Forced Air heating & cooling systems have filters to protect the equipment. The standard filter has a loose mesh of fibers design to keep the fan and coils from clogging with dirt. The mesh maybe washable such as foam or aluminum which requires frequent cleaning. These have a typical MERV rating of 1 or 2 and catches the chunky stuff. It meet the minimum requirements for the equipment manufactures. Very common to find these ship with equipment and commercial service contracts. These need to be changed often and can fall apart easily. They do little to protect the equipment and nothing for the occupants. Have you ever seen, white ceiling diffusers covered in dust & dirt? This happens with low end filters and poor maintenance.
For our clients, we use a pleated style filters which have a larger surface area for air to pass through and a finer fabric material. These filters cost 4- 6 times more than a MERV2 filter but can be changed less often. Most of our commercial accounts only need to be service twice a year instead of the standard 4 times per year. This reduces operating cost for our clients because technician times cost a whole lot more then the filters.
These filters have a typical rating of MERV 7 or 8 and offers good protection for the equipment. It will catch most particles in the 5-10 micron range. It improves the air quality by reducing dust and reduces cleaning cost for the occupants. The white ceiling diffusers will stay white.
High Efficiency Filters
Filters with higher MERV ratings above 10 can really clean the air. These will remove all the visible dust particles from the air and most particles done to 3 microns. The mesh is very fine and will restrict the air flow if not applied properly. A common brand on the market found in many hardware stores has a MERV 11 filter but is only 1" thick. These are design to fit the common household furnace but your furnace was not designed to use them. Higher restrictions need bigger fans to keep the same air flow or filter areas that are much larger. These filters and other 1" electro-static filters have been the cause for many, many service calls. They have a reputations as compressor killers. Reduced air flow can over heat a furnace or freeze an air conditioning coil.
If you need a MERV 11 filter, then expect it to be 4"-5" thick with large pleats. This larger surface area reduces the pressure drop of the filter and keeps the mechanical heating or cooling equipment operating as it should.
These are great filters for any one with bad allergies , asthma or reduced lung capacity These folks can really benefit from better air infiltration. The filters can be added to most forced air systems but will require some modification to the duct work to fit the larger filter frame.
The best filter on the market have a MERV rating of 17-20 , also known as HEPA filters. Air system that use HEPA filters have to be specifically design to work with that filter. There is a lot of marketing for these filters targeted to home owners that state they are 99% efficient. Stick these in the furnace and you will choke off the air. Let it run for a day or two and it will be 100% efficient and nothing will get through, including air. This add on HEPA on the right is designed to add-on to any existing forced air systems with out affecting equipment performance.
We use HEPA filter for clean rooms in electronics manufacturing , surgical rooms or labs where contamination can affect the testing. These filters are expensive and can plug up quickly. In most cases, there is a filter upstream that is MERV 7 to remove the larger particles and extend the life of the HEPA filter. For chemical contamination, we use an Activated Carbon filters which sits between the pre-filter and the HEPA filter.
Removing Virus & Germs
Disinfecting the air to kill off virus , mold and bacteria can be done with strong UV lights. These light are typically mounted inside the air plenum. An intense UV lamp is powered on when the fan is running and will sterilize the air as it passes by. Slow fan speeds work best and must not be too slow or run when the fan is off. The bulbs are very hot and should be handled carefully. When combined with a good air filter system it will be very effective. Good for people with comprised immune systems or those with extreme sensitivity to mold.