Find the right filter fit for your HVAC system
HVAC filter sizes vary based on your system, but the right fit is vital for its function and efficiency. If the specifications of the filter don’t match the HVAC system’s design, it won’t work properly (and could even sustain damage over time.) Luckily, determining the right HVAC filter size is a straightforward process, especially if you have the old filter handy. Here’s how to find the right size filter for your HVAC system and when to consult a local air conditioning repair service.
There is no standard size for HVAC filters, as they’re not standardized across types of air conditioners and HVAC systems. Filters are sized based on three measurements: Length, width, and thickness. While there are a few common sizes, the exact dimensions vary depending on the manufacturer, model, and type of HVAC system. For help determining the right size filter for your system, consult a local AC repair pro for recommendations.
Check out these common HVAC filter sizes:
| Width in Inches | Depth in Inches | Thickness in Inches |
|---|---|---|
| 6 | 25 | 1 |
| 20 | 25 | 1 |
| 20 | 20 | 1 |
| 14 | 20 | 1 |
| 16 | 20 | 1 |
| 20 | 25 | 4 |
| 16 | 25 | 4 |
| 20 | 25 | 5 |
To find the right size HVAC filter, look for the measurements printed on your current filter (if it fits properly). If your filter isn't labeled, grab a tape measure or ruler and measure each side of the filter—length, width, and thickness. Make sure to measure in inches for accuracy.
If your old air filter didn’t fit or if you don’t have it, you’ll need to measure the slot in your HVAC system. Turn off your system, open the compartment, and measure the slot's length, width, and depth. Remember, the filter's size should be smaller than the compartment's measurements.
A properly fitted air filter doesn’t have to seal tightly, but it should snugly fit in the filter compartment with a little space around the edges. It should also slide in easily without being forced. If you’re not sure what the correct size is, it’s a good idea to hire HVAC services to assist you in selecting the right size. While this task adds to your HVAC filter replacement cost due to potential trip fees and hourly rates, you can request an AC tune-up or other maintenance services during the visit.
Understanding nominal vs. actual HVAC filter sizes is a crucial part of finding the proper fit. The dimensions listed on the filter are the nominal size, which is an approximate measurement closer to the size of the filter compartment.
However, the actual size of your HVAC filter should always be slightly smaller than the filter slot— between ⅛ and ⅝ inches smaller. If your filter sits directly in a vent rather than a slot, your filter dimensions should only be about ⅛ inch shorter than the space.
HVAC systems can accommodate filters that are 1-inch thick, but if that’s your preference, a professional will need to install an external rack to hold it. Do not purchase a thicker filter without this accommodation. Thicker filters can handle more dirt, so you won’t have to change them as often. They also catch more particles. But be careful: too-thick filters can block airflow and cause HVAC problems.
While they don’t play into choosing the proper HVAC filter sizes, MERV ratings are still something you should consider, particularly if you have people in your household with allergies or other air sensitivities. So, what is a MERV rating on an air filter? Minimum Efficiency Reporting Value (MERV) assesses the capacity of an air filter to obstruct particles of specific sizes. For example, a MERV 1 filter can only stop particles larger than 10 microns, like big water droplets. But a MERV 20 filter can catch particles as small as 0.3 microns, even viruses and tiny dust.
While there are other rating systems like MPR and FPR, MERV is the best to reference because it’s most commonly used, making it easy to understand how well a filter works no matter what brand you’re buying.
Using the wrong HVAC filter size can lead to decreased efficiency, increased energy costs, and potential damage to the HVAC system. If you discover that you have the wrong size filter, it’s important to replace it promptly with the correct size. Unfortunately, trimming the filter down isn’t a viable solution, as it can create openings that permit dust, dander, pollen, and other indoor air contaminants. Contact a local HVAC technician to check up on your system and help you select the correct HVAC filter sizes.
