Air filters for your home air-conditioning unit, also known as A/C filters or furnace filters, are used to remove impurities from the air entering the air-conditioning unit. Removing these impurities (dust, pollen, smoke, etc.) keeps the coils and heat exchangers inside the A/C unit clean and allows the unit to operate more efficiently. The more efficient the unit operates, the less energy it requires to condition the air, and the less electricity it uses!
As you might figure, if the filter cleans the air going into the unit, it is also cleaning the air that the unit produces for your home. As air quality has grown in importance, filters have become more important. Today a filter is chosen as much for its ability to purify the air you breathe as it is for the protection value it offers your air-conditioning unit.
There are two basic categories of disposable filters:
Flat Panel - These are produced using either fiberglass or polyester filtering media. Polyester would be considered the superior of the two materials. There are other materials such as hogs' hair and coconut fiber but for the most part, these have been replaced by manmade products. Generally speaking, flat panel filters are the basic product for filtration. Flat panels are economical but need to be replaced frequently.
Extended Surface (Pleated Filters) - These filters are made of an advanced material that is either a cotton polyester blend or an all synthetic material. Looking at the filter, you will immediately be able to identify it as a pleated filter as the media is pleated and looks similar to an accordion. This pleating allows for more filtration media to be placed within the same frame. More filter media means more area to collect particulates and a greater capacity for the filter, resulting in fewer filter changes.
There are 3 basic criteria to consider when picking a filter:
Size - Your unit is designed for a particular size of filter and that is what is required. Usually, the size will be printed on the filter you are replacing. If you cannot find the size printed on the filter, you can measure it to find the size. See "Finding the Right Filter Size" below.
Cost - Filters sell for different amounts but that is only part of the story because filters have different capacities. Normally, a flat panel filter will be cheaper to purchase than an extended surface (pleated) filter. However, the pleated filter can hold more particulate than the flat panel, so it does not have to be changed as often and in fact can last up to three times longer. So even though the flat panel is less expensive to purchase, you may have to buy as many as two additional filters to last as long as the pleated filter.
MERV - MERV stands for Minimum Efficiency Reporting Value. This is a standard developed by the industry to compare filters. The rating goes from 1 to 16 with 16 being the best and 1 being the least efficient. It follows that the higher the MERV number, the higher the efficiency and the better the filter. Any filter rated above 12 is so restrictive that it is not practical for residential use. A MERV rating of 7 to 12 will offer excellent air filtering qualities for residential units.
Measure the filter - If the filter in the unit fits, purchase the same size. The size is usually printed on the side of the filter. If there is no size printed on the filter, measure the length, width and depth of the filter. Remember that the measurements you take are exact, but filters are measured in nominal sizes.* You can convert your measurements to nominal by rounding each number up to the nearest inch, or when you order, tell the filter specialist your measurements are exact.
Measure the opening - If there is no filter in the unit, or you feel the filter is the wrong size, measure the length, width and depth of the opening where the filter fits. When speaking to the sales representative about a filter measured in this manner, be sure to tell them that you have "exact" dimensions for either the filter or the opening. This will ensure the filter you purchase will fit the way you planned.
* Note: Filters are in nominal sizes, similar to lumber. A filter sold as a 24" x 24" x 1" filter will measure 23 1/2" x 23 1/2" x 3/4".
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