MERV shows difference in filters

Belleville News-DemocratJanuary 15, 2014 

Q. Furnace filters used to cost 50 cents each. I saw an advertisement this morning showing two for $19. The ad claimed they were they better at catching dust, pollen, etc. I have used the more expensive filters, and the house seems just as dusty. What gives -- and please consult an unbiased party for the answer.

-- T.N., of Fairview Heights

A. I'm not sure who you would consider "unbiased," but maybe a few facts from the American Lung Association coupled with technical information from the Environmental Protection Agency will help everyone breathe easier.

Both stress that filters clearly are not created equal when it comes to keeping your home's air clean. And while not perfect by any means, filters that promise to trap more dust and dirt generally can prove their boast scientifically. Here's why:

The small gunk flying around your house comes in all shapes and sizes, from the larger dust mites and pollen to smoke particles, viruses and bacteria. Their size is measured in microns, a tiny, tiny unit of length.

To give you an idea of how tiny, a human hair is about 70 microns wide yet our body has defense mechanisms that can keep things as small as 3 to 5 microns wide out of our lungs. Still, the lung group says, the tiniest particles make up 99 percent of the debris in the air and many of these can get through the nose, sinuses and windpipe and into the lung. So you obviously want to keep as many of these out of your home's environment as possible.

That's why you put filters in your furnace -- and which filter you use can make a difference. For example, the cheap, flat, inch-thick, fiberglass panel filters are generally worthless, the lung group contends.

"The primary function of these filters is to protect the fan and minimize the amount of dust on the heating and cooling coil," it says. "These filters do little to remove contaminants from the air."

Instead, it recommends looking for pleated filters, because they have more surface area to trap contaminants. Better yet, look for high-efficiency pleated filters. That's why when you walk into large hardware stores today, you're confronted with such an amazing array of filters.

So how do you choose? Here's one key way: In 1987, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) designed a new scale to rate the effectiveness of air filters. It's called MERV, the Minimum Efficiency Reporting Value. Now, filter packages usually show a MERV number from 1 to 20, the higher the better.

For example, a window air conditioner may contain a filter with a MERV rating of 1-4, which generally can't block much of anything smaller than 10 microns. Once you get up to MERV 8, you're stopping mold spores and pet dander, but it's still letting through more than 30 percent of everything down to 3 microns -- and anything smaller. That's why if you're fussy about your air, you'll want to pay extra for double-digit MERVs that can stop particles down to 1 micron and beyond.

"When buying filters, look for the highest efficiency filter that works with your furnace," the lung group says. "Health House (an association resource for healthier homes) guidelines require a MERV rating of 10 or higher."

And, like those smoke alarm batteries you're always reminded about, don't forget to check your filters regularly.

"Efficiency will change over time," the lung association says. "As filters become loaded with particles, the available openings for air to flow through become smaller. The result is better filtration but less air movement, causing your furnace to work harder. Disposable filters need to be replaced on a regular basis."

HEPA (High Efficiency Particulate Air) filters generally can't be used on your average furnace because they impede air flow too severely, so the severely allergic may want to invest in electronic air cleaners, UV cleaners and other devices. But before you criticize the efficiency of the more expensive filters, remember that a good deal of the stuff floating in your house comes from other sources. Since your furnace isn't designed to be a whole-house air cleaner, these particles settle quickly, ready to fly up again when disturbed.

For an even more comprehensive look at filters and air cleaners, try

Today's trivia

What must-have household necessity resembling a bayonet and sickle did Ezra Warner patent in 1858?

Answer to Wednesday's trivia: By 1873, German immigrant brothers Frederick and Louis Rueckheim had become a popular fixture selling popcorn on the streets of Chicago. Then, in 1896, they found a way to keep kernels of molasses-covered popcorn from sticking together. One of the first people to sample it reportedly exclaimed, "That's a crackerjack (slang for excellent)!" -- and a new snack sensation was born. In 1918, Cracker Jack added Sailor Jack and his dog, Bingo, as mascots, with Jack modeled after the Rueckheims' young nephew Robert. But Robert never enjoyed his celebrity; shortly after the image debuted, he died of pneumonia at age 8.

Send your questions to Roger Schlueter, Belleville News-Democrat, 120 S. Illinois St., P.O. Box 427, Belleville, IL 62222-0427 or or call 618-239-2465.

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