Mechanical filters come in just about every size imaginable – typically rectangular in size but they do come in squares. Mechanical filters are also available in different thickness. You can even get this type of filter in rolls and cut your own to the size needed.

Mechanical filters remove the dust by capturing it on the filter media as the air is pulled across the filter incorporating three processes known as impingement, interception and straining.

When selecting a mechanical air filter, there are four things to consider.
Efficiency - Pressure drop - Atmospheric dust holding capacity and the capacity.

The efficiency is your most important of the four; it is the filters ability to remove the most dust particles.

Pressure drop across the air filter, this is too important because the higher the resistance the greater the energy required to overcome it...you actually remove more dust particles with higher velocity or “faster” air across the filter, when your filter is of the denser kind it may seem like it’s a better filter but considering the processes of impingement, interception and straining and how they work, the lowest resistance in air filters is preferred.

Atmospheric dust holding capacity – the amount of atmospheric dust the filter can hold before it’s considered full. A filter with the highest atmospheric dust holding capacity will have the longest life and will need to be serviced less frequent.

The capacity is the amount of air that a filter can handle. This means the filter can handle x amount of air measured in (CFM) cubic feet per minute, or the x amount of air can pass through the filter. If you change the amount of air the filter can handle outside the design of the filter can affect the other filters performance such as pressure drop, dust-holding capacity.

The wrong filter or filter that has not been maintained or changed can cause problems with your heating and air conditioning system in general. When if you restrict air across the AC coils or heat exchanger you affect the design temperatures to a point that the furnace or AC may not work properly or safe? If you restrict air across the heat exchanger when the furnace is heating, you risk the high limit failure and your furnace should shut down? If you restrict air across the AC coil as the AC unit is running, you risk freezing up the coil.