The height and length measurements are interchangeable, so a filter measuring 11 x 21 x 1 can also appear as 21 x 11 x 1.To find the filter that best fits your filter, we recommend that you measure the dimensions of the existing filter and then look for the closest match in the nominal dimensions. A 20x20x1 air filter is actually 19-¾ x 19-¾ x ¾. This is what is known as undermining. All filters 1 and 2 are recessed by a quarter of an inch to provide a little headroom and ensure that they adjust to air return without being too large. This includes custom sizes, so a 27-8 x 23-7 x 2 (which is the strangest size we can think of) actually measures 27-¼ x 23-7 x 1-¾.
To identify the size of your air conditioner filter, it's best to remove the existing filter from its slot and examine the filter frame. Usually, the filter size is printed along the edge of the filter frame. Note that the size that appears in bold on the filter frame is the nominal size of the filter, which is likely to differ from its actual size. If the actual dimensions do not appear in small print on the filter frame, we recommend measuring the filter to check it. In this case, you'll need to round down to the nearest whole number to determine the nominal size of the air filter.
The actual size of the air filter must be between 0.25 and 0.5 smaller than the slot or frame itself. The slots in the HVAC unit are usually located near the bottom of the air controller. It's best to have a little wiggle room in the slot of the HVAC unit, so you can easily slide the filter in and out without it bending or breaking. This includes custom sizes, so if you need a specific size for your system, you can opt for a custom-sized air filter with a slightly smaller actual size. Central air return ventilation grilles are usually located on the hallway ceiling or on the hallway wall of your house. If the return ventilation grille is on the roof, you can opt for a filter that has a slightly larger actual size, so that it doesn't fall on you when you open the ventilation grille.
When buying a custom-sized air filter, it's important to remember that its actual size must be between 0.25 and 0.5 smaller than its nominal value. The easiest way to determine this is to round down to the nearest whole number when measuring your air filter. Whole house filters usually go to an air controller, which is usually found next to the HVAC system itself. If you're looking for a store near you that sells custom-sized air filters, you might have a hard time getting lucky. There are literally thousands of sizes of air filters, and HVAC manufacturers are encouraged to make it as complicated as possible, so you don't have to pay for expensive replacements. For example, Home Depot primarily sells Honeywell brand air filters, while ACE Hardware primarily sells Filtrete. Do not stack several smaller air filters one on top of the other to place them on a larger air controller.
To ensure that your next purchase is an accurate fit for your system, measure both sides of your existing air filter with a measuring tape.HVAC service companies typically offer air filter replacement services in addition to system repair and unit installation services. Accordion air filters also exist and, as it sounds, they are shaped like accordions. The nominal dimensions are rounded to the nearest measurement and are usually what most air filters are sold by. To ensure that your next purchase is an accurate fit for your system, measure both sides of your existing air filter with a measuring tape.