Answers to Frequently Asked Questions

The exact recommended time for changing your furnace filter will vary depending on a few different factors. For example, smaller homes with smaller families and no pets will need their filter changed a little less often than larger homes with bigger families and pets. This is simply due to the reduced amount of dust and dander generated by daily activity inside the home. Furnace filters have a limited lifespan, and as they capture more and more dust and airborne contaminants, they will eventually become less efficient the more loaded they become.

In general, the average household can expect a recommended filter change interval of about 3 months. A useful rule of thumb here is to change the filter with the changing of the seasons. Even so, it’s advisable to check the state of the furnace filter once every 1-2 months to gauge how dirty it is. If you find the filter to be dirtier than expected during these spot checks, then don’t wait until the 3 months is up. You’re better off to change it now to keep the air cleaner and your furnace operating efficiently.

In most cases the furnace filter size will be prominently printed directly on the outer casing of the filter itself. If you’re not sure exactly what size of filter your furnace may need, this is the first thing to check. In case the filter sizing is not visible on the current filter, you can refer to your furnace owner’s manual for the filter specifications. In the event that you don’t have the manual handy, most modern furnace manufacturers will have these manuals available digitally on their websites.

Jot down the make and model of the furnace, and head to your computer or smartphone to visit the support section of the manufacturers website. Most of these will have a search function available to make it easy to locate the manual for your HVAC equipment, but you can also choose to contact them directly for assistance. If you’re still coming up short on finding the filter size, you can manually measure the filter to determine this.

To properly measure a furnace filter, you will want to use a tape measure with imperial units (inches) on it, as the vast majority of commercial replacement furnace filters use inches as their default unit of measurement. Start by measuring each of the three dimensions on the outer edges of the furnace filter; width, length, and depth. It’s important to note that the exact measurements you take will likely not be perfect 1” increments, but this is normal. For example, if the exact measurements of your filter are something like 15 ½” x 23 ¾” x ¾”, then simply round each dimension up to the nearest whole inch, in this case 16x24x1. This is the standard size for that particular model of furnace, and this is what you’ll look for when shopping for replacement filters.

Read our blog article on selecting the right filter size - and our guide to selecting the correct sized filter.

There is in fact a right way and a wrong way to install a furnace air filter. The proper orientation of the air filter depends on which direction the air is moving through it. It is standard for home furnaces to filter the air BEFORE it enters the furnace. This means that it is situated in the ductwork that brings the air into the furnace, which helps you identify the direction of airflow for your HVAC system. Now, simply examine the outside of the filter to locate an arrow marking. This arrow indicates the proper direction of air to flow through the filter. Install the filter so that the arrow points towards the furnace, matching the direction of the airflow.

Installing the air filter the right way helps ensure optimum efficiency in how the filter captures airborne contaminants like dust, pet dander, and other particles. In some filters that use multiple layers to filter out particles of increasingly small size, positioning it the wrong way can shorten the filter's useful life and cause it to build up resistance at a faster rate. Always make sure you’ve got your filter installed properly to get the best performance out of it and the longest life.

Browse through any selection of air filters and you’ll most likely see the word ‘MERV’ appear quite often. This is an important designation for air filters, as it relates to how efficient the filter is in capturing airborne particles. MERV stands for Minimum Efficiency Reporting Value, and refers specifically to how efficient an air filter is at capturing particles that range in size from 0.3 microns up to 10 microns. MERV ratings start a 1 and can go as high as 16, with a higher number representing a better capture efficiency. Basically, the higher the MERV rating, the cleaner the air.

In most cases, furnace filters for home and residential use come in at a standard MERV rating of about 6-8. This is sufficient to capture common airborne particles like house dust, pollen, lint, carpet fibers, and mold spores. Filters with MERV ratings of 9-11 are better at capturing finer dust particles and do a better job of controlling airborne allergens like pet dander.

It’s important to note that as MERV rating goes up, the air resistance of the filter goes up, too. This is because if the filter is to capture those tiny particles, it needs to have a tighter mesh of fibers, which makes it harder for the air to move through the filter. This is why residential furnace air filters are usually rated no more than 13 or 14 on the MERV scale, as anything higher can reduce the energy efficiency of the furnace and restrict the proper circulation of air through the house.

Another term that you’ll see quite regularly in the world of air filtration and home comfort is HEPA filter. This stands for High Efficiency Particulate Air filter, and is used to refer to air filters specifically designed to capture 99.97% of airborne particles that are 0.3 microns. For comparison, a MERV 16 air filter is rated to capture 95% of 0.3 micron particles. HEPA filters are used in many types of room air purifiers and other types of high-efficiency environmental control equipment in order to provide the cleanest, most particle-free air. HEPA filters are popular among homeowners who are prone to allergies as they provide the most effective removal of particles like dust, pet dander, pollen, and other common allergens from the air.

In most cases, furnace filters that are marketed as ‘allergy control’ or ‘allergy reducing’ are simply those filters with MERV ratings of 9 or higher. As the term MERV is not as widely known, many filter manufacturers simplify their packaging and marketing to more clearly state the benefits of the filter in common terms rather than rely solely on the technical specifications. Nevertheless, if you or someone in your family does suffer from seasonal or environmental allergies, purchasing a furnace filter that is rated to have higher efficiency at removing common allergens can definitely go a long way to providing greater comfort in your home and living spaces.

Sure, the term ‘electrostatic’ may sound really scientific, it’s actually a very simple concept that uses the attractive power of static electricity to capture particles from the air. Electrostatic filters are usually made of fine metal mesh in multiple layers. As the air passes through the layers of mesh, the friction between the air molecules and the metal creates a static electric charge. This charge pulls airborne particles towards the metal mesh where they become trapped, leaving the air on the other side of the filter cleaner and free of contaminants. Electrostatic filters are often referred to as washable furnace air filters, as they can be removed from the furnace and washed with water and cleaning solution to remove the built-up dust and accumulation. Once cleaned, they can be reinstalled in the furnace. Because of this, electrostatic furnace filters have a much longer useful life than disposable furnace filters, but are also more expensive.

Simple answer; they’re not. Here in Canada, central air conditioners use the same ductwork and air handling system as the furnace. This means that whether you’re heating your home in the winter or cooling it in the summer, the air moving through your house all uses the same ductwork, and therefore uses the same air filter as well. The temperature of the air has no bearing on the type of filter used in your home HVAC system.  Read our full blog post on summer vs winter furnace filters for more information.

Portable air conditioners or window-mounted air conditioners do not use the ductwork in your home. These units are only designed to control the temperature in individual rooms. Some standalone AC equipment may have a small internal air filter that should be checked when in regular use, as dust can build up over time and hinder the performance and energy efficiency of these portable or window AC units.

No matter how well you clean your home, vacuum the carpet, dust the surfaces, or scrub the floors, there will inevitably be some tiny particles in the air. These can come from many different sources, including outside when doors or windows are open, dust and fibers from carpets and clothing, hair and dander from pets, and the natural process of shedding hair and skin cells as we go about our daily lives. Home improvement projects and renovations also kick up a lot of airborne particulates, as things like replacing carpet, sanding wood, and patching walls all involve the production of tiny particles that can get stirred up in the air. A good quality furnace filter helps keep these airborne particles to a minimum in your home.

Checking the air quality in your home can be done in a couple of simple ways. The first way is to contact a professional air quality testing company that will send a technician to your home to provide a complete analysis. Although this will carry a cost, it is usually the most comprehensive way to get a full report on your home air quality.

Alternatively, you can purchase an air quality monitor for a fairly low cost (about $100 - $200) that you can use to check the air in your home for substances such as carbon monoxide, radon, airborne particles, and VOCs (volatile organic compounds). VOCs refer to a wide range of airborne contaminants that are by-products from the decay of organic material. For example, as mold spores grow and reproduce, they create the typical ‘musty’ smell and foul odor associated with mold growing in a home. These odours exist in the air as VOCs, which can be detected by home air quality testing devices, giving you a strong indication on the types of contaminants that are present in the air.

Depending on the results of your in-home air quality test, you may be wondering if an air purifier would be a good investment. The answer is, ‘it depends’. In the event that you find the air in your home to be of low quality having a high concentration of particles and contaminants, the first thing you’ll likely want to do is perform a thorough cleaning of your whole home. This may include things like steam cleaning the carpets and upholstery, dusting all surfaces, washing all floors, having the air ducts cleaned, and changing the filter in your furnace to one with a higher MERV rating. After this has been done, check the air quality again and see the results. In the event that you are still not satisfied with the results, an air purifier may be advisable.

There are other situations where you may want to invest in an air purifier even if the air quality in your home is quite good. People with heightened sensitivity to airborne allergens may benefit from the increased air filtration of an in-room air purifier, particularly in the room where they sleep. Compact air purifiers can be quite affordable, ranging from about $100 to $800 for the top-end models. In many cases, adding an air purifier to your home can help alleviate the symptoms of allergies, but they are not a substitute for keeping your HVAC system operating at peak efficiency with a high quality filter.

Well, we can definitely recommend one place that has lots of advice and helpful information you can use. Our blog, Filter Facts. We publish new articles regularly that help explain a wide range of home comfort topics, including indoor air quality, energy efficiency, furnace filter buying guides, and so much more.