Guide To Getting Your Air Filter Size Right


The performance and longevity of your heating, ventilation and air conditioning system are directly proportional to the size of the air filter you employ. It is essential to get the right size air filter because the air that flows through an inadequately sized or oversized filter is only partially filtered.

The filtration of atmospheric air is a complex, rarely-discussed topic with many unsolved concerns. The most effective pleated air filter with heat resistance is a 20×23×1 air filter. There are three methods for determining the size of the air filter needed: a) inspecting the label of the filter, b) measuring the actual filter, and c) evaluating the air intake

Inspecting the label of the filter

Examine the filter’s frame to establish its dimensions after removing it from its storage compartment. Typically, a description of the filter’s size can be found on the filter’s case. The frame displays the nominal size of the filter in bold text; nevertheless, the actual size of the filter does not correspond to the nominal size. If the measurements are not printed on the housing, the filter will need to be measured.

Measuring the air filter


To make sure, acquire a ruler and measure the current air filter’s dimensions. If the dimensions of your filter are not specified, or you are unsure of them, you can acquire a reasonable approximation by measuring the filter as follows:

  • Activate the air conditioner’s standby mode. Ensure that the air conditioner handler has been turned off before removing the filter from the furnace.
  • Check the filter’s measurements. It is necessary to measure the air filter’s size (thickness).
  • After rounding each measurement, you should be able to determine your filter’s nominal size.

If you have been purchasing furnace filters of the same size for some time, it may be time to reconsider your options. If you are uncertain whether the size you fitted is correct, measure the vehicle’s air intake.

Verify that the ventilation is functioning correctly

Determine the correct size of the air filter to purchase by measuring its opening. Here is how to verify the ventilation is functioning well;

  • To turn off the air conditioner, press the “off” button. Before repairing the handler or return vent of an air conditioner, the thermostat must always be switched off.
  • You can take measurements of your intake’s interior. Locate the exact frame dimensions or slots on the air filter and record them.
  • Rounding the number down is preferred. When determining the nominal size of your air filter, the measurement should be rounded down. The slot or frame should be between 0.25 and 0.5 inches narrower than the air intake filters.

Before acquiring a new filter, these alternatives are, respectively, consulting the dimensions of the old filter and measuring the old filter.

Where is the air filter located?


HVAC systems have filters that clean the return air. You’ll find it close to the return duct for the heating and air conditioning system. It is standard procedure to insert something into the hole that leads to the air filter. Likely, your heating, ventilation, and air-conditioning system do not have a filter. The filter may be located in the return vent of your house. You can change the air filter if you can reach it without injuring yourself.

Online purchase of air filters

It is essential, before making any purchases on the internet, to have a solid understanding of the difference between an air filter’s nominal and actual dimensions. People not familiar with these measurements typically wind up with a heating system that is not performing correctly or an air filter that is not up to par.

Nominal sizes save time

It is not uncommon for people to make purchases that are not appropriate because of a lack of familiarity with the Nominal Filter Size. For identification purposes, a filter is classified according to its nominal size. 16x20x1 These are only estimates for the filter based on the observations. The dimensions of this filter are standard; they are 15.5 millimetres by 19.5 millimetres by 0.75 millimetres. However, the brand and the manufacturer may make adjustments to these dimensions. If you are replacing an older filter or moving brands, you need to check the exact size of the new filter to guarantee that it will function as a suitable replacement for the older filter. To facilitate online filtering, the nominal size will be included in the titles of all products.

When making a replacement purchase, knowing the exact size of the filter that needs to be replaced is essential. The dimensions are length, width, and depth in the order of importance. This measurement, which is typically referred to as “actual size,” is smaller than the nominal size that is listed. If you are considering buying a filter online but need to find its dimensions, you can look in the product bulletin or description for this information. If the outer dimensions of your filter are unknown, you will need to take some measurements. You will need a filter of the appropriate size, and if your brand employs one, a piece of foam gasket matches the filter to achieve a good and secure fit.

Should the air filter be too tight?


The air filter is too large if it must be twisted, squashed, or squeezed into place to be installed. If there is less than a finger’s width of clearance around each of the four corners of the slot or frame in your air handler, your filter is too tiny. Air handlers often have spaces around the bottom. Leave a small amount of wiggle room in the slot so the filter can be withdrawn and reinserted from the HVAC unit without causing any damage. If you must force your air filter into position, you may wish to choose a new brand or a smaller custom size.

Final thoughts

It should not be necessary to force heating system filters into the correct position. If something must be pushed through the filter, it is too huge. When a filter buckles due to improper sizing, the filter’s ability to filter is significantly weakened. To facilitate filter change, their slots are designed to be somewhat smaller than the filters themselves. To meet the specifications of specific HVAC systems, filters must be manufactured in a factory. In such circumstances, a specialized lens is required.