The timely replacement of your furnace filter is a lot easier when you know what air filter size you need. AC filters are available in many different sizes, so it can be overwhelming if you’re not sure what size filter you need.
We don’t recommend relying on what you think is the right size and we don’t want you to feel uncertain when it comes to ordering your HVAC filter. At FiltersFast.com, our goal is to equip you with the knowledge you need to make the right decisions.
What is a standard air filter size?
HVAC air filters can be difficult to understand initially. The most used size is 20” x 20” x 1”. However, it’s important to remember that this is only one of many dimensions.
Why Sizes Vary
The size of HVAC filters can differ based on the requirements of your system. Some of these factors are:
System Design
Different HVAC systems are built to support a particular airflow and filtration need.
Home Layout
If you have a large home, it may require more or larger filters to support proper air circulation.
Need a replacement air filter for your HVAC system?
Can I use the wrong size air filter?
If an air filter is too big, you will have to return it. DO NOT cut it to fit. Cutting a filter to fit can create air gaps and contaminants can pass through into your air. Here’s why sticking to the right size is essential.
Efficency Loss
Regardless of if your misfit air is larger or smaller, it can result in poor air flow. This will cause your HVAC system to work harder and result in an efficiency loss.
Higher Energy Bills
Because the system has to work harder, it will require more energy to facilitate this. This will unfortunately increase your energy bills.
System Damage Risk
Asking this much from your HVAC system for an extended period of time will eventually cause it to fail. This will require repair, which can be expensive.
Reduced Air Quality
A improperly measured filter will not properly trap contaminants, negatively affecting your air quality.
The longer you wait to change your old, clogged filter, the more restricted airflow can become. When airflow is restricted two things can happen:
- Your energy bill will start increasing because hot or cold air can become trapped behind a wall of particles.
- Your HVAC system will have to run for longer because hot and cold air is not circulating properly.
- Your indoor air quality will become poor because fresh, clean air is unable to flow into your home.
If an air filter is too small, this will create air gaps and contaminants will bypass the filter material.
How do you figure out the right air filter dimensions you need?
Here are three easy ways to determine the right size air filter you need:
1) Check your current air filter!
In most cases, the air filter dimensions will be printed on the side of the filter.
2) Measure it!
Air filter dimensions are written as length, width, and depth (for example: 18x20x1). You can use a tape measure to get the size of your existing filter You should have three numbers written in inches. This is what is called “actual dimensions”.
If you measure your filter, you may find that these measurements are not round numbers.
When shopping for air filters, you will see the words “nominal size” and “actual size” together. The reason for this is that many air filters are not cut to an exact size. Normally, we see air filters being around 1/8″ to 1/4″ smaller than advertised. This guarantees that if your air conditioning system is designed for 18x20x1 if that number is off by even a little bit the filter will still fit.
Air filters come in tons of standard sizes, but if you are having trouble finding the size that you need, FiltersFast.com can make custom furnace filters for you!
3) Check your HVAC owners manual!
If all else fails, refer to your air conditioning system product manual or contact the manufacturer directly with your system model number. They can help you figure out the exact filter specification for your unit.
If you buy your air filters from FiltersFast.com, your filter information is stored in your customer profile, so all you have to do is reorder!
How often should I change my air filter?
Now that you have an idea of the right size for your filter, you may wonder how often you should replace it. Keeping your home’s air clean is essential to health and wellness. Although there are several steps you can take to accomplish this, the simplest and most important one is to change your filter regularly. For most people, it’s recommended to replace your filter every three months, but other factors can affect this.
Pets
If your home has furry friends tumbling about, there will be more pet hair in the air, which will, in turn, affect the filter/HVAC system. To keep your filter fresh and system safe, you may need to change it every 30 to 60 days.
Allergies
If you or a loved one suffers from allergies or asthma, more frequent changes from 20 to 45 days will help manage the symptoms.
Household Size and Usage
If you have a larger home or multiple residents, your filter change frequency may need to be increased to accommodate the increased dust and usage.
Seasonal
During certain seasons, we make our HVAC systems work harder. When summer and winter are in effect, you’ll want to take note and be prepared to replace the filter to manage the increased workload.
Benefits of Regular Replacement
The most obvious benefit of replacing your filter is fresh air during daily home activities. There are some others as well, such as:
Improves Energy Efficiency
Clean filters guard your HVAC system from dust particles, which helps it run efficiently and lowers energy bills.
Extends HVAC Lifespan
Consistent maintenance will ensure your system never strains to accomplish its goals, extending its lifespan.
By being intentional about maintenance, you can ensure a healthier and more comfortable living environment. However, it may be tough to maintain this consistently. You can try certain tricks like putting reminder notes on the fridge or setting up a notification on your phone. But by using an auto-delivery program, like our Home Filter Club, you won’t have to worry or stress at all.
By choosing to Save with a Subscription at checkout, you’ll receive your filters on time. This will ensure your home is full of fresh air and your HVAC is protected from harm.
For more information about air filters, check out the following articles:
- 4 SURPRISING Reasons Your Air Filters Get Dirty Quickly
- Using AC Air Filters To Keep Cool
- 5 Tips to Make Your Air Filter Change Smoother
- Which Way Does the AC Air Filter Go?!
Brandon says
Hello Patrick, thanks for reaching out to us! Here is an illustration!
As you can see the length is considered the longest part of the air filter, whereas the width is the shortest part. Hope that helps! If you have any other questions, please feel free to contact us at [email protected]!
Patrick Sweeney says
Is there an illustration that shows what is considered the width & length of the air filter?
Brandon says
Osama, thanks for reaching out to us! The nominal size for your filter will be the actual size that you provided, then rounded up. The third element is the depth of the filter, and that is dependent on your needs. Most HVAC systems standardized at around 1 – 2in. If you want to be absolutely sure you get the correct filter size for your system, you can order custom filters with us here. https://www.filtersfast.com/P-Filters-Fast-Custom-Air-Filters.asp We’ll take the actual size that you provide and ensure it fits for your needs. Hope that helps! Take care!
Osama says
WAPM364A
https://www.kingersons.com/images/ProductImage/Productpdfs/58a705315a521c34130000d8/Specification%20Sheet.pdf
The filter size is listed as
16−3/8 x 21−1/2
(416 x 546)
What is the recommended filter size in this case?
Brandon says
Hello Nora, thanks for your comment. It would probably be best to get more information about your unit. We’d recommend contacting the manufacturer and have your system model number at the ready. If you have any more questions or need additional help, please contact us at [email protected].
Nora says
Hi, I have an Emerson E250451, the previous tenant shoved a giant filter that doesn’t fit in there and there’s no manual, not even online. Please help! Where do I measure? The back of the unit? Would it be slightly larger than the unit. The previous tenant also lost the grate/cover. Thanks!
Katie says
Herb,
Thank you for reaching out to us. We are sorry to say we do not show a reference to that model. We would recommend removing the existing filter and measuring the filter to confirm the actual dimensions.
Katie says
Herb,
Thank you for reaching out to us. We are sorry to say we do not show a reference to that model. We would recommend removing the existing filter and measuring the filter to confirm the actual dimensions.
Herb Canada says
HI, my heating unit is FG7SA-045C-23A
My manual does not say what filter to out in, can you please assist?
Katie says
Michael,
Thank you for reaching out to us. We are sorry to say we do not show a reference to that number. We recommend removing the existing filter and confirming the printed part number. If that is not available we could also use the actual dimensions of the filter.
Michael Kozdron says
I have a trane Xb tue1c100a481ab there is nothing inside to hold filter in place using 20×24 but not sure if it correct
Katie says
Karen,
Thank you for reaching out to us. Not all 16x20x1 (nominal size) filters are made equal. If you physically measure the filters you will find that they are made to a different (actual size). This varies by manufacturer. If you move down to the 15″ you may be allowing too much room where air can go around the filter. If you cannot locate filters that are made to the actual size that you need we would recommend ordering custom-made filters. You may view our custom order page here: https://www.filtersfast.com/P-Filters-Fast-Custom-Air-Filters.asp.
Karen A. Lyons says
hello My air handler calls for a 16x20x1 I struggle to get it in and it bends, I worried its not flat in the unit. Is it better to down size to a 15x20x1 and have the filter go in easier and flatter?
thank you for your help.
Karen
Katie says
Lynda,
Thank you for reaching out to us. We would not recommend that you use a filter that is smaller or larger than the filter size you need. Installing a smaller filter will allow unwanted contaminants to pass through and get into your home’s air and HVAC system. Did you order your air filter from us? If so, we have 365 day returns and are happy to assist you in getting the right size filter you need. Please email us at [email protected] and one of our associates will be more than happy to help you with your return and new order.
Please feel free to reach out us if you have any additional questions.
Lynda LuAnn Booker says
Hello! Can you please help?
I accidently purchased a 20x24x1 filter instead of a 20x25x1 . Can I safely use the smaller 20x24x1 without a problem?
Thanks!
LuAnn
Katie says
Karl,
Thank you for reaching out to us. Yes, the filters are similar. The filter will simply be rotated to fit. It is common practice for the smaller dimension to be listed first (20×23 versus 23×20). Please ensure you are ordering the correct actual size. We do not see that as a standard dimension. We believe you may be seeking our custom order page (link below). Note, the filters will be made to the actual Height x Width provided. Thank you for your consideration. Have a great rest of the week!
https://www.filtersfast.com/P-Filters-Fast-Custom-Air-Filters.asp
karl says
Hello. I currently have a 23x20x1 filter in my furnace. Can I use a 20x23x1 they are the dimensionally same size?
Katie says
Rebecca,
We completely understand that figuring out what size air filter you need can be tricky. Do you have an existing air filter? Many brands print the size on edge of the filter. You can also measure it yourself to get a more accurate measurement. Here’s a helpful video about measuring for your air filter: https://www.youtube.com/watch?v=UemPVuQF4ZY
We also have another blog about how to measure your for your air filter too if you’d like to check it out: https://www.filtersfast.com/blog/index.php/2019/05/how-to-measure-your-air-filter/
If you have any questions or need any additional help, we’re happy to assist you!
Rebecca Lauer says
I can’t figure it out
Katie says
James,
If the current filter fits in your return, that should be the right size. We carry a variety of different size filters and different brands. If you do not see your filter size listed, we can make one custom for you. Please visit this link to order: https://www.filtersfast.com/Air-Filters-Purifiers-cat.asp
If you have any other questions or need assistance ordering, please feel free to reach out to us by calling 866-438-3458 or email us at [email protected].
james says
I am buy a filter to replace the old one. For the ac we get last year & filter size said 16x25x1 . Please help me out. Thank you
Katie says
Nancy,
Thank you for reaching out to us. We are sorry to say we do not show a reference to your air handler. The 16.25 x 21 x 1 may be a nominal size. We would recommend removing the current filter. Measure the filter to confirm the actual dimensions, and order based on these dimensions. If you have trouble sourcing these we do offer custom sizes (filters made-to-order) on our website. https://www.filtersfast.com/P-Filters-Fast-Custom-Air-Filters.asp
Nancy says
I have a Rheem RBHP-17J06SH1 Air handler. The repair man said I need a 16.25 x 21 x 1 MERV 8 Filter. I can’t seem to find that exact size. I see 16.25 x 21.5 x 1. Would that be too big?
Katie says
Ron,
Thank you for reaching out to us. The unit will pull the filter towards the ductwork while it is in operation. The spacing will likely cause the filter to shift back and forth as the units cycles on and off. Another thing to consider would be the decreased capacity of a more narrow filter. This will require it to be changed more often. Where possible, we would recommend purchasing a filter that is true to the intended size. If you provide the actual size of the filter needed we will be happy to research that for you.
ron says
The standard filter seems to be about one inch too narrow. I buildt a piece to fit and tape securely. is that adequate
Katie says
Mona,
Thank you for reaching out to us. Manufacturers make their filters to different actual dimensions. A filter in that size is normally referred to as a 16x25x1. We would recommend physically measuring the old filter and the space for it in your unit to confirm a range of compatible actual dimensions. Our filters have a height of 0.75″. This is fairly common although some filters measure a full 1″ in height.
Mona says
I have a carrier furnace and the filter that I buy is 25 by one by 16. It’s very difficult to get it into the space. The width is fine the length is fine but the height seems to be the problem. What do I do
Katie says
Hi Glen,
Thank you for reaching out to us. We do reference a filter close (15-3/8″ x 21-7/8″ x 5-1/4″) to those actual dimensions. You may search for part number DTLP102-1620 or use this link: https://www.filtersfast.com/p-Totaline-DTLP102-1620-16×20-MERV-11-Filter.asp
Please confirm the specifications before ordering.
Glen Whiting says
I am looking for an electrostatic furnace filter. The filter in my furnace is 16 X 20 X 5. The actual measurements are: 15 2/8 X 21 7/8 X 5 1/4. I do not need the 5 1/4 depth because I can modify the filter opening to accomodate a thinner filter.
Kory says
Hello Jordan,
What is the Carrier model number?
If you don’t have that, you will need to actually measure the filter that is currently inserted to get exact dimensions. You may need a custom size filter if you are unable to find the current size you listed above, which we do offer.
Thank you,
Jordan jacobs says
I have a permanent filter in my furnace, came w carrier furnace. I have to wash every month. I want a regular everyday filter I can change every month , and throw out and put new one in. The size I written on filter, 14 5/8 x 21 5/8 x1. Can you please convert that, I can’t find any that size. What size do I actually need!!! Thank you please help!!!!
Kory says
Hello Ruby,
Unfortunately, we do not sell washable A/C unit filters.
Thank you,
Ruby K Moore says
My filter 20X30X1 I have Asthma and COPD and Alergies. I wamt a filter that I can wash with a hose and replace.
Kory says
Hello Andy,
Every filter has an “actual” size vs a “nominal” size. The nominal size is the 21x22x1 that you mentioned but you will need to actually measure the filter that is currently inserted to find the actual size that it is. You will find that there may be anywhere from a 1/4-3/4inch difference between the numbers. We have all actual sizes listed on our website for easy reference.
Thank you,
andy says
Hello im trying to find an ac filter 21x22x1 but all the ones i find say that the actual sie is smaller than what that the filter says. Is this always like this or i have to find one with the rigth dimenssions?
Kory says
Hello Jay!
You will need to measure the length and width of the opening to the panel.
Jay says
I had a whole house filter installed on my furnace several years ago. Our house has always been dusty thus the whole house filter to try to filter out as much of the dust as possible. The old filter was tossed, but I still have the access panel. How do I measure for a new filter?
Naomi Mantonya says
I am looking for a fllter for a evaporator cooler. Model #12 300 HUMIDIFIER 2.20 A 120 VOLT 60HZ
Jade Brunet says
I am happy to have found this article about finding the air filter size you need in three steps. it is good to know that looking at the dimensions of the filter can be beneficial. It would be best to pay attention while removing the filter not to damage it. Something else to consider would be to seek professional help when choosing to ensure that the correct filter is purchased and that it is installed correctly.
Jorge McMillan says
I feel silly saying it, but I am one of those people who don’t know what size air filter I should get. With that being the case, I’m trying to learn all that I can about the process behind figuring out what kind of filter I’ll need. This article helped me a ton and I plan on starting with your first suggestion and figure out the dimensions I’ll need.