Last edit: 10/08/15

Buyer's Guide to Winix Air Purifier Replacement Filters

If you are already a seasoned Winix user, you can skip through the text by scanning for your highlighted Winix model number.

Some air purifier lines don't really need a filter buyer's guide, but I wouldn't say that about Winix, where numerous buyer reviews express frustration and misunderstanding concerning replacement filters.

Korean air purifier maker Winix has prospered in the US market by offering good value and superior quality relative to Chinese competitors.

To remain competitive on price, Winix wisely cuts features (as opposed to cutting quality), and evolved a dual feature strategy for the product line.

Each of three chassis/bay sizes, Size 17, Size 21, and Size 25, are offered as economy models and separately as premium ("ultimate") products.

The primary difference is the filter trains.

Economy two-filter setups, which I will refer to as "value" packages, leave substantial empty space in the filter bay, while Ultimate Cassette systems fill it with a plastic frame ("filter cassette"), add a lot more carbon, some additional antimicrobial treatment (not recommended here), and a permanent washable fiberglass prefilter screen.

The issue for me is the substantial price differential Winix charges for the Ultimate packages, when laser particle counter testing has demonstrated very good particulate removal using their value filter train (with tape-sealed HEPA edges and additional prefilter material added).

Winix filters are NOT interchangeable between value and Ultimate packages!

winix cassette filters

Ultimate Cassette systems, photo at right, will NOT accept value filters without removal of the cassette.

Numerous users have tried to force the slightly larger value HEPA into the Ultimate Cassette frame, I guess I need to add "NOT recommended."

Some user reviews say they have attempted to cut down the value HEPA to fit the tray, a huge NO-NO!

To retain the Ultimate package, users MUST buy the whole bundle every time.

Again, there are NO individual replacement filters available for the Ultimate packages.

Downgrades are permissible, but Ultimate Cassette users can NOT substitute the cheaper filters without discarding the screen prefilter and cassette tray, and accepting the reduced odor capacity of the value package prefilters.

OK, maybe I repeated that enough times.

Of course, value system owners could theoretically upgrade to $120 cassette systems for their $200 air cleaner, maybe a few do.

Winix value filters, photo left below, are sold as bundles of one HEPA and four antimicrobial prefilters, forcing users who may not have odor issues to buy prefilters. winix value filters

Four-packs of prefilters are available, but are unfavorably priced.

Winix, despite great products and undeniable success, has difficulty communicating effectively with American consumers, their instructions tend to be cryptic.

Ultimate Cassette systems just slide in to replace the old tray, but value set-ups MUST have the HEPA in back with one prefilter fitting into a depression and lip of the HEPA, in the front ("prefilter").

Many users are installing the prefilter in back.

One consumer review admitted to installing all 4 prefilters at the same time (a year's supply when changed out every 90 days, yes, they will fit).

Winix smoothed entry into the US market with a series of re-branded marketing deals.

Winix standard-sized chassis and filter bays were sold, with different front covers, as Kenmore, Electrolux, and now Fellowes air purifiers.

Cross-fit filter applications are common, see "Fellowes" below.

Very expensive Ultimate replacement filters, and pricey value filters, tarnish the economy image, with many filter buyers searching for alternatives.

I find the nearly-empty filter bays of the Winix value models ideal for experimenting with performance enhancing/money-saving extra prefilter combos.

Many Winix owners were confused by the company's dual filter descriptors - size ("Size 21"), which refers to the filter bay size, and a six-digit part number ("115115") which identified the specific filter.

While Winix has stopped using the 6-digit part numbers, they are still used by many vendors.

But now Winix identifies filters by model series names: FresHome, PlasmaWave, Signature, and Ultimate Pet.

FresHome and PlasmaWave Replacement Filters

FresHome and PlasmaWave - Size 21, #115115, Value Filter Set

FresHome Series and PlasmaWave models use value filter trains, a HEPA with a single prefilter.

This filter set, sometimes referred to as Model 21HC4, fits all Size 21 filter bays, but is specifically sold for:

FresHome P300 #115115, Winix Size 21, MSRP $79.99

PlasmaWave 5300 #115115, Winix Size 21, MSRP $79.99

PlasmaWave 6300 #115115, Winix Size 21, MSRP $79.99

Also fits Winix air cleaner models 9000, 9500 (must scrap cassette tray), 5000 (remove cassette), 5500, 5000B, and Electrolux EL491A.

This HEPA filter measures 12 5/8 inches wide, by 16 3/8 inches tall by 1 1/4 inches deep, just a bit too big to squeeze into cassette trays.

The 115115 Size 21 package has one true-HEPA with 4 odor prefilters, and sells at Amazon for $54 to $67.

Winix 115115 Size 21 True HEPA Plus 4 Prefilters at

Or for MSRP.

PlasmaWave 5500 #115122, Size 21, True-HEPA Filter (no prefilters), MSRP $79.99.

This is the "washable" HEPA, something I said would never work, part of the "permanent HEPA" marketing fad of a few years back.

User reviews say this filter begins to deteriorate after a couple washes.

PlasmaWave 5500 owners could install the standard Size 21 value package, #115115 (above), dropping the washable HEPA experiment and its $50 higher price tag.

The washable HEPA filter is available for about $71 at amazon;

Winix 115122 Size 21 Washable HEPA at

And at

Winix Size 21 Carbon Prefilters 4-Pack

PlasmaWave 5500, and other Size 21 users who need more that four prefilters for each HEPA (smokers, pets, etc.) can buy the #115119, Size 21, carbon filter 4-pack.

At amazon, price is around $57;

Winix Size 21 Odor Control Carbon Pre-Filters - Set of 4 at

Fellowes Filter Swap Saves Winix Size 21 Users Real Money

Fellowes HF-300 HEPA, for a re-branded Winix purifier (AP-300), (Fellowes filter part number 9370101), is exactly the same as Winix size 21 HEPA, part number 115115.

I recently ordered the Fellowes filter, which ships WITHOUT the 4 prefilters, and installed it in my Winix 5300.

The Fellowes version cannot be distinguished from the Winix #115115 HEPA, and tested well with my laser counter.

The "Fellowes" version (HEPA filter only) goes for $23 to $30 at amazon:

Fellowes HF-300 True HEPA Filter at

FresHome P450, #113250, Winix Size 25, HEPA plus 4 prefilters

The Size 25 value replacement filter set fits FresHome P450, and can be used to downgrade the Winix Signature U450 to a value filter train by discarding the cassette tray and permanent screen prefilter.

About $80 at

Winix #113250, Size 25, Replacement Filter Set at

And around $90 at

Winix FresHome P150, #113050, Size 17, Filter Set

FresHome P150 uses Winix #113050, Size 17, HEPA and 4 prefilters, MSRP $59.99.

Size 17 also fits Winix 9300 and 9000S.

This filter set, sometimes referred to as "17HC4," goes for around $60 at;

Winix Size 17 Replacement Filter Set #113050 at

Or for MSRP.

A user experiment, reputable but not personally verified by me, suggests a successful match of Fellowes HF-230 HEPA and Winix Size 17 chassis.

From a user email:

"I have both the Winix P-150 air purifier and the Fellowes HF-230 replacement air filter with me and they are a perfect fit: the (Winix and Fellowes) filters are indistinguishable from each other."

Amazon sells the Fellowes HF-230 (HEPA only) for around $29.99;

Fellowes HF-230 True HEPA Filter at

Signature Series and Ultimate Pet Series Filters

Winix Signature Series and Ultimate Pet Series ship with Ultimate Cassette filter trains.

Within the last few years, Winix made a few minor changes, tabs and indentations, to the Ultimate Cassettes and changed the color from gray to black.

Signature U300 uses #114190, Size 21

Signature U300 uses #114190, Size 21, Long Life Washable True-HEPA Filter, MSRP $119.99.

114190 is a full cassette with added antimicrobial treatments, extra carbon with zeolite, and a washable permanent prefilter.

This filter system is intended to be replaced annually as a unit.

Users of other Size 21 models (5300, 5500, 6300, 5000, 9000, 9500, and P300) can install this Ultimate filter system as an upgrade. has this for $100-$119, with frequent fluctuations.

Winix owners can browse the current price at amazon;

Winix #114190, Size 21 Ultimate Washable Filter Cassette at

Or try

Signature U450 takes #114290, Size 25, MSRP $139.99

114290 is also a complete one-decision annual filter package.

Amazon price is $119.99.

The amazon vendor is, a highly-reputable allergy store.

Winix 114290 Size 25 Washable Ultimate Filter Cartridge at

Or at winixamerica for MSRP.

Winix 9300, 119010, Size 17, Ultimate Pet Cassette, MSRP $89.99

Price at Amazon is close to $100;

Winix 119010, Size 17, Ultimate Replacement Filter at

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