Do Air Filters Reduce Airflow? An Expert's Perspective

If you have a dirty air filter, it can cause low airflow. Not only does it restrict airflow, but it makes the entire HVAC system work harder, not as efficiently as possible.


, pleated air filters restrict airflow to your HVAC system. However, you should keep in mind that all air filters will restrict airflow to a certain extent, it's a fact. What you want to worry about is finding the right filter for your unit and your overall system to ensure you reduce the amount of contaminants in the air as much as possible.

Studies have shown that high MERV filters can reduce airflow by up to 11% compared to low MERV filters. Similarly, medium MERV filters also showed a decrease in airflow relative to the low MERV filters, this time 3% and 8% lower in both systems. As filtration efficiency increases, so does the system airflow restriction caused by the filter. Therefore, HEPA filtration is not suitable for all residential systems. An HVAC contractor can measure airflow and tell you if your system can support HEPA filtration in the duct.

Alternatively, residential HEPA filtration options include whole-house air filters that connect to the duct network via a bypass circuit. These units draw air from the duct, transport it through the HEPA filter assembly, and then loop it back into the duct without restricting airflow. Why don't we like them? Because they restrict airflow to your HVAC system. High MERV pleated filters definitely capture a lot of contaminants, but they also restrict air movement to the blower or oven. As a result, the fan has to work harder to heat and cool your home, reducing efficiency.

These filters can also cause liquid to return to the compressor, which will cause premature equipment failure. So what can you do to be able to use a high MERV* filter and not suffer a high pressure drop across the filter and consequent loss of air flow (PSC blower) or increased energy use (ECM blower)? In fact, it's quite simple. In my opinion, the air cleaners should be in the return air grilles, not in the equipment. Through this site and the trails it led me along, I have learned that two MERV 11 filters can have the same filtering capacity, but one could allow more air to be transferred. Another way of looking at it is that a system that lasts 96 months with a fiberglass filter would last about 93 months with a pleated filter, a difference that is practically negligible, and again, it doesn't take into account other factors that contribute to wear and tear. Standard panel filters have MERV ratings of 1 to 4 and generally remove air particles no smaller than 3 to 10 microns.

These cover all the basics of air filtration (dust and pollen removal, for example) without restricting air flow. So what should you do if you have a return grid filter system or if your ductwork can only accommodate 1 filter in the chamber? We recommend avoiding high MERV 1 filters (above MERV 8 is quite restrictive). However, this is the case with any oven filter that removes contaminants and dust from the atmosphere within its property, as it will continuously filter the air. Because HEPA filters contain incredibly dense filter media, they usually require an additional fan to push air through the filter. You don't want to spend time and money choosing an air filter only to find out that you've bought one that isn't going to do the job you ideally want your filter to achieve.

Another reason is that HVAC problems caused by a clogged air filter are incorrectly attributed to the filter, not to a lack of change. A media filter lives between the return chamber and the furnace, so the system may require some reconditioning if it is not already configured for one. When you are considering what type of air filter to install in your home, make sure you research and know what you are really looking for, otherwise you could end up buying one that will cause more problems in the future.

Kristy Letman
Kristy Letman

Typical music practitioner. Professional beer enthusiast. Hipster-friendly pop culture buff. Proud travel geek. Proud social media fan.

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