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What is a MERV Rating? Understanding the Effectiveness of Air Filters

MERVRatingAirFilterWe talk about air filters often in this blog, and that’s because it really is one of the easiest and most important things to take care of to maintain your home’s HVAC system, and essentially, your home’s comfort. Picking a good filter for your home and understanding the efficiency of it has gotten easier with a ranking system – called a MERV rating – that grades filters on their effectiveness.  Here’s how understanding the MERV rating will help when you’re in the hardware aisle, picking out your next filter. 

Understanding MERV

MERV stands for “Minimum Efficiency Reporting Value.” It’s how the HVAC industry ranks air filters’ effectiveness and allows pros and homeowners alike to compare air filters. The easy way of thinking about it is that filters with higher ratings provide better filtration and are usually more expensive because they are more efficient. Lower rated filters are less expensive, but don’t collect as much debris from your air. 

However, it’s not as simple as picking out a higher rated filter to just get better efficiency. Picking a filter is also about providing proper airflow for you home, something that your HVAC system may not be equipped for if you pick a filter with a higher MERV rating.

Keith Hill, technical support manager for Minnesota Air, reminds homeowners that higher MERV filters require more horsepower to push or pull air through them. 

“If your system does not have enough oomph, you may have trouble with your heating and cooling equipment, possibly even do damage,” he says. “Your system needs a minimum amount of air to reject the heat or your furnace will overheat, and the same for cooling, or your A-coil (part of the AC that helps cool the air) will get too cold and freeze.”

Keith also says that it’s important to note that not all dirt and allergen particles are created equally. 

“MERV as an indicator of efficiency roughly means the amount of dirt and particles that the filter removes from the air stream, but there are big particles, little particles, and microscopic particles,” he says.

So what does that mean to you when picking a filter? Keith explains that a filter with a MERV rating of 6 is only 85 to 90 percent effective at removing particles the size of cement or sheet rock dust but is 99.9 percent effective at removing textile fibers, dust mites, pet dander, and larger pollen spores. 

“If you are not concerned about these smaller particles, why spend the extra money on a more expensive filter that you will have to change more often,” says Keith. “Higher efficiency filters plug up sooner.”

What Does MERV Mean For My House?

The bottom line is: you don’t want to spend money on a better filter just because the MERV rating is higher. Keith breaks it down like this:

For residential use, a filter with a MERV of 6 or 8 is more than enough for most people. 

For those with allergies to dust and smaller pollen particles, choose a MERV of 8 or 10. 

Nevertheless, if your system is already working to capacity regarding airflow, adding a more restrictive filter can create trouble, Keith says. That’s where choosing a thicker filter can help. If you read our Filters 101 Guide, you’ll see that a thicker filter allows for better airflow and efficiency, but may require some duct modifications to use it. In some cases with undersized ducts, even a MERV 6 can be problematic, so when in doubt, ask a pro before installing a high-efficiency filter.

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