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How to Choose a Good Quality Filter for your Furnace

Tips For Selecting a Portable Air Cleaner, Furnace Filter, or HVAC Filter When selecting a portable air cleaner, furnace filter, or HVAC filter, keep in mind: No air cleaner or filter will eliminate all of the air pollutants in your home. Note that most filters are designed to filter either particles or gases. So in order to filter both particles and gases, many air cleaners contain two filters, one for particles and another for gases (in some cases including gases that have odors). Other air cleaners only have one filter, usually for particles. In addition, some air cleaners or filters are targeted to specific types of gases or VOCs. Consult the specific product packaging or labeling for more information. All filters need regular replacement. If a filter is dirty and overloaded, it won’t work well. PORTABLE AIR CLEANERS To filter particles, choose a portable air cleaner that has a clean air delivery rate (CADR) that is large enough for the size of the room or area in which you will use it. The higher the CADR, the more particles the air cleaner can filter and the larger the area it can serve. Most air cleaner packaging will tell you the largest size area or room it should be used in. Portable air cleaners often achieve a high CADR by using a high-efficiency particulate air (HEPA) filter. To filter gases, choose a portable air cleaner with an activated carbon filter or other filter designed to remove gases. Note that there are no widely used performance rating systems for portable air cleaners or filters designed to remove gases. The CADR rating system is for particles only. Activated carbon filters can be effective, provided that there is a large amount of material used in the filter. A portable air cleaner with a high CADR and an activated carbon filter can filter both particles and gases. Generally speaking, higher fan speeds and longer run times will increase the amount of air filtered. An air cleaner will filter less air if it is set at a lower speed. More air will pass through the filter at higher fan speeds, so typically filtration will be greater at higher fan speeds. Increasing the amount of time an air cleaner runs will also increase air filtration.


FURNACE AND HVAC SYSTEM FILTERS Furnace and HVAC filters work to filter the air only when the system is operating. In most cases, HVAC systems run only when heating or cooling is needed (usually less than 25% of the time during heating and cooling seasons). In order to get more filtration, the system would have to run for longer periods. This may not be desirable or practical in many cases since longer run times increase electricity costs and may also result in less reliable humidity control during the cooling season. Q&A: Air Cleaning and Filtration Furnace and HVAC filters for homes are usually designed to filter particles. If you decide to upgrade or use a higher efficiency filter, choose a filter with at least a Minimum Efficiency Reporting Value (MERV) 13 rating, or as high a rating as your system fan and filter slot can accommodate. You may need to consult a professional HVAC technician to determine the highest efficiency filter that will work best for your system. Other devices that do not have filters may also remove particles and gases. They usually fit inside the HVAC ductwork and are more common in large and commercial buildings. See the EPA technical document, Residential Air Cleaners, 3rd edition, for more information: www.epa.gov/indoor-air-quality-iaq/ residential-air-cleaners-second-edition-summary- available-information. EPA does not certify or recommend specific brands or models of air filters or portable air cleaners. Do portable air cleaners and furnace/HVAC filters used in homes have the potential to improve my indoor air quality? Yes. Most portable air cleaners and furnace/HVAC filters can filter particles from the air. Some can filter the small particles of greatest health concern (PM2.5). There are also air cleaners and filters that can filter both particles and gases. The longer the air cleaner runs, the more air it filters. Note that it is always important to reduce or remove the sources of indoor air pollutants and to ventilate with clean outdoor air. Filtration does not replace the need to control pollutants and ventilate. Can portable air cleaners and furnace/HVAC filters potentially have a positive impact on health? Possibly. Several studies using portable HEPA air cleaners have demonstrated small improvements in cardiovascular and respiratory health. The improvements are typically small and not always noticeable to the individual, although they may be measureable by health professionals. For more information on particles and health, see:

  • EPA Indoor Particulate Matter: www.epa.gov/indoor-air-quality-iaq/indoor-particulate-matter

  • EPA Particle Pollution and Your Health: www3.epa.gov/airnow/particle/pm-color.pdf

Can portable air cleaners and furnace/HVAC filters reduce allergy or asthma symptoms? Possibly. Multiple studies with portable HEPA air cleaners have found improvements in one or more allergy and/or asthma symptom(s). The studies do not always show major improvements, and they do not show improvements in all symptoms. Can portable air cleaners and furnace/HVAC filters solve mold problems? No. Portable air cleaners and furnace/HVAC filters do not address the cause of mold and musty odors. Mold is caused by a water or moisture problem in the building that allows the mold to grow. To solve a mold problem, get rid of the source of the moisture and clean up the mold. Portable air cleaners and furnace/HVAC filters may remove some of the particles generated by mold. In some cases, they may also help reduce odors, but they will not resolve a mold and moisture problem. Note: Avoid portable air cleaners and furnace/HVAC filters that intentionally produce ozone. Ozone is a lung irritant. Note that in some cases, air cleaners that contain electrostatic precipitators, ionizers, UV lights without adequate lamp coatings, and plasma air cleaners may have the potential to emit ozone. Both the California Air Resources Board and the Association of Home Appliance Manufacturers maintain lists of air cleaners that have been tested and shown to emit little or no ozone. Q&A: Heating, Ventilation, and Air-Conditioning (HVAC) System Filters and Furnace Filters How are HVAC/furnace filters rated? There are several commonly used filter rating methods. These include the Minimum Efficiency Reporting Value (MERV), Filter Performance Rating (FPR), Microparticle Performance Rating (MPR), and others. MERV is based on a national consensus standard. The FPR and MPR rating methods are proprietary. For all rating methods, the higher the filter rating, the higher the removal efficiency for most particle sizes. How do I choose an HVAC/furnace filter that will be most effective at removing small particles of greatest health concern (PM2.5)? Use the highest-rated filter that your system fan and filter slot can accommodate. Filters with a MERV of 13 and above are required to demonstrate at least 50% removal efficiency for the smallest particles tested. This is an example of a label from a portable air cleaner. Used with How do I know if my system can accommodate a MERV 13 filter or higher? Most furnaces and HVAC systems can accommodate a MERV 13 filter without creating equipment problems, provided that the filter is replaced frequently. Sometimes it can be difficult to tell whether a system can use a higher efficiency filter since HVAC systems are not commonly labeled with any filter recommendations. To be certain a filter will work with your system, consult a professional HVAC technician. The technician can determine the most efficient filter that your system can use. An HVAC technician can also modify the system to use a higher efficiency filter. How can I tell if the filter is the right size for my furnace/HVAC system? Filters commonly come in thicknesses of 1 to 5 inches, with a variety of lengths and widths to match common sizes of filter frames in furnaces and HVAC systems. Make sure the filter fits snugly so air does not leak around the filter and you do not have to bend or crush the filter to make it fit. How often do I need to change my filter? Replace filters according to manufacturer’s recommendations. Many factors can affect how quickly filters get dirty. Manufacturers typically recommend replacement every 60 to 90 days. If you notice that filters appear heavily soiled when you replace them, you should consider changing them more frequently. What if I have a window air conditioner or a wall-mounted “ductless” air conditioner? Most window air conditioners and wall-mounted units are intended for temperature control rather than air filtration. These units typically have limited filtration intended to keep the inside of the air conditioner clean rather than remove fine particles from the indoor air.

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