Tests of the K&N have shown that, for most two- and four-cylinder carburettors, air flow is greater when the diameter of the air filter is large compared to the height. For example, an element that is 10 inches in diameter by two inches in height will generally flow better than an element that is five inches in diameter and four inches in height. The efficiency of the air filter has an indirect impact on air flow. Generally, filters with higher MERV ratings have less airflow. By overcoming air filter restrictions, PSC motors will maintain less air flow but use the same amount of energy, while ECMs will maintain the same air flow but consume more energy.
For example, you can increase the size of the filter slot from 1 to 2 inches to fit a deeper air filter. When looking for air filters, air filters with more folds will allow greater air flow, all other things being equal. The air filter slot in your home's air conditioning system determines the depth of the air filter you can use. Since the air filters in many residential homes contribute more than half of that pressure, it's clear that air filters are responsible for much of the pressure drop in an air conditioning system. To use a deeper air filter, the air filter slot will need to be large enough to fit the filter.
MERV 11 air filters aren't too restrictive for most systems, as long as you remember to change them regularly. Since using an air filter isn't optional, you'll need to find a filter that meets both your air filtration needs and your air flow requirements. You can clearly see how the air filter reduces the total external static pressure by increasing the pressure drop. The Air Conditioning Contractors of America assumes that the pressure drop across a filter is 0.10 in. I recommend changing air filters every 1 to 2 months to maintain peak performance and energy efficiency levels.
This means that if you compare two MERV 11 air filters, the one with the most folds is likely to allow more air flow. When the air filter becomes dirty, the pressure drop in the filter will increase and cause a reduction in air flow in the system.
