Most air filters have two sets of dimensions: actual and nominal. The actual dimensions of your filter are the measurements you take yourself of the height, length, and width of your filter. Nominal dimensions are rounded off to the nearest 1" measurement and are the dimensions that most air filters are sold under. For example, if your air filter measures 10 ½“ x 20 ¾” x 1¼”, the nominal dimensions will typically be 11” x 21“ x 1”.
To find the best fit for your filter, we recommend measuring the dimensions of your existing filter and then looking for the closest match in nominal dimensions. Height and length measurements are interchangeable, so a filter with measurements of 11” x 21” x 1” may also be listed as 21” x 11” x 1”.
Your filter should fit snugly without having to be forced into place. Trying to fit a filter that is too large into the required space can cause the filter to tear or buckle and result in a loss of efficiency. If you notice air leakage around the sides of the filter after installation, you may use gasket tape around the edges of the filter to create a tighter fit.
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