Do Pleated Air Filters Restrict Airflow? What the Research Shows
Yes, a little. A pleated filter catches more dust than a flat fiberglass one, and that means more resistance to the air your blower pushes through it. In field studies the airflow drop was usually single digits to about 11 percent. The EPA still says most home systems can run a MERV 13 filter without problems, as long as you change it often.
What the EPA says
The EPA’s Guide to Air Cleaners in the Home recommends a furnace or HVAC filter rated at least MERV 13, or as high as your system fan and filter slot can take. Its answer to whether a system can handle that is direct: most furnaces and HVAC systems can, “provided that the filter is replaced frequently.”
The EPA adds two cautions. HVAC systems are rarely labeled with filter recommendations, so if you want to be certain, ask an HVAC technician. And running the fan longer to filter more air raises electricity costs and can make humidity control worse in the cooling season.
What field studies measured
The best-known numbers come from California research for the state Energy Commission, summarized by John Proctor in the ASHRAE Journal in October 2012 and explained in plain terms by Energy Vanguard:
- HVAC design assumes a filter pressure drop of about 0.10 inches of water column. In two test systems, a low-MERV filter (under MERV 4) was right at that, a MERV 8 filter was about 0.19 and a MERV 11 filter about 0.32.
- Airflow with the MERV 11 filters was 7% and 11% lower than with the low-MERV filters in the two systems. With the MERV 8 filters it was 3% and 8% lower.
- Across 34 California homes, the average pressure drop across the installed filter was 0.28, close to three times the design assumption.
A 2009 Home Energy article by David Springer of the Davis Energy Group found that resistance doesn’t climb evenly with MERV rating. The big jump comes when you move from a basic 1-inch fiberglass filter to the first pleated grade. It also found a trend toward lower airflow with higher-MERV filters in systems with standard (PSC) blower motors.
Why a pleated filter can still be the right choice
- A dirty filter restricts airflow more than a clean pleated one. The EPA’s condition is frequent replacement. A pleated filter left in for months is the real problem. See how often to change a furnace filter.
- Thicker filters have less resistance. The same air spread over more filter area moves through more slowly. If your system has a 4 or 5 inch filter cabinet, a deep filter at the same MERV rating is easier on airflow than a 1-inch one.
- The right size matters. A filter that leaves gaps lets air bypass it, and one that is forced in can bow. Check the nominal and actual size on the air filter size chart.
- Direction matters. Install it with the arrow pointing toward the furnace. See which way a furnace filter goes.
When to step down or call a technician
If you switched from fiberglass to pleated and the system now seems to struggle, the EPA’s advice applies: an HVAC technician can tell you what your system can handle. Until then, a MERV 8 pleated filter, changed on schedule, is a middle step between fiberglass and MERV 11 or 13.
Need a replacement while you’re there? Read the size printed on the old filter’s frame first (our air filter size chart explains nominal vs actual size). For the four most common sizes:
16x25x1 · 14x20x1 at Air Filters Delivered · 20x25x1 · 16x20x1 at Factory Direct Filters. Other sizes: use the HVAC filter finder. (Affiliate links: we may earn a commission at no cost to you.)
Frequently Asked Questions
Will a MERV 13 filter damage my furnace?
For most home systems, no. The EPA says most furnaces and HVAC systems can take a MERV 13 filter without equipment problems if the filter is replaced frequently. If your system is older or has a small return, ask a technician first.
Is a fiberglass filter better for airflow?
It has the least resistance, but it also catches the least. In the California studies, moving from fiberglass to the first pleated grade caused the biggest step up in resistance. Higher grades added less on top of that.
Do I need a thicker filter to use a higher MERV rating?
Not always, but it helps. A deeper filter at the same rating spreads the air over more media, so it resists airflow less than a 1-inch filter. You can only use one if your filter slot or cabinet is built for that depth.
Sources: EPA, Guide to Air Cleaners in the Home; Energy Vanguard summary of Proctor (ASHRAE Journal, 2012) and Springer (Home Energy, 2009).