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Why changing your Furnace Filter is Important

Last Updated: April 8, 2024

Written by Karen Norman
Why Furnace Filter Replacement is necessary

Are Furnace Filters necessary? 

Read on for the importance of Furnace Filters and the consequences of not changing them!

Have you ever wondered why your furnace needs a filter? A Clean Furnace Filter protects the various elements of your Furnace. It also helps improve Indoor Air Quality too. The filter collects dust, hair and debris that could clog up critical components needed to keep your heating system working efficiently.

A dirty Furnace Filter, on the other hand, restricts airflow. Furnace filters were designed to allow airflow and will do just that, provided they do not get too clogged up with dirt.

So yes, your Furnace needs a Filter to keep it running effectively, and it needs a clean one to boot.

How to choose a Furnace Filter? 

Choosing the furnace filter type will depend on the requirements of the furnace manufacturer. Check the operating manual or seek out information on the model of your furnace online. Furnace Filters can differ in size, quality, efficiency, and filtering processes. In addition, the level of dust entrapment combined with airflow can vary from one filter to another. Filters are generally measured by the industry standard known as MERV, created by ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers).

However, a higher MERV rating is not always the best. MERV stands for Minimum Efficiency Reporting Value. If you get a filter with too high a rating, although it may be more efficient at trapping contaminates, it can hinder airflow. In doing so, it may harm your HVAC system.

An alternative measurement is the 3M™ Filtrete™ MPR (Microparticle Performance Rating).

Understanding MERV Ratings. 

About MERV Ratings. 

First, here is some rather boring background on MERV Ratings. MERV ratings are measured in μm. μm is the symbol for a micrometre or micron, and one micron is one-millionth of a meter. It is used to measure the diameter of airborne particles.

MERV Ratings range from 1 to 16. However, some suggest the range should be 1 to 20. A moot point, really, as furnace filters would not usually be that high a rating. Each MERV rating indicates the percentage to which a furnace filter can protect against 0.3 to 10 micron (10-6m) particles.

However, the highest rating will not be the best for your furnace, even if it is a more effective filter. In the article: “All about MERV Ratings,” FilterBuy Inc advises that carpet fibres are more than 10 microns whereas bacteria are less than 0.3 microns.

MERV ratings are also determined by the Arrestance Test and the Dust Holding Capacity. The Arrestance Test is the ability to remove synthetic dust used to measure a filter’s efficiency. The Dust Holding Capacity is simply a measurement of the amount of dust a filter can hold.

Choosing MERV Ratings. 

Essentially the MERV ratings determine the size of particle that can be filtered. See options below. At the time of writing, ASHRAE  recommends using MERV 13 or, better yet, 14, but that is subject to the abilities of each HVAC system. If your system does not support MERV 13, they suggest going with the highest rating possible. Locally, consumers tend to find working with MERV ratings 5-8 the most economically efficient for their systems.

Below is an indication of the filtering capability according to MERV ratings.

  • MERV Rating 1-4 – Least Effective – Lint, Pollen, sanding dust, Bugs, carpet fibres, spray paint dust.
  • MERV Rating 5-8 – Moderately Effective Mold spores, cement dust, hair spray, dust mites, pet dander.
  • MERV Rating 9-12 – Highly Effective – auto emissions, milled flour, fumes, lead dust.
  • MERV Rating 13-16 – Most Effective (if your system supports it) – Bacteria, Tobacco smoke, microscopic allergens.

3M™ Filtrete™ MPR Ratings. 

3M™ Filtrete™ created the MPR (Microparticle Performance Rating) measurement system. The emphasis is on microparticles which do not enter the equation on the MERV scale until MERV 11. MPR focuses on capturing particles between 0.3 and 1 micron, such as bacteria or cough and sneeze particles. According to 3M™, Filtrete™ filters handle air resistance better.

Home Depot in Canada outlines its ratings as follows:

  • MPR Rating 600 or less – Economy – dust/lint, pollen, virus carriers, microscopic allergens, dust mite.
  • MPR Rating 600 to 1200 – Good – includes all in ‘Economy’ plus odour.
  • MPR Rating 1201 to 1899 – Better – includes all in ‘Good’ plus pet dander.
  • MPR Rating 1900 to 2199 – Best – includes all in ‘better’ plus most smoke.
  • MPR Rating 2200 and above – Premium – includes all in ‘best’ plus Mold Spores, Smog Particles and Bacteria.

Which is best: MERV or MPR? 

It is hard to give a definitive answer when comparing filters that use the MERV rating over the MPR scale. The MPR scale is unique to 3M™ Filtrete™, and as far as we know, it has not been tested by 3rd parties. Yet MERV is still currently the industry standard.

Additionally, each rating system takes a slightly different approach, although their outcomes are designed to be similar. Our best suggestion is to select filters based on what they claim to do (HVAC System capabilities notwithstanding), then look at costs and lifespan and experiment. Often it is simply a matter of personal choice.

Flat Panel Filters. 

Flat Panel Filters are mostly made of stretched fibreglass fibres. They are inexpensive, affordable, and disposable. Installation is easy. However, they are not usually the best quality, letting many particles through. Their MERV ratings are typically 2 or 3. They also do not tend to last long and need changing out sooner. Do not attempt to clean a disposable filter.

Pleated Disposable Filters. 

As the name suggests, these filters have pleats which are better for filtration. Their screens are thicker and are made of cotton or polyester. They are marginally higher priced than the Flat Panel Filters but tend to last longer. Some suggest up to 90 days. Pleated Filters also come in a Higher Efficiency version too. MERV ratings for the regular filter are around a 6-8 and the higher efficiency model 14-16. However, you would need to ensure your furnace could withstand a higher MERV rating.

Electrostatic Filters. 

These filters are electrostatically charged and supposedly more able to collect smaller particles. They come in flat, pleated, disposable or washable. However, washable ones tend to lose some of their electrostatic charge over time. MERV ratings range from 8 to 10.

Washable Filters. 

Washable Filters can be flat-panelled or pleated. These filters can be washed with running water or vacuumed clean.

HEPA Filters. 

HEPA Filters (High-Efficiency Particulate Air) are sometimes used in homes with allergy sufferers. Although they are more commonly used in hospitals. However, you would need to check whether your furnace system can operate efficiently with the density of a HEPA Filter. MERV ratings are 16 and over.

What size filter is needed? 

First, there is no one standard size filter. Instead, there is a range of sizes. For a list of all the sizes, please see “What are the Most Common Air Sizes?” Assuming the current filter in your furnace is the right fit, then the sizing details will be on the side of the frame of the current one. Alternatively, refer to the furnace operating manual for the correct size.

Where is the Furnace Filter located? 

The best way to locate the housing of the existing filter is to check the furnace manual. Nevertheless, the filter is usually located close to the return air duct and blower fan between the cold air return and the furnace.

Alternatively, it may be in the ductwork near the blower fan. There are a few different places it could be. Please see “How to Find the Air Filter for the HVAC System in your Home,” where several options are detailed.

How to Change a Furnace Filter? 

  • First, turn off your furnace. You may also wish to turn the thermostat down temporarily to stop the blower fan.
  • Locate the existing filter. As mentioned above, this will vary in each model. Generally, it is housed between the return air intake and the furnace.
  • Remove the compartment cover if there is one.
  • Lift out the old filter and check the size, either by measuring it or by finding the dimensions on the side of the frame.
  • Make sure your new filter is the same size. Locate the arrows on the new filter.
  • Now slide in a new same-sized filter with the arrows on the frame pointing toward the furnace in the direction of the airflow.
  • Replace the compartment cover.
  • Turn the furnace on again, and remember to turn the thermostat back up.
  • If you need more visual guidance on changing your filter check out this Video by Reliance Home Comfort. 

When to change the Furnace Filter? 

Once a furnace filter is dirty, it blocks the airflow making your furnace work harder. Your filter needs to be changed before it hampers airflow. See our anecdote below.

We suggest checking your filter every month and replacing it if necessary. In addition, routinely replace it every three months regardless.

The furnace filters you buy may indicate how long they are likely to last before a new one is necessary. Even so, several factors will affect the frequency of furnace filter replacement.

Other Reasons for Furnace Filter Replacement. 

  • Moving into your New Home

    • Whether it is a brand-new home or a home new to you, you might want to change that filter on moving in. Newly built homes have probably had a lot of renovations and construction done after the furnace installation, and you may well find that your furnace is choc-a-bloc with dust and drywall.
    • For that matter, you might want to check if the furnace and ducts need cleaning too. You can find out more about the process in our Guide to Air Vent Cleaning.
    • If it is just a new home to you, why not start things off right and have peace of mind, knowing you have done at least one thing that will help keep your furnace working efficiently. Have you thought about Sanitizing the Ductwork or Sanitizing the Whole Home to ensure your new living space is disinfected?
  • Harsh Winters

    • Long, extreme cold winters such as those in Calgary, your furnace can be working overtime. Therefore, checking on your furnace filters more often is recommended.
  • Hot Summers

    • We tend to bring a lot of the outside in when we open our homes up during the warmer months. So, unfortunately, we tend to bring in more dust and pollen.
  • Pets

    • Pet dander and fur can accumulate significantly in the ductwork. So if you have a cat or dog that sheds a lot of hair or dandruff, you will need to change your filter that much sooner.
  • A Full Household

    • In particular, a household full of children may mean more outdoor traffic bringing dirt and pollen indoors.
  • At home through Pandemics

    • Pandemics such as COVID-19 might mean your whole household is home more. So it stands to reason that your furnace filter will need to be changed sooner.
  • Smoke

    • Tobacco smoke and smoke from wood-burning stoves and fireplaces will affect the lifespan of your filter.
  • Renovations

    • Fine paint spray particles and drywall dust may make extra filter changeout necessary.
  • Running the Fan Continuously

    • You may wish to run the fan constantly. There is certainly an argument to be made for better filtration and airflow. However, you will need to replace your filters more frequently if you do.
    • Constant fan use will mean more air moved through the filter, and it will get dirty sooner.

Remembering to change the Furnace Filter. 

If you change the filter during Daylight Saving Time, you will have at least done two out of the three quarterly minimum change requirements.

Some filters, such as the Filtrete™ Smart HVAC Air Filter, provide information on the usage and life of the filter remaining through an App.

Writing on the filter may help, as well as setting a calendar reminder.

Benefits of Regular Furnace Filter Replacement. 

  • A Cleaner Furnace System. 

When Filters are preventing muck and grime from entering the heating system, you may be able to go longer spells before needing a furnace and duct cleaning.

  • Indoor Air Quality. 

Filters help prevent dust, pollen and bacteria from becoming airborne and entering the home. See more on Ways to improve Indoor Air Quality.

  • Energy Savings. 

Clean filters help your furnace operate efficiently, and subsequently, they do not need to work as hard.

  • Savings on Heating Costs. 

Less energy used ultimately means fewer dollars spent.

  • Increased Lifespan of your System. 

When parts are not struggling to run smoothly, the components of your furnace will not wear out so quickly.

What happens if you do not change your Furnace Filter? 

Not having a furnace filter installed would mean that airborne particles start to clog up heating coils and fans and detrimentally impact the operation of your furnace. Not a good idea!

Avoid a Breakdown – Our story! 

This personal anecdote alone should convince you that changing your Furnace Filter is essential.

One morning a few years ago, I noticed that the house was considerably colder than usual. On checking the thermostat, it was set where it always is in the cooler months at around 22 centigrade. Yet, worryingly our home was not reaching that set temperature.

In the next hour, I noticed that the furnace and fan would kick in intermittently, and the temperature in the house was subsequently going up and down but still not reaching 22 centigrade.

My next job was to call out a Plumbing and Heating Company in Calgary to investigate the issue. They came out the same day.

Embarrassingly, it was a simple issue and somewhat shameful given that we are in the business of cleaning Furnace and Air Ducts! The problem was a Dirty Filter that should have been replaced months ago!

Yes, that grimy brown filter in the picture above was ours! Unfortunately, it was so clogged that the air was not getting through properly, and the furnace system was overheating and cutting out.

At best, this would have increased our energy costs because the furnace would not be working very efficiently. At worst, it was a potential fire hazard for sure!

We were lucky that we did not need the heat sensor replaced from excessive use. Fortunately, we just needed the filter changed, but we had to pay the technician a call-out charge.

We paid a costly price but it could have been worse! Neglecting such simple maintenance on our HVAC system when a regular filter change would have been much cheaper. How ironic given that we are:

Dang Good Carpet and Furnace Cleaning.

We have no excuse either. Dang Good keeps a constant stock of filters because Dang Good usually provides a Free Basic Standard Replacement Furnace Filter with each furnace and duct cleaning service.

All we can say is that we had been so busy looking after our customer’s homes that we neglected our own home, which is not good.

What if you are forever changing that Furnace Filter? 

Finally, if your filter seems to be getting dirty too frequently, you could try switching to a better quality or higher-rated one.

Disposing of your Furnace Filter. 

If you live in Calgary, the City has some tips on Garbage – What goes where?

Alternatively, you may be long overdue for a furnace and duct cleaning. It could be that dust, debris, and bacteria have accumulated in the ductwork. 

Please feel free to call us at 403-984-3680 if you need a cleaning service.

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