Ratings index
The Five Ratings Systems That Overlap
A filter aisle has at least three numbering systems competing for the same square inch of packaging, and a portable air conditioner box carries two different capacity figures for the same machine. None of them convert into each other. Each page below takes one product and reads it through two scales at once.
- What the MERV number says vs What the MERV number does not say
MERV, and What a Higher Number Costs You
One number describes what the media catches. A second thing, which the number does not describe, is what it costs the blower.Read against Filtrete 20x25x1 MERV 12, 2-pack - What MERV says about it vs What MPR says about it
MPR and MERV Are Not the Same Scale
Two numbers on one filter, published by two different parties, measuring two different things.Read against Filtrete 20x25x1 MERV 11, 2-pack - What the listing states vs What that figure is and is not
HEPA, True HEPA, and Words That Look Like Them
One of these is a filter grade with a definition behind it. The other two are phrases printed on boxes.Read against GermGuardian FLT4825 Filter B - What the printed size says vs What the listings state as actual
Nominal Size Is a Name, Actual Size Is a Measurement
Two filters, the same printed size, and a quarter of an inch between them on every face.Read against Filterbuy 20x20x1 MERV 8 and Simply 20x20x1 MERV 8 - What the ASHRAE figure says vs What the DOE / SACC figure says
The Two BTU Numbers on One Portable AC Box
The number in the product name and the number in the specifications describe the same machine. They can differ by a third or more.Read against DREO 515S Portable AC, 12,000 BTU ASHRAE
If you would rather look a word up
Every term used across these five pages has a short entry with the same caveats attached.