Longest between refills, honestly measured

Honeywell's answer to the two complaints levelled at the HCM-350: no digital humidistat, and a tank you have to carry upside down to the sink. The HEV620 is a tower with a top-fill opening, a digital humidistat that will actually hold a target, and a timer. Its 300 sq ft claim against 2 gallons a day of output is one of the most conservative ratios in the catalog - the output supports closer to 490 - which is worth knowing if you have been talked out of it by a spec-sheet comparison against an ultrasonic promising 750. Honeywell now sells it in black (HEV620B); the white HEV620W pictured is discontinued.

The LW25's larger sibling: a 3-gallon basin, the same disc stack and eight watts at full speed, sold for 645 sq ft. Like the LW25 it comes with no output rate - not on Venta's product page and not in the LW15/LW25/LW45 manual - so the 645 sq ft has nothing behind it a buyer can check; the three gallons a day some retailers quote belongs to the older Venta Original LW45. Venta has since moved on: its US store shows both colours out of stock and names the AH550/AH555 Original Connect as the newer model. No wick, a two-year limited warranty, and a basin you will have your hands in every couple of weeks.

Ten litres is a floor-standing amount of water, and that is the whole proposition here - Levoit's answer to people who were tired of filling a 6L tank every other day. The 100-hour runtime figure is real at the lowest setting and is the longest in the catalog. Levoit's manual also gives a maximum output of 350 mL an hour, which is 2.2 gallons a day and supports about 550 square feet, close to the 600 on the box; at that rate the ten litres last a little over a day. It is still an ultrasonic, so the white-dust and tank-hygiene arithmetic is unchanged, and a bigger reservoir means more standing water to keep clean rather than less.

A litre more tank than the HM311S, from the same playbook: humidity sensor, app, top fill and a 28 dB low setting. Dreo rates it for 300 sq ft, the same room as the smaller unit. That room calls for about 1.2 gallons a day, which would take the 5-litre tank down in roughly 26 hours against the 42 advertised - a modest stretch rather than a wild one. Neither Dreo ships a demineralisation cartridge in the box, and the 512S takes a different one from the 311S, sold as a $25.99 three-pack, so on hard water budget for it from the start. Against the HM311S the extra $20 buys a litre of water and not much else: both have an aroma pad tray, a sensor and the same app.

Eight watts at full speed, no wick and no filter - Venta's disc-stack airwasher costs a great deal up front and almost nothing to run, which is the whole argument for it. Its manual is also the only one in this catalog that states the assumption behind its room-size figure: "listed square feet are based on 8-foot ceilings". That single sentence is more transparency than the rest of the category manages combined. What Venta will not tell you is how much water it actually moves - no output rate appears in the manual or on the product page - so the 485 sq ft figure has nothing behind it that a buyer can check.

A boiler with a tank on it, and the oldest idea in the category. Steam humidifiers have no ultrasonic disc to scale, no wick to replace and no fan to hear - the water boils, minerals stay in the pot, and what leaves the machine is distilled by definition. That is why the V745A shows up in so many nursery and sick-room recommendations despite being unchanged for well over a decade. It is also 260 watts of a hot electrode boiling water in a room with a child in it, twelve hours to a tank, and an appliance you descale rather than rinse. The 250 sq ft on the box is the most conservative figure Vicks publishes; two gallons a day would hold nearly twice that.

Four gallons of water, four gallons a day of output, a full day between fills at the top speed, and a 1,000 sq ft claim that the load calculation puts at 985. Vornado states the runtime honestly too - four gallons in 24 hours run continuously on high - which is the sentence almost nobody else in this category is willing to write. It is the smallest true console here and the one to buy if the AIRCARE units are more furniture than a room can take. Made in the USA, five-year guarantee, and still just a fan blowing through two wet wicks.

Vornado prints room sizes that the physics actually backs up. One gallon a day supports about 246 square feet by the standard winter calculation; Vornado prints 260 on the box. That is not a rounding coincidence - the same relationship holds across their whole line, which means somebody there is doing the load calculation instead of the marketing. The EV100 itself is a plain, small, well-built evaporative: one gallon, one wick, automatic humidity control, and a five-year guarantee that is unusually long for the money. It will not humidify an open-plan floor, and Vornado does not claim it will.

Fifty dollars buys the parts that usually cost more: a 4-litre top-fill tank, a real humidity sensor, app control and a 28 dB low setting. The demineralisation cartridge is the part to read carefully. The HM311S takes one, but the $49.99 listing does not include it - Dreo sells it as an $18.99 three-pack or in a $54.99 bundle - and without it the unit atomises whatever minerals are in the tap water, like any other ultrasonic. On the 300 sq ft Dreo prints, the arithmetic is tight rather than wrong: that room wants about 1.2 gallons a day, which would drain the tank in about 21 hours rather than the 32 advertised.

Eight litres, warm and cool mist and a published 550 mL/hr - on paper the most complete portable in Dreo's line, though the demineralisation cartridge that would stop white dust is a separate purchase: $25.99 for three, or a $145.98 listing that bundles one against $119.99 without. The extra two litres over the HM713S buy about two and a half more hours at full output rather than the twenty the runtime figures suggest, because the 80-hour number is again the lowest setting. Where it genuinely earns the money is the middle: run it on auto in a 400 sq ft bedroom and it will go two or three nights between fills without a chilly mist.

A tower with a 1.47-gallon tank, a demineralisation cartridge in the box, and a 426 sq ft claim - an oddly specific number that at least suggests somebody calculated rather than rounded up to 500. HoMedics now lists it as the Decor Series Large Humidifier, and its box gives the CMTF91 a 17-18 dBA noise figure, which with the cartridge makes it one of the quiet, dust-free units here. Seventy hours on the lowest setting is among the longest here, which as usual means the lowest setting moves very little water: about half a gallon a day. Where it earns its place is the combination of a demineralisation cartridge and a real humidistat at $100, which most rivals at this price do not offer.

Honeywell's filter-free line exists because plenty of people would rather buy no consumables than buy the right ones. There is no wick and nothing to replace, which keeps ownership about as cheap as it gets here - and it is an ultrasonic with no demineralisation media, so on hard water the minerals that a wick would have caught end up on the furniture instead. A gallon tank and 24 hours works out to about a gallon a day, near enough to what its 300 sq ft claim needs, making this one of the more honest small ultrasonics on that particular number.

Dreo publishes 500 mL/hr for this one, which is 3.17 gallons a day and puts it in the same real-output bracket as Levoit's LV600S at a slightly lower price. Like the Levoit, it makes white dust on hard tap water unless you add a demineralisation cartridge, which Dreo sells separately. The 500 sq ft claim is well inside what 3.17 gal/day actually supports - around 780 by the psychrometrics - making this one of the few portable ultrasonics whose room-size number is conservative rather than aspirational. The catch is the same as every hybrid: at the output that justifies the claim, the 6-litre tank is empty in about twelve hours.

Sixty hours of runtime and 505 square feet cannot both be true at once, and the Classic 300S is the clearest illustration of that in the whole catalog. Drain a 6-litre tank over the advertised 60 hours and the unit is putting out about 0.63 gallons a day, which is bedroom-sized. Hold 505 square feet at 40% and it needs roughly 2 gallons a day, which empties that same tank in under 19 hours. Both numbers come off Levoit's own spec sheet; only the setting changes. What you actually get for $80 is a competent, genuinely quiet ultrasonic for one room, with top filling, a real humidity sensor, an auto mode that targets 40-50%, and app control that owners either use constantly or never touch again. It is an ultrasonic with no demineralisation media, so hard tap water becomes white dust on the nightstand, and the tank wants weekly cleaning or it turns pink.

The cheap one, and honest about being cheap. No humidity sensor, no app, no auto mode - a dial, a 2.5-litre tank, a filter sponge and a top-fill opening. For a small bedroom or a desk that is often exactly enough, and the absence of a sensor means there is nothing to drift out of calibration. It is also, unexpectedly, one of the more truthful boxes here: Levoit publishes 190 mL/h at the top of the dial, which is about 1.2 gallons a day and enough for nearly 300 square feet, more than the 219 its own manual claims. The catch is that Levoit's two runtime numbers describe opposite ends of that dial - 25 hours at the 100 mL/h minimum, 11 at the top. What it cannot do is hold a target: it runs at whatever you set until the tank is empty, which in a small closed room means over-humidifying and a damp window.

Take the HCM-350's mechanism and move the fill to the top: water goes in through a funnel on the lid, so nothing has to be carried to the sink, and that is most of what "Easy to Care" means. The trade is capacity: a 1-gallon tank against the 350's 1.1, no UV, and no humidistat here either. Neither Honeywell's manual nor its store page says any part is dishwasher safe, unlike the HCM-350, whose tank and tray are. At the 36 hours Honeywell claims it is moving two thirds of a gallon a day, which is a bedroom's worth; the 360 sq ft it is sold for would take closer to 1.5 gallons a day and drain the tank in about 16 hours.

A thousand dollars, and the humidifier is the third thing it does. The PH04 is primarily an air purifier with a formaldehyde-destroying catalytic filter and a fan, into which Dyson has fitted an evaporative humidifier with a UV-C water treatment stage and a deep-clean cycle. Judged as a humidifier it is modest: a 1.1-gallon tank, a 400 sq ft claim, and no published output rate at all, which for a company that publishes airflow in litres per second is a conspicuous omission. It belongs in this catalog because people cross-shop it, not because it is the best way to spend $1,000 on humidity.

Adding a heater to an ultrasonic buys two things: mist that does not feel cold on the skin, and a water path that runs hot enough to discourage what grows in a tank. It costs a 280W draw against the Classic 300S's 26, which is the difference between a rounding error on the power bill and a space heater you left on. The 450S is the counter-top size in Levoit's line - a 4.5-litre tank on a footprint small enough for a nightstand, quieter on its lowest setting than almost anything else here at 26 dB. It claims 430 square feet; the arithmetic says holding that room takes about 1.75 gallons a day, so the tank would last around 16 hours rather than the advertised 45.

One 1.38-gallon top-fill tank, warm and cool mist, a demineralisation cartridge in the box, a humidistat and an eighty-five-hour low-setting claim - one of the longest numbers in this catalog, and the one that best illustrates why the number is nearly meaningless. Eighty-five hours from 1.38 gallons is 0.39 gallons a day, about a fifth of what the 521 sq ft printed alongside it would require. HoMedics also prints 21-23 dBA for it, which with the cartridge puts it among the quiet, dust-free units here, and adds an eight-hour auto-off timer.

Two tanks instead of one, two wicks instead of one, and 2.4 gallons a day against a 580 sq ft claim - within about two percent of the load calculation, one of several Vornado figures that land that close. Refilling means carrying two 0.75-gallon tanks rather than one heavy one, which sounds like a downgrade and is not: most people find two light trips easier than one awkward one, and you can run it on a single tank overnight. Fifteen hours at full output is the honest tank life, and Vornado does not pretend otherwise.

Vicks sells more humidifiers through drugstore shelves than most of this catalog sells anywhere, and the VUL545 is the one people pick up at nine in the evening when a child has croup. It works: a gallon of water, visible cool mist, a scent pad slot for menthol, and no filter to have forgotten to buy. What it will not do is hold 400 square feet - that room wants about 1.6 gallons a day, about two and a half times what the advertised 36-hour run delivers - and on hard water it powders dark surfaces within a few days.

Where the VUL545 atomises, this one evaporates - a wick, a fan and a UV lamp in the reservoir. For anyone who bought a Vicks ultrasonic and then found white powder on the dresser, the V3900 is the same brand's answer, and it is the cheaper half of the answer compared with Honeywell's HCM-350. A gallon a day against a 400 sq ft claim overstates by about 60%, which is mild by the standards of this category. The wick is the ongoing cost, at roughly $14 every month or two, and the UV lamp treats the water in the tank rather than the air in the room.

The EVDC300's larger sibling: same DC motor and single-watt idle, two tanks instead of one, and enough output to matter in a real living room. At 3.5 gallons a day it is the most capable tabletop Vornado makes, and its 840 sq ft figure again sits within a few percent of the load calculation. Fourteen hours at full output, so still a daily job in a dry house - but two tanks make that a lighter job than one. The question it poses against the Evap40 console is whether you would rather carry water twice a day and keep the floor space, or once a day and give up a corner.

Four gallons a day from a tabletop unit, which puts the U700 level with Vornado's Evap40 console on output while taking up a fraction of the floor. Its 1,000 sq ft figure lands within two percent of the load calculation - Boneco and Vornado both print numbers the physics backs up. Its nine-litre tank still lasts only fourteen hours at full tilt, which is the recurring lesson of this category: capability and refill interval trade against each other and no amount of marketing changes it. The self-cleaning mode is genuinely unusual at any price.

An air washer works by turning textured evaporator mats through a water bath: air passes over the wet surfaces, picks up moisture, and drops some dust on the way. The appeal is that the mats are washed rather than bought by the season - Boneco says they go in the dishwasher or the washing machine - though it does sell replacement mats. Boneco's technical data gives 350 grams an hour, which is 2.22 gallons a day and supports about 547 sq ft, so the 540 on the listing is one of the few coverage claims in this catalog that its own maker's output figure actually backs. The rest of the arithmetic is as plain: a 4.5-litre bath, one silver stick a year, no filters, and about thirteen hours between fills if you are running it at the room it claims.

The long-running default in this category, and the arithmetic explains why. Honeywell's manual gives 2 gallons a day of output against the 500 sq ft it is sold for - a room that needs almost exactly that - making this one of the few portables in the catalog whose coverage number the physics supports outright. It was sold from 2011 largely unchanged until Honeywell discontinued it; the tank and tray go in the dishwasher, and it evaporates rather than atomises, so there is no white dust. The costs are a wick habit, a fan you can hear, and no humidistat at all: three speeds, and you are the humidistat.

Three washable parts, all stainless steel, all dishwasher safe - that is the entire product thesis and it is aimed squarely at the reason most humidifiers end up in a cupboard. Plastic tanks grow a pink film in the seams and scratch when you scrub them; a steel tank can be boiled, bleached or run through a dishwasher indefinitely. Carepod charges $350 for that, which is four times a Levoit with more capacity. It is still an ultrasonic with no demineralisation media, so hard water still means white dust, and the 500 sq ft Carepod prints is more than its own tank and runtime support: 4 litres over 30 hours is under nine-tenths of a gallon a day, enough for about 210 square feet.

One of the few units in the catalog where the maker publishes an actual output rate rather than leaving you to infer it: 550 mL/hr on warm, 300 on cool. That makes the LV600S checkable in a way most of its shelf-mates are not, and the check is unflattering in a useful way. At 550 mL/hr it moves 3.49 gallons a day, which is a genuinely capable figure - enough for around 860 square feet by the psychrometrics - but it empties the 6L tank in about eleven hours. The 50-hour runtime on the box is the cool setting at its lowest. Both numbers are honest; they just describe different machines. Owners who understand that and run it on auto in a bedroom are happy; owners who expected 50 hours of whole-floor humidification are the ones writing the angry reviews.

Swiss, expensive, and unusually straight about what it does: 3.17 gallons a day published, against a 650 sq ft claim that the load calculation puts at 780. A maker printing a number 17% below what its own output supports is doing something almost nobody else in this catalog does. It pairs a demineralisation cartridge with an Ionic Silver Stick for the water, so the two failure modes of a cheap ultrasonic - dust on the furniture, life in the tank - both have a specific countermeasure. The tank is only 5 litres, which at full output is about ten hours.

This is what happens when Levoit stops building ultrasonics. A 1,500 mL/hr published output works out to 9.5 gallons a day, which is console territory, and because it evaporates water through wicks rather than atomising it there is no white dust and no mineral film on the furniture. The 3,000 sq ft claim is one of the more defensible in the catalog: the physics supports around 2,300, so it overstates by about a third rather than the three- and four-fold gaps common among the ultrasonics. The cost is a wick habit - four of them, around $40 a set - and a unit you fill through a hose and funnel rather than lifting a tank. Owners who moved from an ultrasonic mostly describe the absence of dust as the thing they noticed first.

The teardrop shape has been on nursery shelves for over a decade and is probably the most recognisable humidifier in America. A gallon of water, twenty-four hours and no filter required, though Crane sells an optional demineralisation filter (HS-1932) that screws into the tank for hard water. Crane is inconsistent about what it covers: 500 sq ft on its own product page and on retail listings, 250 in its manual. The arithmetic supports the smaller figure: a gallon over 24 hours is about 246 square feet.

Crane's fix for the original Drop's two real problems - the bottom-fill tank and the neck you could not get a hand into - plus a sound machine and a colour-changing nightlight aimed squarely at nurseries. The top opening is wide enough to reach inside and scrub, which is the single most useful change and the reason to pay $5 more. Three sleep sounds, an aroma tray for vapour pads, and the same one-gallon, twenty-four-hour, no-filter arrangement underneath.

Pure Enrichment is unusually straight about runtime: it publishes a range, ten to twenty-four hours depending on the setting, rather than quoting only the flattering end. That one editorial choice tells you more about the machine than any spec - at the high setting a gallon lasts ten hours, which is what a gallon does. It is otherwise an unremarkable and perfectly competent $60 ultrasonic: no filter required, a mist dial, an optional nightlight, auto shut-off. The 500 sq ft claim holds only at the high setting, ten hours to a tank.

Sold on being easy to clean - a wide 3.5-litre tank you can get a whole hand into, which is a bigger deal than it sounds given that the narrow-necked tank is why most cheap humidifiers end up growing something. Pure Enrichment publishes its output as well as its runtime: up to 300 mL an hour, which is 1.9 gallons a day, twelve hours to a tank on high and fifty on low. That supports about 470 square feet, almost exactly the 475 it prints in its copy, though the spec table on the same page says 270. What you give up for the wide mouth is a sensor: there is no humidistat, so it runs at the level you set until it is empty, and in a small closed room that is how windows end up wet.

A DC motor is the only interesting thing here and it is interesting enough to justify the model. On its Energy Smart setting the EVDC300 draws as little as a single watt, against the fourteen to forty-five watts Vornado's AC evaporatives pull, and it runs the whole winter for the price of a few coffees. Output is 2.3 gallons a day - within one percent of what its 560 sq ft claim actually needs - from a one-gallon tank, which is the catch: ten hours between fills if you run it hard. It is the fill interval, not the capability, that decides whether this or the two-tank EV200 is the right one.

A Swiss design-led cube that has been on sale, essentially unchanged, for over a decade - which in a category full of two-year model cycles is its own recommendation. Output is a published 1.9 gallons a day against a 540 sq ft claim; the load calculation supports about 470, so it overstates by fifteen percent, which is modest for this category. The tank is only 0.9 gallons, which at full output is about eleven hours. Eighteen watts at most, a real hygrostat, and a cube small enough to sit on a bookshelf.

The One Plus with a heater, which buys warm mist and - more interestingly - a one-touch cycle that boils the tank to sterilise it. Between a steel water path and a heat-sanitise button, this is as close as the category gets to solving the hygiene problem outright, and it is priced accordingly at $450. Carepod buries its output rate in a feature graphic rather than a spec table, which is a shame because it is one of the better ones here: 440 mL/h on warm is 2.79 gallons a day, and that makes the 700 sq ft on the listing very nearly honest. The catch is the tank. At that output 4.2 litres is gone in about ten hours, against the 32 advertised at the lowest setting.

The MA1201's output in the wood-finish cabinet AIRCARE calls the Alliance, with half again as much water, which is the version of this machine that makes sense for a house you actually live in. Same 12 gallons a day, but 5.4 gallons of reservoir stretches the fill interval from seven hours to eleven at full tilt, and four speeds with an auto humidistat mean it rarely runs at full tilt. It is heavy and it is furniture, but it does a job that otherwise requires a plumber and a hole in your ductwork. Not to be confused with AIRCARE's Credenza, a different 5.6-gallon, nine-speed model.

AIRCARE's concession to the fact that a console humidifier is a large brown box in a living room. The EP9800 is the same machinery in a pedestal cabinet with a wood finish, meant to look like furniture rather than an appliance - and it half succeeds, which is more than the MA1201 attempts. Nine fan speeds is genuinely useful granularity when you are trying to find the setting that is quiet enough to live with. Output is 7.4 gallons a day against a 2,400 sq ft claim; the calculation supports about 1,820, so it overstates by a third.

Canopy sells cleanability, and on that promise it delivers better than anything else here: tank, tray, cap and grille all go in the dishwasher, the filter is on a 45-day clock the machine reminds you about, and because it evaporates rather than atomises there is no mist to land on anything. What $159 does not buy is capacity or control. There is no humidistat, and 2.5 litres across the advertised 36 hours is under half a gallon a day - a figure that supports something closer to 110 square feet than the 500 on the listing. As a nightstand appliance for one person's immediate airspace it is excellent. As the 500 sq ft room humidifier the marketing describes, it is not close.

Mechanically the Bedside 2.0 - same tank, filter, red light, nightlight and three soundscapes - sold with Canopy's baby-safe Little Dreams aroma kit and in nursery colours. The argument for it in a child's room is specific and good: no visible mist means nothing lands in a cot, no ultrasonic means no white dust in a room where a baby is breathing, and the dishwasher-safe parts mean the cleaning actually gets done at the interval it needs. The same capacity ceiling applies - this is one cot's worth of air, not a 500 sq ft nursery - and there is no humidistat to stop it when the room is where you want it.

Twelve gallons a day puts it level with the H12-400HB at the top of the portables in this catalog, and it is the reason people with genuinely dry old houses end up here rather than buying four bedroom units. The load calculation puts 12 gal/day at around 2,950 square feet against AIRCARE's 3,600 - an overstatement of about a fifth, which in this category counts as restraint. The number that surprises people is the tank: 3.6 gallons feeding 12 gallons a day is roughly seven hours at full output. The 36-hour figure is the lowest of four speeds. Owners of dry houses fill this thing twice a day in January and consider it worth it.

Sold through West Elm and QVC rather than a hardware aisle, which tells you what it is optimised for - a slim tower in a walnut-and-white finish that looks like a speaker. Despite the "Hybrid" in its name it is a cool-mist ultrasonic with no heater - Objecto's own spec reads "Ultrasonic, Cool Mist" - and while the four mist levels are real, a 2.4-litre tank is the smallest of anything here claiming 650 square feet, and twenty-two hours of runtime from it works out to under 0.7 gallons a day. Holding the room it claims would empty the tank in under six hours. Buy it because you want that object on that table; the arithmetic is not the reason.