Q: I am installing a new unit and AC air return. What is the correct size of the return for a 4ton ac using a Dust Fighter™ 95. My chase to the attic coil is 24 x24 and 13’ long.(9’ vertical and  4’ horizontal to the coil in the attic)……….the return air is 24 x 30 and I want to use a  Dust Fighter™ 95 filter MERV 8 should I make the return air larger.  I cannot change the size of the chase thanks in advance for the help

It is our opinion that this a very restrictive filter to put in the wall that far away from the blower. The further away the filter is from the blower and the denser it is, the more it can affect the static pressure on the system. You also need to make sure that furnace can provide enough airflow to compensate for the filter restriction.  With this type of filter, you may need to double the return size and grill to compensate.

If possible, the best filtration application is one that is installed as close to the furnace return as possible.