Evaluating HVAC Filters – GreenBuildingAdvisor

My fairly tight house was set up so that when the kitchen exhaust hood is turned on, a damper opens and lets in unfiltered, unconditioned ouside air.  The interior grill where the outside air enters the house was getting quite dirty, so I replaced the grill with a 2″ filter grill and installed a cheap 2″ filter.  I’m astounded that after a few months (kitchen hood runs max 1 hour/week total) the filter is absolutely FILTHY.  Thus, I’ve determined filtration of this makeup air is essential.

So now I’m trying to determine which filter to use.  The goal is the best combination of airflow & filtration. 

a. I’d like to ensure this makeup air system (however flawed) remains the point of least resistance when the kitchen hood is on, so I think a MERV 8 may be as high as I want to go with filtration. Does this seem correct?

b. The kitchen hood is 400 cfm max, so I think I only need to be concerned about resistance up to 400 cfm, but that is 400 cfm across a 2″ filter of a different area than in the test reports, so how do I calculate the adjustment?

Below is data from test reports from 2 different filter mfgs.  for MERV 8 filters.  Interestingly, both mfgs filters were tested by the same testing company, so the report format is identical.

How does one interpret which one provides the best combo of air flow & filtration? They don’t test with the same size filter, just the same MERV rating and face velocity.

Mfg A Merv 8 filter has fewer pleats/inch and catches fewer particles but lower initial resistance…

Mfg B Merv 8 filter has more pleats/inch and catches a higher percentage of particles but higher initial resistance…

Mfg A:

Nominal Dimensions (H x W x D) 24″ x 24″ x 1″

Pocket / Pleat Quantity 24 Pleats

Media Type B1.6

Est. Gross Media Area 7.04Ft

Adhesive Type N/A

Test Results

Airflow Rate (CFM) 1180

Nominal Face Velocity (fpm) 295

Initial Resistance (in WG) 0.15

E1 (%) Initial Efficiency 0.30 ­ 1.0 um 2

E2 (%) Initial Efficiency 1.0 ­3.0 um 34

E3 (%) Initial Efficiency 3.0 ­ 10.0 um 70

Mfg B:

Nominal Dimensions (H x W x D)20″ x 20″ x 1″

Pocket / Pleat Quantity 22 Pleats

Media Type Synthetic

Est. Gross Media Area 5.38 Ft²

Adhesive Type N A

Test Results

Airflow Rate (CFM) 819

Nominal Face Velocity (fpm) 295

Initial Resistance (in WG) 0.18

E1 (%) Initial Efficiency 0.30 ­ 1.0 um 5

E2 (%) Initial Efficiency 1.0 ­3.0 um 43

E3 (%) Initial Efficiency 3.0 ­ 10.0 um 83