if you have the space you could go with a 2" Filter it should give you
more surface are and more stiffness you can check the airflow coming
off the vents with the filter on and off

Robert Gammon wrote:

I got to reading up on this topic as research fora new house that I
want to start building soon.

I read that most furnace fans are only capable of driving about 0.5
in water of pressure. AC coils take 0.2 to 0.3 in of water pressure
drop, ducts take another 0.1 to 0.2 in of pressure and then nothing
is left for the furnace filter. That's why the cheapest of all
filters are generally included on furnaces.

To top it off, furnace installers often do not read the specs for the
units that they are installing.

We had our HVAC replaced about 3 years ago with a 12 SEER,80% gas
combo. At the time, I insisted that the existing 20x20x1 furnace
filter be replaced with a 20x25x1 model ($50 part,$50 filter(20x25x5
Honeywell), $200 labor).

As I have done this research, I have looked at the face of the $6
filter I have installed in the unit presently. It is heavily bowed
when the furnace is operating (but makes less noise than the old
furnace with a 20x20x1 filter in it). So much bow is there that I
worry about the filter collapsing. So far, so good, none have
collapsed.

However, reading the specs NOW, its clear that the HVAC installers
were not reading the manual. In the mfg's manual, it clearly says for
this size fan, operating at roughly 1200 CFM (can operate as high as
1328 with no load),the unit needs not 400sq inches that I had, not
480 sq inches that I now have, but 576 inches (24x24). This extra
back pressure on the fan is ROBBING performance, and costing me
money. It is at least a 10% drop in air flow.

Cheap solution is to revert to 99 cent fiberglass and change them
every few weeks. I want to think of something better than this.
BTW increasing the size of the filter to 20x30 is not do able as the
structural supports for the furnace are in the way. Any ideas are
welcome.