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Why is Regular Furnace Filter Replacement Important?

Last Updated: September 18, 2021

Written on April 12, 2018 by Karen Norman
Why Furnace Filter Replacement is necessary

Why are Furnace Filters necessary?

Read on for the importance of Furnace Filters and 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 the key 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 full.

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?

Furnace Filters can differ in size, quality, efficiency, and filtering processes. The level of dust entrapment combined with air flow 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 air flow. In doing so, it may harm your HVAC system.

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

Understanding MERV Ratings.

Background on MERV Ratings.

First some rather boring background on MERV Ratings. MERV ratings are measure in μm. μm is the symbol for a micrometer 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 is actually 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, I repeat, the highest rating will not be the best for your furnace even if it is a more effective filter. In an 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 filters efficiency. The Dust Holding Capacity is simply a measurement of the amount of dust a filter can hold.

The significance of MERV Ratings.

Essentially the MERV ratings determine the size of particle that can be filtered. See options below. At the time of writing (which is during the COVID-19 pandemic), ASHRAE  recommends using MERV 13 or better yet 14 but that is subject to the abilities of each HVAC system. If your system will 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 (Microparticle Performance Rating).

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

Home Depot in Canada outlines their ratings are 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 Rating is better? 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), and then look at costs and lifespan and do some experimenting. Often it is simply a matter of personal choice.

How to choose from the different types of Furnace Filters.

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.

Flat Panel Filters.

Flat Panel Filters are mostly made of stretched fiberglass 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 is 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. 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. Although 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 paneled or pleated. These filters can be washed with running water or vacuumed.

HEPA (High Efficiency Particulate Air) Filters.

HEPA Filters 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 do you need?

First there is no one standard size filter. There are 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. However, 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 your 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. 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 air flow.
  • Replace the compartment cover.
  • Turn the furnace on again and remember to turn the thermostat back up.

When to change your Furnace Filter? How Often?

Once a furnace filter is dirty, it blocks the air flow 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.

Nine more reasons your Furnace Filter might need changing.

  • Moving into you New Home

    • Whether it is a brand-new home or a home new to you, you just might want to change that filter. 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-block with dust and drywall.
    • For that matter you might want to check if the furnace and ducts need cleaning too.
    • If it is just a new home to you, why not start things off right and at least 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 make sure your new living space is disinfected?
  • Calgary Winters

    • With the long, extreme cold Calgary winters your furnace can be working overtime. Checking on your furnace filters more often is recommended.
  • Calgary Summers

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

    • Pet dander and fur can accumulate significantly in the ductwork. If you have a cat or dog that sheds a lot of either fur or dandruff your filter will need changing that much sooner.
  • A Full Household

    • A household full of children in particular, may mean more outdoor traffic bringing dirt and pollen indoors.
  • Being at home more through Pandemics

    • Pandemics such as COVID-19 might mean your whole household is simply home more. It stands to reason that your furnace filter will need changing sooner.
  • Smoke

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

    • Fine paint spray particles, 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 air flow. However, if you do, you will need to replace your filters more frequently.
    • Constant use of the fan will mean more air moved through the filter and it will get dirty sooner.

Ways to remember to change the Furnace Filter.

If you change the filter at Daylight Savings 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 usage and life of the filter remaining through an App.

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

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!

Benefits of Regular Furnace Filter Replacement.

  • A Cleaner Furnace System.

When Filters are preventing the muck and grime 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 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 less 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.

  • Less likelihood of Breakdowns – Read our story!

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

One morning a few years ago now, I noticed that the house was considerably colder than normal. On checking the thermostat, it was set where it always is in the cooler months at around 22 centigrade. Worryingly our home was not reaching the 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 Official Plumbing and Heating in Calgary to investigate the issue. They are one of the companies we recommend for furnace repair issues as we at Dang Good currently focus on Furnace and Duct Cleaning not repairs. 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 brown grimy filter in the picture above was ours! 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 excess of use. Fortunately, we just needed the filter changed but of course we had to pay the technician a call-out charge.

We paid a costly price. Neglecting such simple maintenance on our HVAC system, when a regular filter change would have been a much cheaper way to go. 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 provides a Free basic standard Furnace Filter Replacement with each furnace and duct cleaning service.

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

What if you are forever changing that Furnace Filter?

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

Alternatively, you may be long overdue for a furnace and duct cleaning. It could be that dust, debris and bacteria are accumulating in the duct work. Please feel free to give us a call at: 403-984-3680 if you are needing a cleaning service.

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