If you live in a house with many people, consider checking your furnace filter more often. Changing your filter more frequently can reduce reactions from allergies, asthma, or any other respiratory issues.
How to Change Your Furnace Filter in 3 Steps
Make Sure Furnace Isn’t Running
Make sure your furnace is either not running, or turn off the system via your power switch or thermostat. You want to make sure air isn’t passing through without a filter.
Locate and Remove the Filter
Your furnace filter is most likely located in a narrow metal slot by the furnace. Slide out the filter, find the arrows on the frame, and remember their direction. Remember that air always flows from your home ducts into the furnace.
Insert New Filter
Before putting in your new filter, ensure that it fits the exact dimensions of your dirty one. If it matches, insert the new air filter with the arrows pointing the same direction as the old filter (pointing towards the furnace fan).
If you turned off your furnace beforehand, turn it back on. It’s also worth considering writing down the date somewhere (even on the filter frame) so you can keep a close track of your filter schedule.
Immediate Signs to Change Your Filter
Visible Dust or Buildup on Furnace Filter
If you remove your filter and see a layer of dust, lint, or fur, swap it out. An easy test is to hold your filter up to a light. If you can’t see any light through it, replace it immediately.
Stale or Burning Smell
If your heat kicks on and you get a stale, burning, or musty smell, that means dust buildup is causing overheating. This is an immediate sign to replace your filter.
Uneven Heating
If your furnace struggles to heat up rooms further away from it, your filter may be clogged. A clogged filter will make it hard for your furnace fan to push air through it.
Higher Energy Bill
A dirty furnace filter will force your furnace fan to blow harder and run longer to heat your house up. If you experience a sudden spike in your power bill, your filter may need to be changed.
Frequently Asked Questions
How do MERV ratings work?
MERV (Minimum Efficiency Reporting Value) measures how well a filter captures debris in the air. You should use the MERV rating recommended by your furnace or manufacturer to decide what furnace filter to buy. A higher MERV rating means that the filter can trap smaller particles with more airflow resistance. 1-4 is the least effective filter, 5-8 is a standard choice for most homes, 9-12 will capture debris better, and 13+ is generally not suitable for most furnaces at home.
Which way should the arrow face on my furnace filter?
The arrow on your furnace filter should always point towards your furnace. If you put your filter in backwards, it will be less efficient and strain your HVAC system.
Can I run my furnace without a filter?
You should never run your furnace without a filter. Without a filter, debris will collect and will probably result in needing expensive repairs. If you don’t have a filter, put one in as soon as possible to prevent damaging your furnace.
Can I wash my furnace filter?
For most filters, you should never wash them. Most household furnaces use disposable filters, which means you need to replace them when they’re dirty. Some filters are reusable and you can rinse them, let them dry off completely, and reinstall them.
Why does my furnace filter get dirty so fast?
Many reasons can cause a furnace filter’s lifespan to shorten. More people and pets will cause more buildup of debris on the filter. Even having one or two pets shedding can reduce a filter’s lifespan a lot. If your furnace is running very often, especially when it’s colder out, more air is passing through your filter, which means it will get dirty faster. Renovations or construction can also create a lot of dust and debris buildup. It’s worth checking your filter shortly after renovations. If your filter is getting dirty unusually fast, it may be worth considering getting your HVAC system inspected.
What is the difference between pleated filters and fiberglass filters?
Pleated filters are found in the majority of Canadian homes. They typically have a MERV rating of 8-11 and are better at capturing dust, pollen, pet fur, and everything else. In Canada, you can usually find pleated filters at stores such as Canadian Tire, Home Depot, RONA, or Costco. Fiberglass filters are less common and much cheaper. They don’t actually improve indoor air quality much, but are a cheaper option for properties to just protect the furnace.