Quest and Anden Filters: Sizes, Ratings and Replacement Timing

Quest filters by model

Start from the model number on the data plate, not the pint rating on the front. Pint ratings repeat across generations and voltages; model numbers do not. A Quest 225 built as a Dual takes a different filter from a Quest 225 built as a Next Gen, and the two are not interchangeable.

Two size columns, because Quest lists most of its media at a rounded catalogue size while the filter itself can measure smaller.⁵ Where the second column is filled in, that is what a tape measure reads on the part. Where it says the same as listed, one number covers both. The next section explains why the convention exists.

Two rows there deserve a word. The Dual line and the Next Gen line both include a 155, a 205 and a 225, and they take different filters — 16 × 20 × 2 for the Dual, 18 × 18 × 2 for the Next Gen. The units currently listed on this site are all Next Gen. If your data plate reads 4031490, 4033060 or 4035400, you have a Dual and you want the 16 × 20 × 2. If it reads 4046120, 4046110 or 4046100, you want the 18 × 18 × 2.

The other one is the pair of 16 × 20 × 2 rows. Those are the same slot in the same units, offered at two grades. Running the MERV 13 in a Dual is a straight upgrade, not a different part.

Two units in that table run a coarse pre-filter ahead of the main media — the 70 Pint and the H5. A pre-filter is a sacrificial layer that takes the lint and the grit so the graded filter behind it only handles what actually needs stopping. Where one is fitted, it is the part that should be changed most often.

Anden filters by model

Anden numbers its filters in a four-digit series that maps cleanly onto the model, which makes this side simpler. Every current Anden dehumidifier uses MERV 11 media, so there is no rating to weigh up — only the right part number for the machine in front of you.

One size column here rather than two, and that is not an omission. Anden publishes a single figure per filter, and those figures already read as measurements rather than rounded catalogue sizes⁸ — 8 × 11.75, 11.88 × 13.5, 29.5 × 31.5 × 1.75. Nobody rounds a filter up to 11.88 inches. There is no second number to reconcile because Anden never published a rounded one.

One coincidence worth flagging before it costs somebody a week. The Anden 5813 and the Quest 335 filter are both 20 × 22 × 2. They are not interchangeable — the frames, the media depth tolerance and the retention hardware differ, and neither manufacturer lists the other's unit. Same outside dimensions is not the same part.

Why your filter has two sizes

Pull a filter out of a Quest Next Gen 225 and put a tape on it and you will get 17.5 by 17.5 by 1.75. Look it up and Quest calls it an 18 × 18 × 2. Neither number is a mistake. Pleated filters have been sold this way since long before any of these units existed.

The nominal size is the catalogue size, rounded up to whole inches. The actual size is what the filter measures, and it runs roughly half an inch under in the two face dimensions and a quarter under in depth. The gap exists so the filter slides into a frame built to the nominal opening without binding.

That convention is why the Quest table needs two columns and the Anden table does not. Quest lists most of its media at the rounded number; Anden lists what the part measures. Neither brand is being careless — they are answering different questions, and a grower holding a tape measure only ever gets one of the two answers.

Three practical consequences follow. A filter listed as 16 × 20 × 2 and one listed as 19.5 × 15.5 × 1.75 can be the identical part, and on this site they are. Searching a measured dimension will often turn up nothing, because most listings carry the nominal number. And the face dimensions get printed in either sequence depending on who wrote the label — Quest lists its smallest Next Gen media as 11 × 9 × 1, while the same part under the Santa Fe name reads 9 × 11 × 1.

That last one is not a typo either. Quest, Santa Fe and Ultra-Aire are all Therma-Stor brands and they share part numbers across the range. If two listings show the same part number, they are the same filter regardless of which brand is on the box or which way round the dimensions are printed. The part number is the thing to trust.

What MERV actually measures

MERV stands for Minimum Efficiency Reporting Value. The EPA describes it as a filter's ability to capture particles between 0.3 and 10 microns, on a scale of 1 to 16, derived from a test method developed by ASHRAE.¹ The word doing the work in that sentence is minimum.

A MERV number is not one percentage. It is a floor across three particle size bands, and a filter has to clear all three to earn the rating. Here is what the EPA publishes for the three ratings that show up on these units.¹

Read across the middle band and the reason MERV 13 gets specified in cultivation spaces becomes obvious. Most fungal spores that matter indoors land between one and three microns. A MERV 8 is allowed to pass eighty percent of them; a MERV 13 has to stop eighty-five percent. That is not a marginal difference in a sealed room being turned over every few months.

Both manufacturers also publish their own summary figures. Quest describes its MERV 13 media as twenty percent more effective than MERV 11 and sixty-five percent more effective than MERV 8.⁵ Anden says its MERV 11 traps ninety-five percent of pollutants.⁷ Those are the brands' comparisons rather than standard measurements, and neither maps onto the banded numbers above — which is worth knowing when two spec sheets seem to disagree. The banded figures are the ones tied to the test.

Where HEPA sits

HEPA is not a MERV rating at all, which is why the Quest H5 filter is described differently from everything else in the first table. The EPA defines a HEPA filter as removing at least 99.97% of particles at 0.3 microns, and adds the detail most specification sheets leave out: 0.3 microns is the most penetrating particle size, the hardest case. Particles larger and smaller than that are caught at higher efficiency, not lower.² A HEPA filter is not a wall with 0.3 micron holes in it.

That efficiency costs airflow, which is why the H5 runs a MERV 8 pre-filter in front of the HEPA. The pre-filter takes the lint and the coarse dust so the expensive media only sees what actually needs it. Change the pre-filter on schedule and the HEPA behind it lasts considerably longer.

When to replace it

Both manufacturers publish an interval, and they do not say the same thing. That is useful rather than confusing, because the two answers bracket the sensible range and the reasoning behind each is stated plainly.

Quest's manuals for the 335 and the 506 both say the filter should be checked every six months. The 335 manual recommends changing it at least every six months.³ The 506 manual goes further and addresses growers directly: change the filter every three to six months, or in growing environments, at least with every grow cycle.⁴

Anden is tighter. Its published guidance is to replace filters every twelve weeks or at the end of a harvest,⁶ and its grower guide gives the reason — changing media when you turn the room over avoids carrying contamination from one cycle into the next.⁷ A filter that has spent ten weeks collecting spores is a reservoir sitting in the airstream.

So: twelve weeks to six months depending on the brand and the room, and every manufacturer statement converges on the same practical rule. Change filters when you turn the room over, and you will never be far wrong. Rooms running dusty media, heavy defoliation or high traffic want the short end of that range.

What running it too long actually costs

Quest is unusually direct about this, and the same sentence appears in the 335 and 506 manuals word for word.^{3, 4}

Do not operate the unit without the filter or with a less effective filter. The heat exchange coils inside the unit could become clogged and require disassembly to clean. Filter non-compliance invalidates the product warranty.Quest 335 and Quest 506 installation and maintenance manuals

Two things there. The coils are the failure mode — once dust gets past a missing or wrong filter and lands on a wet coil it cements itself in place, and getting it off means taking the machine apart. And the warranty language is not a formality. A five-year warranty on a unit is worth considerably more than a decade of filters.

Short of that, the 506 manual describes what a loaded filter does day to day: it reduces dehumidifier capacity and efficiency, and it can cause the compressor to cycle off and on unnecessarily on the defrost control.⁴ Anden's guide describes the same physics from the airflow side — as media loads with dust, static pressure builds and air stops moving through it easily, and a unit with an ECM blower will ramp up power to push against it.⁷ The machine keeps working. It just costs more and removes less water while it does.

Which is the honest argument for a schedule over an inspection. A filter that is visibly filthy has been costing you capacity for weeks.

Changing it without getting it wrong

The job takes about two minutes and there are exactly four ways to get it wrong. All four are common enough that both manufacturers address them.

The first is direction. Pleated media is not symmetrical, and every frame carries a printed airflow arrow. Anden's own instruction is the simplest way to never get it wrong: install the new filter in the same direction the old one came out.⁶ Note which way the arrow pointed before you pull it, and match it.

The second is count. Most of these units take one filter. The Quest 506, 706, 746 and 876 take two, and replacing one of a pair leaves the airflow across the coil uneven while costing you most of the benefit. Change both at once.

The third is washing. This comes up constantly and the answer is the same for every filter in the tables above: the media is disposable. A pleated MERV filter traps particles inside the depth of the fibres, not on the surface, so rinsing it drives the load deeper and soaking it collapses the pleat structure that gives the filter its surface area. Vacuuming does less damage and also does very little good. There is no washable option in this range.

The fourth is substitution. A filter cut to fit, or a lower-rated one grabbed because it was on the shelf, is precisely what Quest's warranty language is written about. If the right part is not to hand and the room needs to run, run it with the old filter for another day rather than with none at all — a loaded filter costs capacity, and no filter costs coils.

That last step is the one nobody does and everybody should. A date on the frame turns a maintenance question into a glance.

Keeping filters on hand

The failure mode for filter maintenance is almost never a decision to skip it. It is a room that needs turning over on a Tuesday with no spare media in the building, and a filter change that quietly becomes a filter change next month.

Two things fix that, and neither is complicated. The first is holding one spare per machine. Every filter in the tables above is sold as a single, so the arithmetic is easy — count your units, keep that many on the shelf, and replace each spare as it goes into service. The Quest 506, 706, 746 and 876 count as two, since they take a pair.

The second is putting the restock on a schedule instead of a memory. Every filter in the tables above carries a Subscribe and save option on its product page alongside the one-time price, and the repeating option takes 5% off every delivery. The intervals offered are every two, three, four, six or eight weeks.

Set the quantity to the number of units you run and the eight-week interval becomes a rotation rather than a stockpile — each delivery replaces whatever came off the shelf and went into a machine since the last one. Nothing is sold as a fixed pack, so the count is yours to set and change. Eight weeks is shorter than either manufacturer's interval — twelve weeks from Anden, three to six months from Quest — so on a single dehumidifier a small buffer will build. That buffer is the spare you wanted on the shelf anyway.

Either way it removes a recurring decision. The filters show up, the room gets turned over, the coils stay clean, and the warranty language in the Quest manual stays theoretical.

If you are not certain which generation of unit you have, or your data plate does not match anything in the tables above, send us the model and serial from the plate and we will work it out with you. That is a faster conversation than a returned filter, and it is one we have most weeks. You can also reach the wider range through our dehumidifiers and humidity controllers pages if you are specifying a room rather than maintaining one.

FAQs

These are the six that come in most often, answered from the same manufacturer sources as the rest of the article.

How often should I replace a Quest or Anden dehumidifier filter?

Anden says every twelve weeks or at the end of a harvest.⁶ Quest's 506 manual says every three to six months, or in a growing environment at least once per grow cycle; the 335 manual says at least every six months.^{3, 4} Changing filters when you turn the room over satisfies both. Every part in this article is stocked under replacement filters.

Which filter fits a Quest 225?

That depends on which 225 you have, and the pint rating will not tell you. A Dual 225 takes the 16 × 20 × 2 MERV 11, part 4021475-01, or the MERV 13 equivalent, part 4039391. A Next Gen 225 takes the 18 × 18 × 2 MERV 13, part 4042787.⁵ Read the model number on the data plate — 4035400 is a Dual, 4046100 is a Next Gen. The same split applies to the 155 and the 205.

Why does my filter measure smaller than the size on the box?

Because pleated filters carry two sizes. The nominal size is the catalogue figure, rounded up to whole inches; the actual size is what a tape measure reads, usually about half an inch under in each face dimension. Quest publishes the nominal figure for most of its media.⁵ A filter listed as 16 × 20 × 2 and one listed as 19.5 × 15.5 × 1.75 are the same part — on this site that part is 4021475-01, listed under its measured size.

Does a Quest 506 take one filter or two?

Two, and so do the 706, 746 and 876. All four take part 4038233, which is sold as a single, so a full change is two of them.⁵ Replace both at the same time — running one new filter against one loaded one leaves the airflow across the coil uneven and gives up most of the benefit.

Is MERV 13 worth it over MERV 11?

In the one-to-three micron band, where most indoor fungal spores sit, the EPA's minimum for MERV 11 is 65% and for MERV 13 is 85%.¹ In a sealed room turned over every few months that gap is worth having. On the Quest Dual units both grades fit the same slot, so moving from the MERV 11 to the MERV 13 is a straight swap. Every current Anden dehumidifier ships with MERV 11 media and Anden publishes no MERV 13 option for them.⁸

Can I wash a dehumidifier filter and put it back in?

No. Every filter in the tables above is disposable pleated media, and neither brand lists a washable version. A pleated filter holds particles inside the depth of the fibres rather than on the surface, so rinsing drives the load further in and soaking collapses the pleats that give the filter its area. Vacuuming does less harm and also very little good.

References

Every dimension, part number, interval and efficiency figure in this article comes from one of the sources below. On their own equipment the manufacturer is the authority — what fits, what size it is, how many it takes and how often to change it all follow Quest and Anden. The EPA entries define what the MERV and HEPA ratings themselves mean, which is a separate question from what any one filter is.

1. United States Environmental Protection Agency, What is a MERV rating? — the 1-to-16 scale, the 0.3-to-10 micron range, and the banded minimum efficiencies for MERV 8, 11 and 13. epa.gov/indoor-air-quality-iaq/what-merv-rating
2. United States Environmental Protection Agency, What is a HEPA filter? — the 99.97% at 0.3 micron definition and the most-penetrating-particle-size explanation. epa.gov/indoor-air-quality-iaq/what-hepa-filter
3. Quest, Installation, Operation and Maintenance Instructions — Quest 335 — filter inspection and replacement interval, and the warranty language quoted above. questclimate.com — Quest 335 manual (PDF)
4. Quest, Installation, Operation and Maintenance Instructions — Quest 506 (TS-2041) — the three-to-six-month and per-grow-cycle guidance, and the capacity and defrost effects of a loaded filter. questclimate.com — Quest 506 manual (PDF)
5. Quest Climate, Accessories — published filter sizes, Quest part numbers and unit compatibility for every Quest filter in the first table. questclimate.com/accessories
6. Anden, Frequently Asked Questions — the twelve-week replacement interval and the four-step filter change procedure, including installing in the same direction. anden.com/faq
7. Anden, The Complete Guide to Dehumidifier Filters for Growers — the per-cycle recommendation and cross-contamination reasoning, the MERV 11 capture claim, and the static pressure and ECM blower explanation. anden.com — dehumidifier filter guide
8. Anden, Replacement Parts — published dimensions, MERV rating and model compatibility for every Anden filter in the second table. anden.com/products/replacement-parts

Sizes marked as measured come from the product listings on this site rather than from a manufacturer sheet, and the Quest 70 Pint pre-filter dimension is a store listing figure for the same reason — Quest does not publish that part on its accessory index. Both are identified as such wherever they appear.