Comments on: Understanding Filter Ratings: MERV, FPR, and MPR

By: MikeS

MikeS — Wed, 22 Dec 2021 02:25:27 +0000

In reply to RoyC. Two things can be damaged. The newer furnaces use something called and ECM motor. They work to maintain torque and or air velocity. They will actually will ramp up and work very hard to make up for the airflow that is drastically reduced by the high end/merv filters (think 3M black and purple ones). The motors will eventually burn out the electronics driving them. (Some replacements will retail for over $2200). The older PSC motors will "slip" and not deliver the airflow and will draw higher amps but tolerate the filters better. Emphasis on not delivering air very well, which leads to number two. If the airflow is severely reduced going past the evaporator coil, over time it can damage and destroy the compressor. It does so by not boiling off (or evaporating) the refrigerant in the evaporator (or A coil). This will cause liquid to enter the compressor and wash out the oil in the motor bearings causing failure. A failed compressor in a out of warranty unit usually results in a new A/C and coil. In many instances the furnace gets replaced too as to match the system. One inch high MERV filters are usually a bad idea unless sized appropriately, which is rare.

By: Bill Billiamson

Bill Billiamson — Thu, 01 Oct 2020 02:59:19 +0000

I also just bought a filter
I also just bought a filter that is rated FPR 12. I’m hoping it’s better than–or at least equivalent to– MERV 13 because I’m trying to protect my family from Covid.

By: ROBERT WEBER

ROBERT WEBER — Mon, 28 Sep 2020 01:56:32 +0000

“FPR 10 is similar in
“FPR 10 is similar in strength to MERV 20, since they are both the highest rating value”

And yet just today at Home Depot, I bought a filter that is FPR 12.

This is all very Spinal Tap.

By: RoyC

RoyC — Tue, 22 Sep 2020 14:46:50 +0000

In reply to Jim Navotney. Jim, Can you be more specific
Jim, Can you be more specific about what was "destroyed" in these systems? Did you really have to replace the whole system, or were there specific components that had to be replaced?

By: Jim Navotney

Jim Navotney — Tue, 22 Sep 2020 14:26:39 +0000

NEVER use a 1 inch high MERV
NEVER use a 1 inch high MERV filter unless you KNOW FOR CERTAIN your system was designed to handle the much greater air flow restriction they create.
I have personally replaced dozens of systems that were destroyed by using these filters.
The ONLY purpose of a furnace filter is to to keep large dust particles from clogging up the blower motor vents and the evaporator coil so a good fiberglass filter is all that is ever needed.

By: RoyC

RoyC — Mon, 08 Jun 2020 14:46:53 +0000

In reply to Ryan Shanahan. CADR is the airflow rate
CADR is the airflow rate passing through the filter multiplied by the efficiency of the filter. This combined quantity is what determines the rate of contaminant removal by the filter. Thus, if you double the airflow rate at half the filter efficiency, you would still have the same CADR. I am pretty sure that most portable air cleaner manufacturers are giving you the CADR at the highest speed which is most likely the highest CADR.

By: Robin W Boyd

Robin W Boyd — Sat, 06 Jun 2020 00:13:21 +0000

Higher speed of air does not
Higher speed of air does not always equate to more effectiveness of filtration. In fact, higher air velocity can allow more particulate to pass through filters. The best filtration occurs when the air passes through the filter media low and slow.

By: Ryan Shanahan

Ryan Shanahan — Fri, 05 Jun 2020 18:39:54 +0000

Great article. I have a
Great article. I have a ductless minisplits in my home and therefore I use standalone air filters on each floor. These units use yet another metric called "CADR" or Clean Air Delivery Rate which is independently tested by AHAM. These units provide a CADR value for how quickly the unit cleans in 3 categories: tobacco smoke, dust, and pollen in a given room size. For example my Blueair 211 units claims it has a CADR of 350 for a 540 sq ft room in all 3 categories. One thing I have yet to determine is at what speed? My assumption is on the highest of the 3 speeds the unit offers.

By: Craig Messmer

Craig Messmer — Sun, 31 May 2020 19:31:16 +0000

Thanks Allison. Nice summary.
Thanks Allison. Nice summary. Now that California title 24 requires MERV 13, I am sure 3M will start to publish the MERV rating. And just when we are getting used to MERV, along comes ISO 16890. Thanks Europe!

By: Jay Kosta

Jay Kosta — Sun, 31 May 2020 15:07:36 +0000

“make sure you can do that
“make sure you can do that without reducing air flow and possibly damaging your system.”
That’s the concern with filter choice for an existing furnace – the filter size cannot (easily) be changed. Use of a ‘high performance’ filter might require frequent filter replacement to prevent damage.