When it comes to furnaces, the air filter you use can make a big difference. High-efficiency MERV filters in the range of 8 to 13 can eliminate 90 percent or more of dust particles and allergens. Pleated filters, which are made of paper and polyester, are the most common type and can filter out most household particles and allergens well. Permanent reusable filters, also known as washable filters, are made with a solid aluminum or plastic frame and are more efficient than disposable filters.
Fiberglass filters, however, are not as effective and need to be checked and replaced more frequently. It's important to know what type of air filter to buy, but it's also important to know where your air filter goes in the first place. If your HVAC unit is installed in the attic, for example, the filter may be installed in a ventilation grille rather than in a return duct. A traditional forced-air oven draws air through the return ducts, heats it over a heat exchanger and then pushes the hot air through a series of ducts that branch out into rooms throughout the house. When choosing an air filter, you should also consider the MERV rating.
MERV stands for Minimum Efficiency Reporting Value and is the technical language of how good an air filter is at trapping dust particles and preventing them from recirculating in your home. A MERV 16 air filter is great for trapping dust particles and allergens, but it's important to make sure your HVAC system has a fan powerful enough to work with it. To find out what size air filter you need, take a look at your current filter and you'll see an arrow located somewhere along the edge of the filter. You'll end up with three numbers (in inches), which is the size of the air filter you need (usually indicated as something like 16x25x1 on the side of the filter).
This website provides a basic conversion from MPR to MERV, which should help you if you change the brand of air filters that use different classification systems.