Air Filters

During the Manhattan Project, when we started figuring out how to use nuclear power, we discovered we had to clean radioactive gas out of the air. To do this, researchers developed a HEPA media filter.  Fast forward a few years into the future, and you can find HEPA filters in everything from vacuums, to cars, to your home’s heating and cooling system. While great for filtering the air, most of our home systems can’t pull air through a HEPA media filter.

For a long time, there was no standard for particulate removal. Finally, some HVAC manufacturers got together and developed a standard to test filters. They called it MERV. The higher the MERV, the more and smaller particles it could capture. We now have some systems that use MERV 16 media. In some cases, this loads up too quickly to be practical. (Higher MERV numbers usually means higher cost per filter as well.) Most systems work well with a MERV rating between 8-13. If a customer chooses a MERV 13 media that is only 1” deep this can sometimes lead to over taxing the equipment.

I have been installing Aprilaire filters for my customers for years. About 8 years ago, they completely redesigned their filter to make it more acceptable to the mass market. I can’t say this improved the performance of the product, but it made it a lot easier to replace and install. The new design is sufficiently good to endorse. The only down side is you have to buy replacement media from a contractor or the web, whereas Honeywell box filters can be purchased at Home Depot and Lowe’s. What I love about Aprilaire is it is designed to be replaced once a year. Also, Aprilaire guarantees their filter will keep the system clean. I have been using these in my own home and am extremely happy with them. I have installed probably several hundred and they always perform better than others.

What about electronic air cleaners? Well, they were a real innovation when they were introduced. They charged a particle and captured it on a grounded plate. They work really well on most particles, but they don’t work at all on others. Also, they prefer the particle to be gently wafted past them. Modern furnaces work hard to deliver air and the velocity of the particles makes them zip past the grounded plates and the charging wires. Also, electronic air cleaners work best when they are new and clean – which means they need to be regularly washed. The dirtiest systems I have seen in the field have had undermaintained electronic air cleaners.

A passive media filter just gets dirtier and dirtier, but most eventually get clogged. The Aprilaire media can be clogged too, but is much less likely to do so. A homeowner will usually discover they need to change it, before the filter stops working.