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 3/4”, the nominal dimensions will typically be 11” x 21“ x 1”.
Here at pureairfiltersdirect.com, we manufacture your filters to the exact measurements you provide to us, we find this to be the best fit for your air conditioner, we recommend measuring the dimensions of your existing filter. 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 or too small into the required space can cause the filter to tear or buckle and result in a loss of efficiency. This also may cause the filter to blow-up into your air handler or ducting and cause damage . If you notice air leakage (a whistling sound) around the sides of the filter after installation, you may use gasket tape around the edges of the filter to create a tighter fit.