Which air filter should I be using in my home's furnace/Air Con system?
I want to get the smoke out of the air where my children live. I want lower energy bills.

This is the question for health and measured performance. What difference does it make? Apparently, having a lower pressure drop across the air filter yields more airflow and less wattage used by the motor, (hopefully a permanent magnet, electronically cummutated motor of the right size.)



At BECT, designing duct systems, the most challenging data to find is the pressure drop across filters, "Y"s, evaporator coils, register boots, start collars, ducts, plenums and grills. Once we have all that data we input it to Wrightsoft software and we can prove/know/model the performance of the airflow. Without all those we are making educated guesses, hopefully correct.

Many of the components of a duct system are difficult to find pressure drop numbers for. Knowing that, we can eliminate variables and work with what we know to be true by specifying low pressure drop components. Oversized evaporator coils, up-sized return ducts and proven air filters matched to filter boxes with lo-resistance grills fit that bill.

Below is a note from 3M to a user about their filters and how much other manufacturers' filters rate RE: MERV and pressure drop in inches of water column. This is critical data when designing a high performance duct system.

"SUMMARY: The Ultra Allergen 1500MPR (for 1 inch depth HVAC) is the LOWEST pressure at 0.15 (vs .20 for the MPR 600). So it didn't make sense for me to go for MPR 300, MPR 600 or MPR 1000.

The complete response from 3M below:

Generally speaking, for most residential HVAC systems, the filter will become restrictive when it reaches a .5 pressure drop.
All of our filter media fibers are polypropylene and polyolefin plastic which will remove particles that measure 3 to 10 microns.
Microparticle Performance Rating (MPR), MERV Ratings, and pressure drops are as follows:

Elite Extra 2400
3-10 microns - 96%
MERV 13
pressure drop .21

Elite Allergen 2200
3-10 microns - 94%
MERV 12
pressure drop .18

Maximum/Ultimate Allergen 1900
3-10 microns - 93%
MERV 12
pressure drop .16

Allergen Deep Pleat 1550 (4").
3-10 microns 97%
MERV 12
pressure drop .12

Ultra Allergen 1500
310 microns - 90%
MERV 12
pressure drop .15

Odor Reduction 1200
3-10 microns - 85%
MERV 11
pressure drop .24

Micro Allergen 1000
3-10 microns - 80%
MERV 11
pressure drop .21

Dust & Pollen 600
3-10 microns - 65%
MERV 7
pressure drop .20

Dust Reduction 300
3-10 microns -35%
MERV 6
pressure drop .20

Flat Panel
3-10 microns -5%
MERV 1
Pressure Drop .08

Pressure drop is a measure of air flow resistance. It is measured by inches of Water Column (W.C.) at 300 feet per minute (FPM).
Clean/new filters are not restrictive to air flow. Filters will become restrictive if they are not changed when needed. A filter's life is actually determined by the user's living conditions and will vary for every user. Generally speaking, we recommend changing filters approximately every 3 mo nths.
To determine when the filter needs to be change, we suggest holding it up to the light. When you cannot see light through the filter, it is ready to be changed, even if it is before 3 months.
If you are concerned about airflow, you might want to use the filter with a lower pressure drop.
If you have a high velocity furnace with high fan speed, you may need to change the filters more frequently, every 1.5 to 2 months."

Compare the above when choosing filters. Doing so could be the difference between staying below .58 watts/CFM when doing Fan Watt Draw HERS tests. First you need the airflow to pass Total Airflow HERS test, then you need low watts from the motor to pass Fan/Watt Draw.