Air Filter

Finding Balance – MERV Ratings and Air Flow

When folks in the industry talk about filter efficiency, our concern is with how good of a job each filter does with removing contaminants and particulates from the air. We’ve talked a lot before about the different MERV ratings and what kind of contaminants are removed, and finding the right MERV rating for you. But one thing we don’t always consider is energy efficiency – do different MERV ratings have an effect on how hard your furnace, air conditioner, or HVAC unit has to work to push air through the house? The answer is, “Yes, they do.”

MERV Ratings

The MERV scale is pretty simple – the higher the number, the more “stuff” it will remove from the air. A filter with a MERV 8 rating, for instance, is a good everyday filter, and will remove large particulates from the air and protect your HVAC unit from the damage that unfiltered air can cause. A MERV 11 filter is appropriate for homes with pets or people with allergies, because it picks up most allergens, including pet dander. A filter rated MERV 13 or higher is appropriate for people with asthma, and will remove the most contaminants from the air.Air Flow

The Trade Off

It’s important, however, to balance the effectiveness of these filters with the corresponding energy costs. A higher MERV rating means the filter is more restrictive. It removes more contaminants from the air, but it means that your furnace or air conditioner has to work harder to push the air through your home. Using a filter with a higher MERV rating could mean that your HVAC system runs longer than it would with a filter with a lower MERV rating.

Which Filter is the Right Filter?

If you or someone in your home suffers from asthma, choosing a higher MERV rating is probably the most appropriate way to go. But if not, it’s probably not necessary to use such a restrictive filter. If you don’t have any pets, or only suffer from seasonal allergies, you might choose to only use a more restrictive filter during allergy season, when allergens are more present in the air, rather than all year long. Choosing the right filter is a balance between how much you need to remove from the air and how much energy your furnace or air conditioner uses to push the air through your home. At, we carry filters from a number of manufacturers in a variety of MERV ratings, so we always have the right filter for you.

2 thoughts on “Finding Balance – MERV Ratings and Air Flow”

  1. Who rates filters? What does hvac stand for? Do you sell a vacumn meter or some other device to help determine when it is time to change filters. If you can still see light when you hold a dirty filter up to a light, is it to soon to replace? Does a filter develope a higher merv. rating as it becomes dirty? What merv rating do I need to keep colling coil on my groundwater heat/coiling copump from getting dirty? It develope condensate in the cooling cycle. Please send your coments to my E-mail, thanks . Ken

    • Hi Ken,

      I’ll answer your questions in order:

      1. Filters are rated on the MERV scale, which is an industry standard measure developed by ASHRAE. You can read more about MERV ratings here.
      2. HVAC stands for Heating, Ventilation, and Cooling.
      3. There are a couple of different tools to tell when it’s time to change your filter: a simple timer, a filter gauge by GeneralAire, and a filter monitor/clog detector by FILTERSCAN.
      4. By and large, a dirty filter will be coated with a layer of visible dirt and dust that will prevent light from getting through, but you should refer to your owner’s manual for your HVAC system to determine how often the filter should be changed.
      5. As a filter collects dirt, dust, and other contaminates, it will develop a higher MERV rating. Keep in mind that a higher MERV rating means decreased air flow, which keeps contaminates out of your air, but also means that your HVAC system has to work harder to control the temperature in your home, which can result in higher energy costs and more wear and tear on your system.
      6. Originally, filters were developed for HVAC systems to keep dirt and dust from getting into the system. Any filter will keep the large particles from getting through – even the cheap, unpleated fiberglass filters. Higher MERV ratings are designed to improve your indoor air quality by capturing allergens like pet dander and pollen, bacteria, and mold. You can find out more about which MERV rating is appropriate for you here, and you can read about the effect an air filter has on your coils here. Also, you should check your owner’s manual to see what sort of filter the manufacturer recommends.

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