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It may surprise you to learn that indoor air pollution is among the top five environmental health risks. That's why we've been devoting a series of posts on air filtration. If you've been watching and listening to our posts, you've heard us talk about the MERV ratings of air filters, and how to select the best air filter for your needs. As a general rule, prices are higher for filters with higher MERV ratings. But here is one instance when the buying the best, most expensive filters those with MERV ratings greater than 16 may do more harm than good.
Among the most expensive filters are HEPA filters. Higher efficiency filters with a MERV rating of 14 to 16, are sometimes misidentified as HEPA filters. But true HEPA filters have MERV values of 17 to 20. HEPA which stands for High-Efficiency Particulate Arrestance - is a special type of filter that, according to DOE standards, filters out 99.97% of particles down to 0.3 microns in sizeâ€¦ that's 10 times smaller than a MERV 16 filter! HEPA filters are typically used in biomedical applications to filter out bacteria and viruses.
More Harm Than Good
True HEPA filters those with MERV ratings 17 and above - are normally not installed in residential HVAC systems. A typical residential air handling unit and associated ductwork cannot accommodate HEPA filters. They do not have enough fan or motor capacity to accommodate the large pressure drop across the dense HEPA filter material. If you install a HEPA filter in an HVAC system not specifically designed for it, it will make your motor work harder because it is getting too much resistance, and this will hamper your airflow, increase fan noise, and cause your system to fail earlier. Check with your HVAC manufacturer prior to upgrading filters to determine whether it is feasible to use more efficient filters.
Let's Get Real
According to the EPA, using medium-efficiency filters, such as those with a MERV rating of 12-13, are almost as effective as true HEPA filters at removing allergens, with much lower associated system and operating costs, and quieter fan operation. Furthermore, many air particles never go through your HVAC filter system because they are deposited in your living space on your sheets, furniture, and carpet, for example. So, you still need to change your sheets, vacuum, and do all those house-cleaning chores regularly to maintain your indoor air quality.
Things You Can Do
Here are some other simple things you can do to improve your indoor air quality:
Prevent mold by controlling moisture throughout your home. That means turning on exhaust fans in bathrooms while showering, and making sure your basement and crawlspaces are dry.
Fix any leaks in your ductwork, in the roof, around windows and doors, and around plumbing fixtures.
Keep your home smoke-free. Do not smoke indoors, don't burn candles and incense, and use exhaust fans while cooking.