When it comes to furnace, AC, and HVAC filters, understanding the distinction between nominal and actual sizes is crucial for selecting the correct filter for your system. Here's a straightforward explanation:
Nominal Size: This is the rounded, easy-to-remember size that manufacturers and retailers use to label filters. It simplifies the search and comparison process. For example, a filter labeled as "20x25x1" uses nominal measurements, rounding up to the nearest whole number to make identification and selection straightforward for consumers.
Actual Size: Contrary to the nominal size, the actual size represents the filter's precise measurements. Using the same example, a "20x25x1" nominal filter might have actual dimensions of approximately "19 ½ inches by 24 ½ inches by ¾ inch." These dimensions are the true, exact size of the filter when measured with a tape measure, and they are typically slightly smaller than the nominal dimensions to ensure the filter fits snugly into the HVAC unit without forcing it.
In summary, when purchasing filters, it’s important to be aware of both the nominal and actual sizes. The nominal size helps you quickly identify the filter you need, while the actual size is critical for ensuring the filter fits perfectly in your system. Always double-check the specifications of your HVAC system and the filter you are considering to ensure compatibility.