Furnace Filter Buying Guide

 Trisha Landry

People tend to put lots of time and effort into choosing the right high-efficiency furnace for their homes, and it’s worth also putting a certain level of care into choosing the right furnace filter. Unfortunately, it can be easy for a lot of homeowners to set it and forget it once the unit has been installed.

But regular maintenance is just as important as choosing the right model in the first place. Proper service and maintenance can improve the efficiency and lifespan of your furnace and improve the air quality in your home.

One of those important maintenance tasks is changing the filter, and this guide will go over everything you need to know about the different types of filters, getting the right one for your home, replacing and cleaning filters, and how often you should be replacing them.

Why Furnace Filters Are an Important Part of Your HVAC System

This might seem a little obvious, but furnace filters are important because they filter the air being circulated around your home.

And they’re not just important in winter—your air conditioner also relies on the blower system, filter, and ductwork attached to your furnace. In other words, furnace filters need attention year-round, or at least during the winter and summer months when you’re heating or cooling your home.

There are lots of reasons to keep your furnace filter clean and well-maintained, including improved air quality, increased efficiency, and a longer lifespan for your heating and cooling system.

Air Quality

The air inside and outside your home can be swimming with contaminants that a furnace filter can catch and remove from the air you breathe inside. Some of the most common pollutants include:

• Dust and dust mites
• Mold and fungi
• Viruses and bacteria
• Dander and pet hair
• Smoke and ash
• Volatile organic compounds
• Pollen
• Pesticides and herbicides

Efficiency and Lifespan of Your Furnace and Air Conditioner

Filters also serve another important function: they keep your furnace and air conditioner working optimally. By eliminating dust and dirt from the air, filters also keep these contaminants out of your HVAC system. This means fewer service calls, less maintenance, and a longer life for your heating and cooling systems.

Similarly, a clean filter can maximize the efficiency of your furnace and air conditioner while also improving air flow, and this results in more optimal temperatures throughout the house and lower heating and cooling costs.

Check the Furnace Manual Before Buying Replacement Filters

There are lots of types of filters on the market to choose from, and furnace filters come in a variety of sizes and thicknesses.

The best way to ensure you get a filter that will work with your system is to read through the owner’s manual that came with the furnace. The manual will tell you what size filter to buy and how often to change it. Depending on the make and model of your furnace, the manual might also tell you where the filter goes, what type to use, or how to clean it.

Getting Help When You Don’t Have the Manual

If you don’t have access to the owner’s manual, then you might be able to find a copy online through the manufacturer’s website.

Otherwise, remove the filter from your furnace and check the frame for the dimensions. If you can’t find the dimensions printed on the frame, then measure the length, width, and height (thickness) of the filter, and use those dimensions as a guide when buying your replacements.

Furnace Filter Materials, Styles, and Sizes


Furnace filters can be made of many different materials, including paper, cotton, and polyester, but the most common ones in Canada are flat filters made of fiberglass that’s about 1 inch thick. The style of filter will help to determine the material it’s made of.


Flat filters: These are the standard filters that you’re probably familiar with. They are typically made of spun fiberglass with a thickness of 1 to 2 inches. These are the cheapest and most common filters, but also among the least effective at trapping smaller particles.

Pleated filters: As the name suggests, pleated filters are made from fabric that’s pleated like an accordion. They’re usually made of cotton or polyester instead of fiberglass. These are a little more expensive than flat fiberglass filters, but they’re also better at removing smaller particles from the air.In general, it’s worth the extra cost for a pleated filter because of how much better they perform.

Electrostatic filters: These are filters that have a special electrostatic charge. In the same way that a balloon rubbed against your hair will cling to the wall, so too will larger and smaller particles stick to an electrostatic filter better than a standard flat filter. Electrostatic filters are commonly washable and reusable.

Whole-home air filtration add-ons: There are other air purification devices you can buy for your furnace, such as UV filters, extended media filters, and electronic air filters. These devices are pricier and sometimes require professional installation, but they do have a few benefits compared to the other types of filters.For one thing, whole-home air purifiers don’t need to be changed as often, and they’re much more effective. However, they aren’t always necessary unless someone in your home has respiratory problems or allergies, you live in an area with lots of dust or pollution, or there are other air quality concerns at play.


Furnace filters come in lots of sizes, and the make and model of your heating system will determine which one is right.

Some of the most common sizes are 16 by 20 inches, 16 by 25 inches, and 20 by 25 inches, but they can range anywhere from 10 to 25 inches wide and 12 to 36 inches long.

In terms of depth or height, filters can be anywhere from 1 to 6 inches thick.

Reusable Versus Disposable

The most common furnace filters are disposable, so when it’s time to change the filter, you remove the old one, throw it out, and replace it with a brand new one.

However, another option is reusable filters that are specially designed to be washable. Instead of throwing the filter out every one to three months, you simply remove it from the furnace, clean it, allow it to dry, and put it back.

Like flat fiberglass filters, reusable filters aren’t as great at catching smaller particles compared to pleated filters or whole-home air purifiers, and they’re most effective against larger particles like dust and dirt.

Comparing the Effectiveness of Filters

When you’re shopping for filters, you might wonder how to determine whether or not a filter is worth the money.

Fortunately, there is an objective way to measure how effective a filter is, and that’s with something called MERV.

Minimum efficiency reporting values (MERV) is the calculation used to measure how effective a filter is at removing contaminants that range between 0.3 to 10 microns. The MERV scale runs from 1 to 20, and the higher the number, the better the filter is at eliminating small particles from the air.

Here’s a breakdown of some key MERV measurements:

• MERV 6: Filters dust, lint, and pollen
• MERV 6 to 8: Filters dust and dust mites, lint, pollen, and mold spores
• MERV 6 to 11: Filters dust and dust mites, lint, pollen, mold spores, dander, smog, and large respiratory droplets
• MERV 6 to 13: Filters dust and dust mites, lint, pollen, mold spores, dander, smog, large respiratory droplets, viruses, and bacteria

Anything above MERV 16 is typically only used in specialized settings, such as hospitals, operating rooms, clean rooms, and labs.

TIP! In some cases, thicker filters can cause your furnace and/or connected smart thermostat to detect an airflow issue. You can check with the manufacturer or your furnace manual for their recommendation, or opt for a slightly lower MERV rating.

When to Choose a Higher-MERV Filter for Your HVAC System

For some homes, a standard flat filter will provide sufficient filtration. However, there are many cases when you might want to invest in a filter with a higher MERV rating.
Those instances can include:

• If a member of your household has asthma or other respiratory problems
• You have pets
• Someone in your house smokes
• You regularly use a wood-burning stove
• You live in a dusty climate
• Your home is relatively new and there’s still dust present from construction
• The basement isn’t finished
• The air quality where you live is poor
• Someone in your home has allergies
• There’s a mold problem in your house
• You’ve had issues with rodents or pests
• Your home is particularly dusty or dirty (as in, you live on a dirt road)

Furnace Filter Replacement Frequency Guidelines

How often you have to change your furnace filter will depend largely on the type of filter you have and how thick it is.

Standard flat filters should generally be replaced every one to three months during the heating and cooling seasons. If any of the aforementioned situations apply to your home (such as having pets), then you’ll probably want to change the filter monthly.

Electrostatic filters are similar, and should be washed roughly every month as necessary.

Pleated filters last longer than flat filters, and you should replace them every three to six months. Again, if you have people in your home with allergies or other factors that can negatively impact the air quality in your house, then you should replace the filters every three months.

With both flat and pleated filters, it’s important to note that thickness can also help determine replacement frequency. Filters that are between 3 and 6 inches will last longer than ones that are 1 to 2 inches, and you might only have to replace thicker ones every nine to 12 months.

Signs It’s Time to Change the Filter

It’s good practice to check your filter monthly, even if you don’t change it that often. When you inspect the filter, look for a buildup of dirt and dust on the surface that will look like a greyish or brownish film. When you see that, it’s time to change the filter.

Other signs that indicate it’s time for a replacement include if you start to notice a decrease in airflow, an increase in odours, or an abnormal amount of dust in the house.

How to Change a Furnace Filter

Always start by reading through the manufacturer’s instructions before attempting any furnace maintenance on your own.

The process of changing a filter can vary from brand to brand, but for most makes and models, a simplified version of the process goes like this:

1. Purchase a replacement filter that’s the right size for your furnace
2. Turn off the furnace
3. Open the access panel (you might need a screwdriver)
4. Remove the old filter
5. Insert the new filter, paying attention to the arrows on the frame that indicate the direction of the airflow
6. Replace the access panel
7. Turn the furnace back on

For furnaces with washable filters, follow the same steps to remove the dirty filter. Then, vacuum the filter to remove dust, dirt, and debris. Next, rinse the filter with clean running water, scrubbing gently with a soft brush if necessary. A wet filter can lead to mold or fungi growth, so allow the filter to dry completely before putting it back into the furnace.

Our ElectroDust™ Washable Air Filter

ElectroDust filters provide higher than industry average air quality and are built to higher standards. Our filters are environmentally friendly, allowing you to wash and re-use them over a 10 year lifespan. After just 10 months of using our filters, you will begin to realize savings. Furthermore, because ElectroDust filters are more efficient at capturing dust and foreign particles, you won’t require duct cleaning as often, saving you even more money. Less dusting means a healthier home.

Liquid error (sections/pf-b6039061 line 48): product form must be given a product