"Honeywell" air cleaners have around $400 million in sales worldwide, a top-selling brand.
Two results of this popularity are:
1.) Genuine Honeywell Original Equipment Manufacturer (OEM) replacement filters are widely available, and
2.) a brisk aftermarket flourishes, with knockoff-generic filters sometimes represented as "Honeywell."
Kaz once used a numbering scheme (i.e. "38002"), for hundreds of different replacement filters, which was easily preempted by aftermarket vendors.
Amidst an industry downturn, Honeywells were switched to a modular filter plan which standardized nomenclature and packaging, and reduced the total number of different filters sold.
This also made the counterfeits, which still sell well, easier for shoppers to spot.
Most genuine Honeywell OEM filters now feature distinctive red/white packaging and the prefix "HRF-" in the model number.
Generics save money, but can have wider variations in quality and multiple revolving-door vendors, than genuine OEM replacements.
But, in my opinion, the quality of genuine Honeywell OEM filters and pre-filters has been slipping of late, narrowing the gap with the uppermost generics.
Prefilters are a fat cash cow, and Kaz and generic vendors are making the most of the opportunity.
The best way to be sure you're getting real OEM pre-filters is to buy from the kaz.com website.
Amazon.com offers lower prices, and wider selection including generic alternatives, but also features many third party vendors.
HRF-AP1 is Honeywell's "Universal" Carbon Air Purifier Replacement Pre-Filter, this replaces old pre-filter numbers 38002, 32002, 33002, 34002 and 35002.
Also called "Filter Type A."
HRF-AP1 is a 15.75 by 45.5 inch cut-to-fit carbon-impregnated prefilter sheet for many Honeywell purifiers.
163 customer reviews of the AP1 prefilter at amazon.com, where this prefilter is a top seller, average 4 stars.
These sheet materials can also be used for almost any brand air purifier with filter bay less than 15.75 inches wide.
The AP1 replacement pre-filter fits most round Honeywell Enviracaire HEPA air cleaners, here is the list:
10500, 11502, 11520, 11526, 11528,
12500, 12520, 12526, 12528,
13350, 13500, 13520, 13526, 13528, 13530, 13531, 13533,
17000, 17005, 17006, 17007HD, 17007-HD, 17008, 17009, 17200, 17205, 17205CST, 17210, 17352, 17400, 17440, 17450,
18150, 18153, 18155, 18225,
40100, 40200, 40201, 41200,
50100, 50101, 50150, 50151, 50152, 50200, 50201, 50250, 50251, 50255HD, 50255-HD, 50300,
51130, 51500, 52000, 52500, 53000, 53001,
60500, 61200, 61500, 62500, 63200, 63500, 64200, 64500,
HPA-094, HPA-100, HPA-104, HPA-200, HPA-204, HPA-300, and HZ680C.
The genuine OEM kit has perforations and templates, allowing users to cut out 1 to 8 pre filters, depending on which Honeywell they own.
17000 series owners can get two prefilters, but 50250 folks get only one with about 1/3 waste, cutting the HRF-AP1.
Many users find the old prefilter the best template.
HRF-K2 reduces odors using potassium permanganate calcite, a bit more expensive than plain activated carbon.
HFD-120-Q owners must cut this filter cut to fit.
Some user reviews say HRF-K2's are too narrow to span the air intake.
$17 at amazon, with higher prices, to $35, found across the web.
Buyers who want to save a few bucks could choose the "GE" 48 by 16 inch blanket wrap recommended above and cut it to make multiple prefilters.
At the official kaz website, price is $13.99 plus shipping.