Shop Furnace and AC Filters Online

Trusted in filtration since 2006, we've replaced and sold over a million. That’s billions of particles removed from indoor air. Trust your air to us. RTF has been in business for 16+ years and is a preferred online retailer for leading brands like Exact Filters®, AAF FlandersEZ-Flow, and NaturalAire Furnace and AC Filters. We sell filters by the case or individual filters with our subscription program.

HVAC, Furnace, AC Filters for Residential and Commercial

What’s your need? Commercial? Residential? Industrial? HEPA? We have you covered! At, you’ll find the perfect HVAC, Furnace and AC filters online for your system. Our stock features leading manufacturers. 

Buying furnace, HVAC, and AC filters online at is easy, convenient, and saves you time and money. No high-pressure sales. No time-consuming service appointments. No searching for weeks or months for your filter size. Just friendly, knowledgeable filter experts dedicated to helping you select the right filters for your system. 

With thousands of sizes to choose from, you’ll never have to search for your filter again. You can even buy custom furnace and AC filters online. We’ll send you perfect fit filters for your HVAC system. We deliver filters to you for free, too! Whether you live here with us in the Pacific Northwest, or you’re in Texas, Chicago, New York, Los Angeles, or Florida, we deliver for free anywhere in the entire contiguous United States – even oversized or special order filters. 

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Exact Filters® - Get the Perfect Fit!

Finding the perfect fit filter isn't easy when most manufacturers only offer a handful of standard sizes - rounded to nominal dimensions. Exact Filters® are high quality perfect fit HVAC filters made with only a 1/8" +/- manufacturing tolerance. Exact Filters® are made to your exact size ensuring no dirty air is bypassing your system. is the exclusive retail partner of Exact Filters®.

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MERV Rating

MERV Rating Explained

Minimum Efficiency Reporting Value (MERV) is a filter industry standard system that rates the overall effectiveness of air filters.

Some of the common particles that filters are tested for include pollen, dust mites, textile and carpet fibers, mold spores, dust, pet dander, bacteria and tobacco smoke.

MERV 8 ratingReduces up to 75% of large airborne particles including: Dust and Lint, Dust Mite Debris, Pollen, Pet Dander, Mold Spores, Bacteria and Virus Carriers.

MERV 10 ratingReduces up to 85% of airborne particles as small as 1 micron including: Dust and Lint, Dust Mite Debris, Pollen, Pet Dander, Mold Spores, Bacteria, Virus Carriers, as well as Most Smoke and Smog.

MERV 13 ratingReduces up to 95% of airborne particles including: Dust and Lint, Dust Mite Debris, Pollen, Pet Dander, Mold Spores, Bacteria, Microscopic Allergens, Virus Carriers, Most Smoke, Smog, Oil Smoke, as well as Lead Dust

MERV Ratings

Benefits of Clean Furnace, AC and HVAC Filters

A furnace, AC and HVAC filter pulls unwanted particles from your indoor air. Such as mold spores, pet dander, household dust, smoke, pollen, dust mites and smog. Using a filter in your furnace is an easy way to reduce the cost of energy you use, a dirty filter will force your system to work harder to push air through the filter, while a clean one will allow the air travel more freely. The filter also keeps the coils and the heat exchangers in your system clean. Having dirty filters will make your system work harder and restricts the air from moving through. This could lead to maintenance issues and the harder your system works the more energy it uses which in turn costs you more money.

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How Often to Replace a Furnace or AC Filter?

Recommendations vary based on a number of factors: the type of furnace filter that you use, how many pets you have, whether anyone in your home has allergies, etc. If you use disposable fiberglass panel or electrostatic panel filters, you should change them anywhere from once a month to once every three months. Pleated filters generally last 3 months. Filters are relatively inexpensive and easy to change, so there is little reason to wait. If you don't change or clean your filter often enough the filter can get clogged with dust and other airborne particles, forcing your furnace to work harder to maintain airflow. This will reduce your furnace's efficiency and can cause damage.

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Types of HVAC, AC and Furnace Filters

The filter is a very important piece of maintenance for your home or business. Learn about the different types of HVAC, AC and Furnace filters available to make the best choice for your home or business.


Pleated filters are most commonly made from either polyester or cotton paper. Most of the pleated filters we sell are made with 100% synthetic non-woven, proprietary media, with low initial resistance and high dust-holding capacity which combine to provide an extended life cycle and energy efficient performance. Pleated filters are the most popular option for removing small particles and improving air quality. Pleated filters have MERV ratings that range from MERV 8MERV 10MERV 11 and MERV 13. They should be replaced every 90 days on average.


A cheaper option for an HVAC filter would be to go with one that is fiberglass. A basic fiberglass filter is disposable, are easy to install, and can give your systems protection that it needs. They will help with dust and larger particles but the primary function is to protect your system. Fiberglass filters are not restrictive so your system will not have to work hard to move air through the filter. On average they should be replaced every 30 days. Here at RTF, you can get fiberglass filters in a 12-pack, so you can always have a filter ready to go. 


If you don’t want to keep replacing your HVAC filter, then you could go with one that is washable. While a washable filter may cost more than a regular filter, you can save money over time. Keep up with the washable filter’s maintenance by regularly cleaning it properly to avoid particle buildup. One issue with washable filters is when customers clean them. You always want to be sure they are cleaned and dried properly so your are not degrading air quality when put back into your system.

Exact Filters®

One of the hardest parts about shopping for an HVAC filter is getting one that is the perfect size for your unit. At RTF, you can find Exact Filters that will fit perfectly in whatever system you own. With Exact Filters, you can go with a MERV 8 filter, MERV 11, or highly rated MERV 13 filter. Don't let anything get past your filter - Exact Filters for when standard filters don't make the cut.

Custom Filters

At, we offer custom furnace filters and custom AC filters, so you can install a filter that fits your HVAC unit exactly. A well-fit air filter not only improves air quality in your home or business, but it can also extend the life of your equipment. If standard sizes don’t work for your needs, then our custom size HVAC filters are the ideal solution. With our custom furnace filters, we enforce high standards, top craftsmanship, and consistent quality. We will have the filters made to the exact size you specify, ensuring they fit perfectly into your system. A high-quality perfect fir filter can keep you and your family breathing cleaner, healthier indoor air.

Grille Cut

Grille cut filters are typically difficult to find because they come in odd sizes. However, RTF offers Grille filters that come in dimensions that will be suitable for your unit to ensure quality air in your home or business. It’s also worth noting that the measurement of the grille cut filter will be smaller than its actual size with some odd dimensions. For example our most common grille filter listed as 23 x 20 x 1 has an actual size of 22-1/8 x 19-3/8 x 3/4.


A HEPA filter, also known as a high-efficiency particulate absorbing filter, meets predetermined levels of performance efficiency. According to the United States Department of Energy, this means that a HEPA filter must remove 99.97% of particles with diameters equal to 0.3 micrometers. Therefore, these filters can efficiently and effectively trap micro pollutants like dirt, dust, pollen, moisture, bacteria, and viruses. HEPA filters are most often used in spaces that require highly effective contamination control, such as laboratories, hospitals, manufacturing plants, and nuclear facilities.

Common Air Filter Terms

Collection of common terms you may come across while shopping for replacement filters for your home or business.

ASHREA: American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is an international membership organization founded to advance the arts and sciences of heating, ventilation, air conditioning, refrigeration and related issues. is an ASHRAE member.

MERV: Stands for the Minimum Efficiency Reporting Value, and is a measure of a filter's worst-case efficiency performance. The higher the MERV rating, the more efficient the filter. MERV is an industry standard rating, so it can be used to compare filters made by different companies.

HVAC: The acronym HVAC commonly refers to Heating, Ventilating and Air Conditioning. Some parts of the country may only have air conditioning while other parts of the country may have furnaces with or without air conditioning. This term is can be applied to air comfort systems for all situations.

Micron: A micron is a measure of length: "1 micron equals 1 millionth of a meter". A particle that is 10 microns or less in size is not visible to the naked human eye.

HEPA: The Letters in the word HEPA stand for High Efficiency Particulate Arrestance.

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The Difference Between Exact and Undercut Furnace Filters

We get the question what is the difference between an exact and undercut furnace filter often. Usually when customers are having a hard time locating a specific furnace filter size from a local store. The industry as a whole regardless of manufacturer undercuts standard size filters. An example is the PREPleat MERV 8 rated filter by AAF Flanders in the size of 16x20x1, one of our most popular filters. This filter has an actual size of 16-1/2x19-1/2x3/4. On the filter you will find the nominal size printed of 16x20x1 but the actual measurements are slightly smaller, this is an "undercut" standard size furnace filter.

This can create some confusion typically when a customer needs an odd size filter. Standard sizes are always undercut where custom filters can be "exact" or "undercut". This is the main reason we always recommend double checking your filter measurements. Depending on where your HVAC, AC or Furnace filters were purchased the size printed on your filter could listed as the nominal (rounded) size but the true size might be slightly smaller. This can create an issue if your custom/odd size filters don't fit.

We prefer to submit all orders as "exact" if you are using an odd/custom size filter. This way in the future when it's time to order replacement furnace filters you won't question the size of your filters, or end up with a box of filters the wrong size.

If you have any questions about custom furnace filters please reach out to customer service to help ensure you get the perfect fit for your HVAC system.

Measuring your furnace filter

How to Measure Your Furnace or AC Filter

Choosing the correctly sized air filter is important in order to keep air clean in your home. An improperly sized filter may have limited performance. Determining the proper air filter size can be confusing, since filter packages generally display two sets of dimensions. It is important to understand that these dimension sets are the nominal and actual dimensions of the filter, and differences between the two.

Basic Measuring Tips

Use a steel measuring tape. Measure your old filter to the nearest 1/8" of an inch, if the size is on a 1/16" mark, then round down to the next 1/8".

Nominal Size:

The dimensions listed on the side of air filter frames and printed largest on air filter packaging are normally the nominal size dimensions. These measurements indicate the length, height, and depth (thickness) of the air filter, rounded up to the nearest inch. An example of nominal dimensions would be 16” x 24” x 1”.

Actual Size:

These are the exact dimensions of your air filter when measuring length, width, and depth (thickness). On air filter packaging this number is typically listed under or to the side of the nominal size, and is normally in a smaller font size. Most actual size measurements include fractions. An example of actual size dimensions would be: 15 ½” x 19 ¾” x ¾”.

How to measure your air filter:

To measure your air filter, use a tape measure to determine the width, height, and depth. If a pre-existing filter is not available, inspect the unit for a listed size. If easily accessible, measure the air filter housing slot, or refer to your furnace instructions manual for more information.

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Locating your HVAC, Furnace and AC Filter

In many cases if you have never located your heating systems filter it can be a challenge to find it. All systems are different so we will do our very best to point you in the right direction. Typically your filter is going to be somewhere near the blower (fan), this is because one of the main purposes of a filter is to protect the blower (fan) from damage. This applies to all different types of furnaces, including gas furnaces, oil furnaces, electric furnaces, as well as air conditioners.

Step 1

Make sure the fan is not running, you can do this by setting your thermostat to the off position and turn off power completely to the unit.

Step 2

Locate the service panel (main cover), usually on the furnace's front or side. The front of most systems will have a label that gives details on removing the cover/panel. In most cases you will not need tools to remove will just have to pull up on the handle and it will pop out.

Step 3 

Now that you have removed the panel locate the filter. You should be able to see the frame of the filter sitting horizontally or vertically near the blower (fan). If you find the filter slide it out and take note of the size.

If you couldn't locate your filter by following the steps listed above work you way backwards from the return duct this is the one that brings air into the system, remember since the filters main purpose is to protect your system and keep it running efficiently it is going to be somewhere before the blower (fan). In some situations there may be no furnace filter present. It may have been removed instead of replaced, or it may have never been installed in the first place. In this case replacing the filter will be a greater task. If you can locate what looks to be where the filter would go you will need to take measurements to be sure you order the correct size. If you can't locate the location of the filter we suggest you consult a local reputable HVAC company to do an inspection of your system and inform you of the size of filter you need and where it goes.

How to locate your furnace filter

Wholesale HVAC Filters | Furnace and AC Filtration (RTF) is a retailer with over 16 years in online business and over 45 years in combined experience in the Furnace, AC and HVAC filter industry. If you purchase filters in bulk you might be a good candidate for a wholesale account that gives you special access to our commercial pricing website. We feature HVAC filtration from industry best manufacturers like AAF Flanders and we are the exclusive retailer/wholesaler of Exact Filters®, the perfect fit for your customers and systems.

Suitable for many types of businesses not only retailers; hardware stores, commercial properties, school districts, hospitality, HVAC contractors and more. You don't have to be a retailer to gain access to our wholesale website to place orders and manage your filtration needs. Our wholesale site will allow you to make purchases at your discounted pricing for both end users and retailers.

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