Changing your indoor air filter regularly not only helps to protect your heating cooling systems from premature failure, but it reduces dust and harmful allergens that you and your family breathe. Each filter has a finite life depending on the type of filer and how much dust and other particles is in the air. Some filters are recommended to be changed no later than 30 days, some are rated for 90 days and, even as long as six months. It is important to know what works for your application
Most household and office indoor filters can be changed every 30 to 90 days depending on where they are being used, the number of hours the A/C actually runs, the amount of dust in your area (dust load), whether you have pets, or if there are smokers in the building among other considerations. Your maintenance technician can help with determining filter change frequency.
HVAC filters should be changed when they are dirty or on a frequency with which you feel comfortable that the filter should be changed. However, it is good practice not to exceed the manufacturer’s recommended duration. Some of our customers change MERV 8 filters every two weeks while others retain the filter for the recommended 90 days or more. How quickly filters become dirty depends on your environment. Proximity to busy highways, construction activities, pets and the number of occupants in your building will affect your indoor air quality and the frequency with which filters need to be replaced. A general rule-of-thumb in determining how often you should change your filter is to initially inspect your filter at least monthly and change them if necessary. This will help to determine if you should change your filters every 20, 30 60 or 90 days.
Check that your filter has the correct length, width and thickness as specified by the equipment manufacturer. It may also be useful to ask your HVAC technician to verify your filter size because duct work is frequently modified to fit the available building space and may be different from size specified in your equipment manual. Your filter should fit snugly into the filter grill slots, loose enough for easy installation and removal but tight enough to prevent vibration or air leaks around the filter.
Follow the direction of the arrow printed on the side of the filter if there is one. The arrow should be pointed in or up depending on the location of your air handler filter grill. If your filter has no directional arrow, or has only one face reinforced with a metal mesh or cardboard grid, turn the reinforced face towards the air handler. The reinforced face ensures that the filter medium is not drawn into the blower during operation.
HVAC filters are normally installed in a grille which houses the filter. The HVAC industry sometimes specify the filter by the standard industry filter grille size commonly referred to as the nominal size. However, the actual filter must be somewhat smaller than the grille to fit into the unit, therefore filter manufacturers will size the actual filter to fit the grille size specified. For example, your A/C unit may call for a 20” X 20” X 1” filter (grille or nominal). The manufacture may make a filter 19 ½” X 19 ½” x ¾” (actual size) which is an undercut from the nominal size.
There is a list of industry sized filters that are generally considered to refer to the size of the filter grille installed by the manufacturer of your HVAC unit, these are the nominal sizes. Unless otherwise stated by the customer when ordering, filter manufacture will consider these sizes grille or nominal and will make a filter with dimensions ¼ to ½ inch less than the stated/nominal size.
Minimum Efficiency Reporting Value (MERV) is the industry standard mostly used in the USA to measure the efficiency of A/C filters. MERV rates the overall effectiveness of air filters and therefore higher MERV ratings results in finer filtration which allows fewer dust particles and other airborne contaminants to pass through the filter.
The best filter for your air handler depends on your individual preferences, costs and system design. A typical MERV 4 to Merv 8 filter is usually sufficient for most applications. If someone in your household has upper respiratory problems, if you have pets or your dust load is high, you should consider filters with a higher MERV rating than the typical MERV 7 or 8 filter. If you have an odor problem a carbon filter may help. Some air handlers perform more efficiently using filters with lower MERV rating, because lower MERV rating filters typically result in a lower pressure drop across the filter.
Carbon or charcoal impregnated filters help with odor management. They can be made in the pleated or non-pleated form.
Indoor air quality (IAQ) is a measure of the aerosols, gas content, dust load, temperature, and humidity of the air inside a building. The desired indoor air quality is determined by the need to maintain the health and well-being of the people occupying the structure, and the type of the products being handled within the structure. For example, some manufacturing processes such as sensitive electronic products require high IAQ.