How To Choose Furnace Filter?

Your furnace works hard to keep you warm when it’s cold outside, and to make sure it keeps working hard, and efficiently, you need to keep your furnace filter clean. The filter pulls allergens and other airborne debris from the air so that you don’t have to breathe it in, but when that filter gets filled with particulates and is dirty, the reduced airflow can tax your system.

Here’s how to choose a furnace filter:

  1. Find out the size filter your system requires.
  2. Decide how much money you want to spend.
  3. Assess how much filtration you need.
  4. Understand Minimum Efficiency Reporting Values, or MERV.
  5. Buy, install, and regularly change your filter.

The furnace filter serves as a key component to keeping your home a comfortable place to be, but if it’s not maintained, you can run into some problems. This article will show you what you need to know about choosing the right furnace filter, how to install it, and how to regularly maintain it. Let’s get started.

1. Find Out the Size Filter Your System Requires

Three standard furnace filter sizes are 16″ x 20″, 20″ x 25″, and 16″ x 25″ (40.64 x 50.8 cm, 50.8 cm x 63.5 cm, 40.64 x 63.5 cm). There are other sizes, though, so don’t just assume you know which one you need. Be sure to measure the intake vent where the filter sits, consult your furnace’s user manual, or check with the manufacturer. 

If the filter you end up with is too big, you won’t be able to install it without bending, damaging, or otherwise compromising it, but if it’s too small, it won’t do its job. 

A too-small filter will leave gaps on the sides. Since airflow will always take the path of least resistance, gaps mean most of the air your furnace takes in will avoid going through the filter at all, but rather around it. All those allergens, dust mites, and other things you don’t want floating around will skip the filter and come pouring out of the vents in your home.

If your filter is too small, you may as well not have any filter installed. And if you’re not sure if your filter is too small, here are some clues:

  • If you can see visible gaps between the filter’s edges and the edge of the vent it sits in, that’s a pretty good clue.
  • Filters that are too small may rattle in place, so if you’ve put in a new one and suddenly start hearing a new rattling sound, check the filter size first.
  • When you put in a new one but then soon after that notice an increase in dust in your home, you’ve probably put in too small a filter.

Check your sizes!

Read: How Often To Change Furnace Filter?

2. Decide How Much Money You Want To Spend

As with so many things in life, you’ve got options when it comes to buying a filter— you can spend a lot of money or just a little. What you need and want from your filter will determine how much you should spend.

Filter material choices include fiberglass, polyester, paper, and even cotton. On the lower end of the price spectrum are the disposable pleated air filters like these from Aerostar (available through 

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You’ll need to change out filters like these every three months or so.

And before you decide that because it’s less expensive, it must be a worse filter than a pricier one, think about this next point. The pleats in the filter mean more surface area inside the filter. By adding the accordion-style folding, manufacturers can put in more filtering capacity since there are a lot more places for the dirt and dust to get stored.

Also, since they’re disposable, you just toss them and replace them when the filter’s full.

Higher-cost filters can be reusable, and some don’t have pleats in them. That doesn’t mean they don’t filter as well, but it does mean you’ll need to change them more frequently. Reusable filters usually just need a good rinsing when they’re dirty. 

Spray them with water to clean off all the dirt they’ve collected, let them air dry, and then reinstall them.

Filter Everything makes this reusable Washable Aluminum Air Filter, and there are also filters like the Aqua-Flo Washable Air Filter Pad (both are available on This polyester filter is a cut-to-fit material, so if your system requires an unusual filter size, something like this would be the way to go.

Reusable filters certainly constitute a greener solution, but again, since they require more frequent maintenance, if you use them, you’ll have to keep up with them. Without proper care, dirty filters can end up harming your HVAC system.

Read: Does HVAC Filter Direction Matter?

3. Assess How Much Filtration You Need

Most homes and HVAC systems work great with a regular, disposable air filter. However, harder-working filters that snag more and finer particles from the air might fit your needs better if you need more-than-average filtration in your home. 

There is a demonstrated link between higher-quality air filters and a lower frequency of asthma attacks, so if you or a family member deals with this breathing issue, the right filter can do great things for you. The same goes for allergy sufferers, as some filters work specifically to remove pollen and other allergens.

Those are generally smaller than dust particles, so a filter like Filtrete’s Micro Allergen Defense (available on filter can help cut down on those things in your home.

Is someone in your home a smoker? A HEPA-rated filter can help knock down some of the lingering smoke odor. Depending on how much smoking happens in your home, you might even be able to eliminate the smell altogether.

Read: Do I Need Filters In My Return Vents?

4. Understand Minimum Efficiency Reporting Values, or MERV

Filters get evaluated and marketed based on their MERV score. The Minimum Efficiency Reporting Values (MERVs) describe how well a filter can catch and remove pollutants, allergens, and other particles. 

The higher a filter’s MERV rating, the better it filters out the smaller particles in the air flowing through your system. A MERV rating higher than 6 tells you that the filter in question can remove up to 50% of particulates between 0.3 and 10 microns in diameter. A micron is about one 25,000th of an inch (one 1,000,000th of a meter). So, you know, pretty small.

People with higher sensitivities to allergens and pollution or with respiratory issues can benefit greatly from using a filter with a high MERV value.

Read: Does Air Handler Have Filter?

5. Buy, Install, and Regularly Change Your Filter

Whether you buy your filters one at a time or in packs so you have them ready at hand when you need them, be sure you install them correctly. As I mentioned, an improper fit or installation can render the filter useless, and failure to change filters out when they’re dirty can cause issues with your HVAC system.

When your system has to wheeze while trying to suck air in through a dirty filter, the extra work it has to do adds up and can result in some mechanical failures. You may also experience a freeze-up of the system, reduced efficiency (which costs you money when you pay the utility bills), or the lack of airflow from your ducts.

Beyond that, too much dust in your system, such as when your filter lets lots of dust into the system, can gum up the mechanical workings of your HVAC system. Those things have lots of moving parts. 

Introducing foreign objects— even tiny pieces of dust— can cause real damage.

Read: Why Does My Central Air Have Two Filters?

Key Takeaways

Air filters make the air in our homes more comfortable and safer to breathe, and they help keep our HVAC systems working correctly. When you need a filter, know the size you need, and have an idea of how much filtration you require.

Once you have the new filter in place, don’t just set it and forget it. If yours is a disposable filter, keep up with the schedule and change it regularly. If you’ve installed a reusable one, be sure to keep it clean, again paying attention to a maintenance schedule. HVAC repairs can get costly pretty quickly.