Heating, Air Conditioning, Fridge, HVAC/furnace filters


I am trying to find out about the pressure drop  posted by the filter manufacturer. For instance: Filtrete rates their 1000 filter at a PD of 0.21" w.c.  This is the same rating that they use for all Filtrete 1000. Whether it is a 12"x12"x1" or a 20"x30"x1" filter. Common sense tells us that the overall PD of the filter has bearing on it's size. A 20"x30"x1" is going to be less restrictive than a 12"x12"x1" filter.  Therefore, it stands to reason, that the PD has to do with a specific square measurement of the surface area. i.e. square foot, square meter, square what???  I have contacted  several filter manufacturers and the people that answer the email or phone do not know and are unable to get the information.

The pressure drop though the filter is the same no matter the size of the filter at the recommended max flow rate (FPM).  The slower the air flow the less the PD will be.  To determine FPM, take CFM and divide by the SQ FT of the filter.  



Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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