Furnace filters: tips and advice

Learn all about furnace filters

The furnace filters play a significant role in the quality of your inside air. How to choose them? When to replace them? Which MERV rating is best for your home? How to extend their lifespan? The tips and advice that follows will help you make the right choice.

Filtration system quick overview

The main goal of filtration is removing contaminants from being recirculated in the air. Accordingly, the heating and cooling devices recirculate and filter the air, like many air changes per hour. Many filtration levels are possible depending on the type of filter you’re using.

What is the MERV rating?

The MERV rating – Minimum Efficiency Reporting Value – is a standard that rates the overall effectiveness of air filters. The (ASHRAE) established the ratings system to guide you in your choice of filters.  Higher value MERV rating equates to finer filtration, meaning fewer dust particles and other airborne contaminants can pass through the filter.

A MERV rating tells you, on a scale of 1-16, how effectively your filter traps the small particles you don’t want circulating through your home.

MERV rating scale

# of the groupMERV


Average efficiency
0.3 – 1.0 Microns
Average efficiency
1.0 – 3.0 Microns
Average efficiency
3.0 – 10.0 Microns
Filtration capacity
(ASHRAE 52.1)
(per group)

Less than 20%
Less than 20%
Less than 20%
Less than 20%
Less than 65%
65 – 69.9%
70 – 74.9%
75% or more
Pollen, mites
sanding dust
textile fiber
carpet fiber

20% – 34.9%
35% – 49.9%
50% – 69.9%
70% – 84.9%

Molds, spores
Pet hair
Virus, Formaldehyde
+ Group 1

Less than 50%
50% – 64.9%
65% – 79.9%
80% – 89.9%
85% or more
85% or more
85% or more
90% or more

common bacteria
Cigarette smoke
+ Group 2
4MERV 13
Less than 75%
75% – 84.9%
85% – 94.9%
95% or more
90% or more
90% or more
90% or more
95% or more
90% or more
90% or more
90% or more
95% or more

paint dust
smoke dust
+ Group 3

When to change your furnace filters?

The main factors influencing the lifespan of the furnace filters are:

the quality of the furnace filter, the thickness of the filter and the amount of dust in the home.

View all of our furnace filters

1″ furnace filters
Lifespan every month

2″ furnace filters
Lifespan 1-2 months

4″ furnace filters
Lifespan 3-5 months

5″ furnace filters
Lifespan 3-5 months

Extend the lifespan of your filters

Yes, a simple regular cleaning will help extend the life of your furnace filters!  Here’s how to do it:

  1. Every week, get rid of the dust that’s stuck around the opening of the intake of the filter, with a vacuum cleaner. You’ll extend the lifespan of your filters of about one month. Make sure you don’t scrub the filter, to keep it in good condition*.
  2. Because the pleats of the 4’’ and 5’’ are deeper thant the smaller filters, this technique would be more appropriated than the first one. Use a table spoon or your fingers to clean inside the pleats of the pleated filters. Do that once a week, and you will expand their lifespan of about one month.
  3. After using the techniques 1 or 2, if you find that the dust is not completely removed from the filter, bring it outside and shake it in the same direction that the air would blow (where the dust is stuck). That will really help extend the lifespan of your filters*.

Other tips to save money

Did you know that the furnace filters we sell are of higher quality then those offered in major stores? Not only are they of professional quality, but are also available at a better price. Buying advice: choose to buy in bigger quantities to save money. That way you’ll have more money in you pocket and you won’t have to reorder so soon.

What is air quality?

It’s far from the city, and from the outdoor pollution, that we find the purest of air. Sadly, the indoor air is not so pure as in the forest, the fields or the mountains. Indoor, many contaminant source are present. The building of your house represent the highest level of indoor pollution! The building of the walls, the paint, the isolating material in the walls, the carpets, the flooring, the building material, your kitchen cabinets, the couch and recliner. All these elements represent a potential danger of deteriorating the indoor air quality. In the words of the air quality specialists, we call them the formaldehyde.

The risks linked to poor air quality

Did you know that the indoor air that we breath can be more polluted than the outdoor air?

The risks linked to air pollution are now more important than we thought. The cooling and heating devices greatly impact the air quality, among others, the particle pollution.

The air and your health

Everyone reacts differently to a bad quality of indoor air. Every problem has to be dealth with carefully, because the most sensitive people can end up with severe breathing illnesses like lung cancer, chronic asthma, legionellosis, sarcoidosis, and many more. You might not feel the effects in a short term period. But, in the long term, a bad indoor air quality can be devastating for the health of the occupants.

If you have an oil furnace or natural gaz furnace, the use of a filter is even more important to filter the fumes from combustion. Moreover, to take good care of your cooling and heating devices is a good way to increase the quality of your indoor air.

Not so fine particles

The fine particles are made of solid dust or suspended in the air, like dirt, grime, fumes or volatile organic compounds. Their structure can absorb other toxic substances with very negative consequences for the health. In 2012, one in eight deaths is due to pollution (indoor and outdoor) in the world.

Identify the pollutants

Tobacco smoke:

Residues from the secondhand and thirdhand with long term impact.


Radioactive extremely dangerous gaz frequently present in our environment. It is the result of the decay of uranium in the ground, rocks, and water. It’s a colourless, and odourless gas.


A colourless gaz with a typical chemical odor from the construction products, household products, and other non green products.


Microscopic element coming from animals or mites.

Carbon monoxide:

The smoke coming from the wood combustion can be a source of emission.

Humidity and mildew:

Fungi and bacterias suspended in the air when there is enough humidity.

Chemical products:

Household products, candles, incense, crafting products and renovation.

The importance of an air filter

Your air filter is your only way to filter your indoor air (an air exchanger is not a filter, it gives fresh air from outside which is partially filtered). The air pulsed by your furnace or heating, ventilating and cooling device (HVAC), travels in your home and is mixed with the active pollutants inside. A bad or neglected filter  will badly affect the quality of the air, because the breathing of the occupants or the presence of Formaldehyde multiply the carbon monoxide activity.

Need help to choose and order your filters: contact us!

* All the techniques work only on quality furnace filters.