John Gilmer wrote:
Hepa filters put a huge strain on a blower as the pores are so small,
never do this one without an experts advice on capacity.


If the filter is, say, 3" thick and had many, many pleats then the extra
area can compensate for the extra resistance of the HEPA filter medium.

To me, that's the way to go. Rather than a high maintenance electrostatic
filter which, typically, requires 6" of space in the direction of flow, get
a pleated HEPA filter that fits in the same space.



The issue with HEPA filters that the poster complained about is that in
order to get the 99.97% entrapment of 0.3 micron particles and larger
takes large amount of fan power. Furnace fans cannot do this by
themselves. To move 1500 CFM (typical flow number for 4 ton AC units)
through a typical HEPA filter requires almost 1HP of fan power. Air
handler fans are woefully inadequate to this task as a typical air
handler fan only has a tiny budget left for filter resistance.i.e. MERV7
OVERLOADS THE FAN!!!

www.pureairsystems.com sells whole house HEPA filters that do not load
the air handler fan as they have an internal fan that blows at the same
CFM rating of the air handler .

The only advantage that a 4" or 6"pleated filter has over a 1"or 2"
pleated filter is a longer lifetime before they start to really bog down
the air handler fan.

One of these days people will start to realize that the furnace filter
is there to protect the equipment, not the occupants.

When you want to protect the occupants, the HP rating of the air handler
fan must increase to compensate, OR we add a fan on the other side of
the filter (as the pureairsystems folks have done) to PUSH air thru the
filter, reducing the load on the air handler.

Some manufacturers of heat pumps are starting to recognize the issue and
now offer motor upgrades on some models that doubles the HP rating and
gives the fan the power needed for MERV 11 and MERV 12 filters to be used.