Which Air Filter Should I Use?
March 7, 2010 Indoor Air Quality
With so many options, choosing a filter can be confusing and frustrating. You walk through the store and there are just too many options; 30-day filters, 90-day filters, washable filters, electronic filters, and on the list could go. So, what is the best filter?
Understanding MERV Ratings
Some people would tell you that the most important thing to consider when purchasing a filter is the MERV rating. MERV stands for Minimum Efficiency Reporting Value. This relates to the number of particles that are removed by the filter as air passes through it. Basically, the way a MERV test works, is they take a filter and set it up to have air pass through it that is filled with particles. As the air passes through, a measurement is taken before the air passes through the filter of how many particles are contained in it. Once it passes through the filter, another measurement is taken, to determine how many particles were removed by the filter. From there, a MERV rating is assigned to it based on how small the particles were that it caught, and what percentage of those particles were removed. The higher the MERV rating the better it was at catching the small stuff (MERV ranges from 1-16)
So, if a filter is 99% efficient, that’s the one to buy! Right? Wrong! One thing that people often miss is at what size the filter is efficient. Let me illustrate it this way: if I take a basketball and throw it at a chain link fence, what are the chances that it’s going to make it through? Slim to none. So, I could honestly say that my chain link fence is at least 99% effective at stopping particles from passing through it. At least, particles the size of a basketball (ah, the good ol’ fine print). Take the same fence and throw a cup of peas at it, now all of sudden the efficiency drops drastically. The same is true with filters. A filter may be 99% effective but at 10 microns, it’s really not catching a lot. We could get into a whole discussion about microns, and what we can and can’t see, etc. but that’s a wh
ole different article. So here it is: Unless the filter is effective at sub-micron levels, it is not doing too much good. It is stopping the basketballs, but things that are smaller, are making there way through the filter. So when you read the label, read the fine print!
The Importance of Air Flow
Another aspect that many people fail to consider when selecting an air filter for their system is air flow. Remember, it is an air conditioner, so it needs air to condition! Some, very efficient filters, are highly restrictive on air flow. Back to our illustration about the fence, basketballs, and peas. If I took a piece of plywood and threw a basketball at it, it would stop it. If I threw a cup of peas at it, it would stop them. I could throw just about anything at it and it would stop it! So should you just by a piece of plywood and nail it over your air return? Not quite. Because, while it may be 100% effective at stopping particles, it’s also 100% effective at stopping air flow. So, no good. Some filters, while very effective at removing particles from the air, also restrict air flow greatly. Some of the heavily pleated filters and others, can starve your system of air it needs.
So, Is there a Good Solution or Not?
Yes there is. A great solution is using an electronic air filter in your system. Electronic filters work by having a board that sends voltage through the media placed on top of it. With the media electronically charged, it attracts particles to the filter, catching them before they recirculate throughout your house. This is great for a couple reasons. First, many filters are 95-99% at sub-micron levels, meaning that everything down to cigarette smoke can be caught in the filter (pretty awesome huh?). Second, they are excellent on air flow, because they are not relying on sheer thickness to stop stuff from getting through. Many of them, you can see right through! The downside? They can be a bit pricey. You should expect to pay anywhere from $500-$1,000 for one, not including replacement media each year. That’s an important factor too. Some units can cost up to $200 for replacement media each time (You’ll be changing this 3-4 times a year). So, do your homework, and get a good value out of it.
Should you need any recommendations, feel free to call me and I will be happy to talk to you more about the subject. Take care, and good luck filter shopping!
