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When should I change the furnace filter?

Common Filters

Question. When should I change the Filter in my furnace or air handler?

This is a very common question. The answer depends upon several factors. The type of filter you are currently using and your enviroment.

There are many different types of air filters and each has it's own benefits and will capture airborne particles based upon the size of the particulate. The method to which a filters is rated is referred to it's MERV rating.

MERV Rating

Minimum Efficiency Reporting Value, commonly known as MERV Rating is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters.The scale is designed to represent the worst case performance of a furnace filter when dealing with particles in the range of 0.3 to 10 micrometres. The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range.

The common furnace filter

The common 1-inch thick, 99 cent fiberglass, filter that you can pick up at the department or dollar store captures very large particles in the air while allowing smaller particles such as dust and pollen to pass through. New installations usually come with this type of filter to prevent construction debris from getting into the blower. These filters have a MERV rating of less than 6, if at all.

HEPA filter

The opposite of these filters are the Box HEPA style filters and commonly referred to as media furnace filters. The letters in the word HEPA stand for High Efficiency Particulate Arrestance. The HEPA filter was developed during World War II by the Atomic Energy Commission and it was designed to remove and capture radioactive dust particles from the air which might escape and present a health hazard to the researchers. The HEPA filter was specifically designed to protect the Human Respiratory System.

For a filter to be labeled "True" HEPA, it must be certified 99.97% efficient in capturing 0.3 micron (not 0.1 or 0.01 etc..) respirable-size-particles (RSP) according to the U.S. Military Standard MIL-STD-282, commonly known as the DOP test. The reason 0.3 micron is used and no other is because 0.3 micron is the size at which all mechanical filters are LEAST efficient in capturing. Other methods of testing do not give a true picture of efficiencies relative to respirable-size-particle (RSP) capture.

These filters can be anywhere from 4" to 6" thick and may have a MERV rating greater than 10. These type of filters fit into a special box that is sold to consumers as an "add-on" or upgrade to their furnace or air handler. These filters are ideal for allergy sufferers as they remove very small particles such as pollen.

Pleated furnace filters

The middle range furnace filters are high efficiency pleated filters. These filters are made from non-woven fabrics designed to capture the mid-range particles while minimizing pressure drop, that is, the energy required to draw the air through the filter. Clogged filters produce increased stain on the blower motor which may result in costly pre-mature failure. This is one of the most important reason other than improving your indoor air quality to change your filters a regular basis.

Now that you have an understanding of the types of filters, how often should I change them? The least expensive filter needs to be changed at least monthly. The mid-range pleated filters usually lasts for about 3 months while the HEPA style filter will last for a year. The reason why the filters that capture the smallest particles lasts the longest is that type of filter has the most pleats which increases the surface area for the air to flow through.

While this timetable is the basic "rule of thumb", you will also need to consider the environment and other factors. If you live in a dusty climate, use your air conditioner more often or have pets you may need to change them more often. If you have a asthma or allergy sufferer in the house you may wish to upgrade to a higher MERV rating, upgrade your filtration system or change the filter more often.

How to change the furnace filter

change furnace filterChanging your furnace filter is a simple process. All you need to do is slide the old one out and slide the new one in. Be certain that the air flow arrow points toward the furnace or blower motor. Click here to learn how to change your furnace filter.

FiltersAmerica is a leading supplier of consumer air quality products including replacement HEPA filters, furnace filters, air cleaners, and home humidifier products. We search the market for the best value in replacement filters and humidifier pads and pass the value to our customers. FiltersAmerica stocks all HEPA filter, air cleaner filter, humidifier filters and ships directly from our own warehouse in Illinois. Did you know you could reduce your heating and air conditioning costs by up to 20% by changing your furnace filter?

Did you know - Have your heating & air conditioning cleaned and checked by a professional at least once a year to maximize running efficiency, comfort and safety.
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