The April-Aire filters have a high MERV, 12 as I recall. They have
MUCH less restriction to air flow than the one inch pleateds. Up to
2.5 tons, the April-Aire filters are about the same pressure drop or
less as a properly sized fiberglass filter. The one-inch pleated
filters have about 2.5 times the pressure drop of a properly sized (or
same sized) fiberglass filter. This is according to my own testing
with an air flow hood and digital manometers and magnahelic gauges. If
you put a carbon filter in the 1" slot, plus have the Aprilaire filter,
your pressure drop will go sky high again. Typically, a 1" pleated
filter will drop air flow 10% to 20% vs. a standard fiberglass filter.
If you want all that filtration, have someonme measure your air flow
with a flow hood before you install the filters. If you have less than
400 CFM/ton, stick to a fiberglass filter OR upgrade to a variable
speed blower OR replace your duct system. Low air flow will reduce
your system capacity efficiency and capacity. It can also damage your
compressor.

Stretch