Understanding Summer & Winter Furnace Filters

You’ve heard it here before. Changing your furnace filter at regular intervals is absolutely essential in order to keep the air in your home fresh and clean, and to ensure that your HVAC energy bills stay as low as possible. In Canada, this is important as we crank up our furnaces in the bleak cold months of winter and keep our homes cool and comfortable with air conditioning in the summer. However, should you be using a different kind of furnace filter when the outdoor environment changes so dramatically? Here’s what you need to know.

There are a lot of different factors that go into determining how often you should change your furnace filters. For example, having pets like cats and dogs definitely increases the amount of stuff floating around in your air in the form of pet hair and pet dander. Also, if you are going to be taking on a home improvement project, be prepared to experience a lot more dust and dirt in your living spaces while the renovations are underway. In fact, simply having a big family can result in higher levels of airborne particles in your home when compared to homes where there might just be one or two people.

The size of the furnace filter itself also determines how often they should be changed. Thinner filters (1” depth or 2” depth) are usually recommended to be changed every 1-3 months, whereas thicker filters (3”,4”,5”) can last between 6 and 9 months between filter changes. Furthermore, the materials and construction of the filter impact filter life as well. Flat filters made from inexpensive fiberglass sheets generally don’t last as long as pleated furnace filters made from polyester or cotton fiber materials. Filter efficiency also plays a role, as filters that are better at capturing tiny particles from the air will need to be replaced more often than those that are less efficient, but higher efficiency filters will certainly do a better job of keeping your air cleaner.

Read our article about cheap no-name filters vs quality brand name filters to learn why you should spend a little more for a recognized brand name filter.

Now, you might be wondering how regional climates and weather changes could affect the performance of your home HVAC system. Interestingly, even though we tend to think of our interior spaces and the outside world as separate from each other, there’s quite a bit of mixing that goes on between the air inside and the air outside. As seasons change, the air outside can also change significantly. Let’s explore how the different seasons might alter the air inside our living spaces.

How Does the Outdoor Environment Affect Indoor Air Quality?

Canada is a big place. REALLY big. Simply due to the sheer size of our country, the typical weather in one area can be vastly different from other areas. A normal day in Vancouver is certainly not the same kind of weather the residents of Winnipeg will experience. Parts of Canada that are dry and hot in the summer will inevitably be dustier than those spots that are temperate and located nearer to bodies of water.

What does this mean for the air inside your home? Well, every time you open your door or crack your windows, that outdoor air is mixing with your interior spaces and bringing in airborne particles along with it. In the spring and summer, this means dust, pollen, and other common allergens. However, in places where pollen production is not as extreme, opening up windows for fresh air can actually help clear out lingering airborne particles in your home like mold spores or pet dander.

In the fall and winter, the colder air means our homes remain sealed up much more often, and our HVAC systems are set to recirculate nearly constantly. This increases the amount of house dust that accumulates in the furnace filter each day, ultimately shortening its lifespan and resulting in more frequent filter changes.

So, with these drastic changes in climate affecting the type and amount of tiny particles that are in the air inside and outside, should you be looking at a different kind of furnace filter at different times of year? Not exactly, no.

Are there Seasonal-Specific Furnace Filters?

It might seem logical that there would be ‘summer-specific’ or ‘winter-specific’ furnace filters. The reality is that furnace filters treat all airborne particles the same way, regardless of whether it’s hot or cold. They also don’t discriminate between airborne particles if they’re from interior sources like common household dust or exterior sources like pollen. In a nutshell, no, there are not furnace filter types that are designed specifically for summer or for winter.

What DOES matter as the seasons change and the outside climate moves from hot to cold and back again, is how often you will want to change your filter to ensure that your inside air stays clean and free of airborne particles of all types. Plus, if you or someone in your home experiences allergies or has some other type of respiratory sensitivity, the filter efficiency rating is another important consideration when buying replacement furnace filters, regardless of what time of year it might be.

Choosing the Best Furnace Filter for Every Season

The number one thing you need to know when looking for a replacement furnace filter is what size you’ll need. There are numerous different furnace filter sizes for all the different makes and models of home furnaces that are popular in Canada, so this is the first thing you’ll need to be sure of before you start shopping. Fortunately, it’s pretty easy to find the right filter size, especially with our Guide to Furnace Filter Sizes to help you out! If you’re not sure what size of filter your furnace takes, you should definitely check that guide out for all the details, but here’s the basics of what you need to know.

• Start by checking the current furnace filter that’s installed in your HVAC system. On the frame of the filter, you should see a size indicator that lists the length, width, and depth/thickness of the filter in inches. It should look something like “20x25x4”. This means the filter is 20” long, 25” wide, and 4” thick.
• Can’t find the size marked on the filter? You can check the furnace owner’s manual for the size specifications, or download a digital copy from the manufacturer’s website if you don’t have the manual handy.
• You can also grab a tape measure and jot down the three different dimensions of the current filter. Just remember that you’ll probably need to round up to the nearest inch to find the standard size. For example, a 20x25x4 filter will probably have actual tight measurements of 19 ¾”x24 ¾” x 3 ¾”.

Once you’ve got the size nailed down, you should take a moment to consider what level of filtration efficiency you might need. Filter efficiency is indicated with a rating on the MERV scale. This acronym stands for Minimum Efficiency Reporting Value (MERV), and specifies how efficient the filter is at capturing tiny airborne particles between 10 microns and 0.3 microns in size.

For the whole story, you can refer to our Guide to Furnace Filter MERV Ratings, but there’s a few key points you really should know.

Most furnace filters start with a minimum efficiency rating of 8, which does an adequate job of capturing the majority of airborne particles and keeping your home furnace operating efficiently. For better filtration and cleaner air, particularly in drier and dustier climates, a higher MERV rating of 10 or more might be a wise choice. This level of filtration is needed to provide greater control of airborne allergens such as dust, pollen, mold spores, pet dander, and other common respiratory irritants.

During peak allergy seasons, you’re definitely going to want to have a filter in your furnace that’s more capable of containing those annoying allergens so your whole family can breathe easier. This is also true during the coldest months of the year when you’ve got all the windows closed up and the HVAC system is constantly moving air to keep your living spaces comfortable.

The top-end rating for most home furnaces is generally MERV 16, as anything higher than that could put too much restriction on the airflow through your ducts. This can result in lowered energy efficiency of your furnace and decreased filtration performance. If you desire the cleanest air possible in your home, it may be a good idea to invest in a standalone air purifier. These units feature filtration efficiency even higher than MERV 16, with many of them reaching HEPA (High Efficiency Particulate Air) filtration levels.

The Last Word on Summer and Winter Furnace Filters

At the end of the day, do you need to worry about hunting down a summer- or winter-specific furnace filter? Nope. You just need to get a good quality filter that’s the right size, with a high efficiency rating to keep the air in your home clean and free of airborne particles all year long, and change it regularly for maximum performance from your HVAC system. To find out exactly how often you should change your furnace filter, we’ve got a comprehensive Guide to Furnace Filter Change Frequency. Be sure to give it a read through to find out what other factors can impact how often you should change your furnace filter for the cleanest possible air in your home.

The seasons will inevitably change, but you’ll always need clean air in your home. Give your furnace the help it needs to do its job well with a high-efficiency top-quality furnace filter, and make sure to change it regularly. 

Have any other questions? Our filter FAQ page might have the answer you’re looking for. If not, contact us and we’ll be happy to help!