The actual size is the exact size of an air filter. If you measure the filter with a tape measure, you get the actual size. The actual size of an air filter is usually ¼ to ½ inch smaller than its nominal size. To convert actual to nominal size, measure the filter and round each dimension to the nearest inch.
All filters have two different sizes. All filters have a real size and then a nominal size. The actual size is the exact dimensions without rounding, while the nominal size is the rounded dimensions of the filter. This means that in 1 and 2 air filters, the nominal size does not include the bottom cut and the actual size does include the bottom cut.
In whole-house filters, the nominal size is the rounded size, and the actual size is only the non-rounded one. From sizes to types, qualities and more, here's everything you might need to know about air filters. It is important to note that there is no need for an airtight seal between the frame and the air filter. Another caveat is that, given the relationships between suppliers, they could be encouraged to sell more than certain types or brands of air filters.
That's why it's necessary for those of you who need a whole house filter to know the exact filter size you need. In this case, you'll want to round down to the nearest whole number to determine the nominal air filter size. HVAC service companies typically offer air filter replacement services in addition to system repair and unit installation services. The length, width and depth of a filter are printed in small quantities along the filter frame on the cardboard border of a Filter King brand filter.
These numbers refer to the standard size of your home's return ventilation grilles, responsible for controlling the movement of air to and from your HVAC unit. Most air conditioning and HVAC units use standard size filters, but some require the purchase and installation of a custom-sized air filter.