Sizing
Whole house vs room humidifier
This is a capacity question before it is a convenience question. Above about six gallons a day, portables stop being an option and start being a collection of chores.
By Scooter M. · Published · Updated
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| # | Product | Best for | Gal/day | Price |
|---|---|---|---|---|
| 1 |  Aprilaire Model 700Top pickEighteen gallons a day against a stated 5,300 sq ft, cited to AHRI Guideline F. It is ducted, it needs installing, and it is the only sizing claim here with a standard behind it. | An actual whole house, sized against a standard | 18.0published · 5,328 sq ft | |
| 2 |  Levoit Superior 6000SSix gallons, evaporative, and a Dry Mode that dries the wicks between runs. The 3,000 sq ft claim needs five times the output its own run time implies. | Mist-free humidification with a drying cycle | 2.0implied · 592 sq ft | |
| 3 |  AIRCARE MA0800 Mini-ConsoleA 2.5-gallon evaporative console with three fan speeds, an adjustable humidistat and a MAF2 SuperWick. Its 2,600 sq ft claim is far beyond what its own tank and run time imply, so size it as a large room rather than a floor. | A plug-in console with its own humidistat | 1.7implied · 493 sq ft | |
| 4 |  Vornado Evap40Vornado publishes an output figure and a coverage figure, and the two agree. Four gallons a day covers about 1,180 sq ft at our derived rate against a 1,000 sq ft claim. | The only coverage claim here the arithmetic supports | 4.0published · 1,184 sq ft |
Most comparisons of whole-house and portable humidifiers are written as a lifestyle question: do you want convenience, or do you want flexibility? That framing hides the actual decision, which is arithmetic. Above a certain daily output there is no portable that can do the job, and below it there is rarely a reason to cut into your ductwork.
We earn a commission if you buy through the links on this page, at no extra cost to you. It does not change what we recommend or the order the picks appear in. Full disclosure. Prices checked October 16, 2026.
| # | Product | Best for | Gal/day | Price |
|---|---|---|---|---|
| 1 | Aprilaire Model 700Top pickEighteen gallons a day against a stated 5,300 sq ft, cited to AHRI Guideline F. It is ducted, it needs installing, and it is the only sizing claim here with a standard behind it. | An actual whole house, sized against a standard | 18.0published · 5,328 sq ft | |
| 2 | Levoit Superior 6000SSix gallons, evaporative, and a Dry Mode that dries the wicks between runs. The 3,000 sq ft claim needs five times the output its own run time implies. | Mist-free humidification with a drying cycle | 2.0implied · 592 sq ft | |
| 3 | AIRCARE MA0800 Mini-ConsoleA 2.5-gallon evaporative console with three fan speeds, an adjustable humidistat and a MAF2 SuperWick. Its 2,600 sq ft claim is far beyond what its own tank and run time imply, so size it as a large room rather than a floor. | A plug-in console with its own humidistat | 1.7implied · 493 sq ft | |
| 4 | Vornado Evap40Vornado publishes an output figure and a coverage figure, and the two agree. Four gallons a day covers about 1,180 sq ft at our derived rate against a 1,000 sq ft claim. | The only coverage claim here the arithmetic supports | 4.0published · 1,184 sq ft |
Start with the number
Work out what your space needs in gallons per day using the sizing chart, then read across:
| Requirement | Roughly | The honest answer |
|---|---|---|
| Under 2 gal/day | One or two rooms | A portable. A whole-house install is overkill. |
| 2 to 6 gal/day | An open floor, or several rooms | A large evaporative portable or a console. Still no need for ducting. |
| 6 to 12 gal/day | Most of a house | Genuinely borderline. Two or three consoles will do it, badly. A ducted unit will do it well. |
| Over 12 gal/day | A whole house, tightly built | Ducted. No portable in our set publishes an output that reaches this. |
What the ducted unit actually buys you
The Aprilaire 700 in our picks publishes 18 gallons a day against a stated 5,300 square feet, cited to AHRI Guideline F. That is more than four times the output of the largest portable here, and it arrives without a single refill.
The less obvious advantage is that it has no reservoir. It is plumbed to the water supply and drains to waste, so water never stands inside it. Every maintenance problem that dominates portable humidifier ownership - the pink film, the mold in the tank, the three-day cleaning cycle the EPA recommends - is a consequence of standing water, and a drained unit simply does not have it. Its consumable is a Water Panel changed once or twice a heating season, against a wick every 30 to 60 days.
What it costs you
- A ducted forced-air system. No ducts, no install. Boilers, baseboard electric and mini-splits are all disqualifying, and none of them is fixable.
- A water line and a drain within reach of the plenum.
- An installer, unless you are genuinely comfortable cutting an opening in a furnace plenum and making a saddle-valve connection.
- Owning the house. This is not a renter's purchase.
- Wasted water. The drain design that keeps it clean sends water down it.
The full break-even, including what several portables cost to run and refill across a season, is on whole house humidifier cost.
The case for portables that people undersell
A portable humidifies the room you are in. A whole-house unit raises the humidity of the air passing through your ductwork, which reaches rooms in proportion to how well your ducts are balanced - and in most houses they are not balanced well. If the problem you are solving is a dry bedroom, a bedroom unit solves it directly and a ducted unit solves it eventually, indirectly, and only when the furnace fan is running.
That last clause matters more than it sounds. A ducted humidifier only humidifies while air is moving. On a mild day when the furnace barely cycles, it barely runs. A portable does not care what the heating is doing.
The honest recommendation
If your requirement is under six gallons a day, buy a portable and put it where you actually are. If it is over twelve and you own a house with ducts, install a whole-house unit and stop thinking about it. Between six and twelve, the deciding question is not capacity but temperament: are you a person who will refill and clean two consoles every day for five months? If yes, portables are cheaper and more targeted. If no, you will end up with two dirty consoles and a dry house.
The picks, in full
Top pick · An actual whole house, sized against a standard
Aprilaire Model 700
Eighteen gallons a day against a stated 5,300 sq ft, cited to AHRI Guideline F. It is ducted, it needs installing, and it is the only sizing claim here with a standard behind it.
This is the reference point for the whole site. Aprilaire is the only maker in our set that publishes a capacity in gallons per day and a coverage in square feet together, and cites the residential sizing standard as the basis for pairing them. Three of its models do it consistently: 12 gal/day to 3,600 sq ft, 17 to 5,000, and 18 to 5,300. Those three pairs are where our 296 square feet per gallon per day comes from.
Everything else follows from the fact that it drains. There is no reservoir, so there is no standing water, so the pink film and the mold that dominate portable-humidifier ownership simply do not arise. The Water Panel goes once or twice a heating season instead of a wick every 30 to 60 days, which changes the recurring cost by an order of magnitude.
The honest counterweight is that this is not a purchase, it is a project. It mounts in ductwork, it needs a water line and a drain, it needs a humidistat and an outdoor sensor, and unless you are comfortable cutting into a plenum it needs a contractor. Our whole-house cost page works through the break-even against running several portables.
What works
- The only sizing claim in this set with a published standard behind it
- No reservoir, so no standing water and none of the maintenance that follows from it
- Water Panel changed once or twice a season instead of a wick every month or two
What does not
- Requires ducted forced-air heating, a water supply, a drain and, realistically, an installer
- Installed cost is a different order of magnitude from any portable here
- Wastes water: the drain design that keeps it clean also sends water to waste
Skip this ifyou rent, or you heat with anything other than a ducted forced-air system. Neither is a fixable objection.
The arithmetic
- Published output (continuous)
- 18.0 gal/day
- Covers, at 296 sq ft per gal/day
- 5,328 sq ft
- Maker’s coverage claim
- 5,300 sq ft
- Output that claim would need
- 17.9 gal/day
Output as the manufacturer publishes it. Coverage rate derived from Aprilaire’s own published capacity-and-coverage pairs.
Published specification
- Tank
- not publishedThere is no tank. It is plumbed to the water supply and drains to waste.
- Output/day
- 18 gal/daySource
- Coverage
- Up to 5,300 sq ftAprilaire states this for tightly constructed homes and cites AHRI Guideline FSource
- Power
- 24 VAC via the supplied transformerSource
- Filter
- Model 35 Water PanelAprilaire's maintenance page puts this on an annual schedule, plus an annual distribution-tray inspection. Its product page says once or twice per heating season; the two documents differ and we take the more specific one. Either way it is by far the longest interval of any unit here.Source
- Cleaning
- Built-in drain flushes mineral build-upWater does not stand inside the unit, which removes the standing-water problem entirelySource
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Pick 2 · Mist-free humidification with a drying cycle
Levoit Superior 6000S
Six gallons, evaporative, and a Dry Mode that dries the wicks between runs. The 3,000 sq ft claim needs five times the output its own run time implies.
Six gallons over 72 hours is two gallons a day, which covers about 590 square feet. The box says 3,000. To actually hold humidity across 3,000 square feet this unit would need to move a little over ten gallons a day, and at that rate its six-gallon reservoir would run dry in about fourteen hours. Both numbers describe the machine; only one describes it at a time, and the maker publishes no figure that reconciles them.
Dry Mode is the genuinely good idea here and it deserves credit. A wet wick sitting in a warm room is the substrate for everything the EPA warns about, and a fan cycle that dries the wicks between runs attacks that problem directly rather than adding an antimicrobial coating and hoping. It also extends wick life, which is the recurring cost.
Thirty watts to move two gallons a day is efficient, and mist-free operation means the minerals stay in the wicks rather than settling on your furniture. If you can live with a coverage claim you should mentally divide by five, this is a well-made machine.
What works
- Dry Mode addresses the real failure mode of evaporative units instead of masking it
- Mist-free, so no white dust whatever your water is like
- 30 W for six gallons of capacity, with noise published at both ends of the range
What does not
- The 3,000 sq ft claim is about five times what the published tank and run time imply
- Four wicks to replace, on an interval Levoit does not publish
- 45 dB at the top of the fan range is audible in a quiet bedroom
Skip this ifyou bought it for the 3,000 sq ft number. Size it at around 600 square feet on the setting whose run time Levoit actually publishes.
The arithmetic
- Implied output (low fan speed)
- 2.0 gal/day
- Covers, at 296 sq ft per gal/day
- 592 sq ft
- Maker’s coverage claim
- 3,000 sq ft
- Output that claim would need
- 10.1 gal/day
Output derived as tank capacity divided by published run time, times 24. Coverage rate derived from Aprilaire’s own published capacity-and-coverage pairs.
Published specification
- Tank
- 6 gal / 22.7 LSource
- Output/day
- not published
- Coverage
- 3,000 sq ft / 279 m23,000 sq ft needs about 10.1 gal/day at our derived rate. Its published tank and run time imply 2.0.Source
- Run time
- Up to 72 hOn the low fan speedSource
- Power
- 30 WSource
- Noise
- 28-45 dBSource
- Filter
- Four wick filters, pre-installedReplacements are sold by Levoit as a four-pack. No replacement interval is published.Source
- Cleaning
- Dry ModeLevoit's own wording: low and high fan speeds dry out the elevated wick filters, extending filter lifeSource
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Pick 3 · A plug-in console with its own humidistat
AIRCARE MA0800 Mini-Console
A 2.5-gallon evaporative console with three fan speeds, an adjustable humidistat and a MAF2 SuperWick. Its 2,600 sq ft claim is far beyond what its own tank and run time imply, so size it as a large room rather than a floor.
Two published figures that describe opposite ends of the machine, and none of the numbers that would join them up. A 2.5-gallon tank lasting 36 hours is about 1.67 gallons a day, or roughly 493 square feet at our derived rate. Covering the claimed 2,600 square feet would take about 8.8 gallons a day, at which rate the same tank empties in under seven hours.
Both can be true at once: 36 hours is AIRCARE's maximum run time, which will be the lowest of the three fan speeds, and 2,600 square feet will be the highest. It can certainly move more than 1.67 gallons a day on a higher speed. AIRCARE does not say how much more, so its own published data supports sizing it as a large room, not a whole floor.
What it has that most units in our set do not is an adjustable humidistat with digital controls, stated on AIRCARE's own page. On an evaporative machine, which already slows down as the air approaches saturation, that is a second brake against overshooting - and the MAF2 SuperWick keeps your tap water's minerals out of the air.
What works
- Adjustable humidistat and digital controls, per AIRCARE's own specification
- Evaporative SuperWick captures minerals, so no white dust
- Three fan speeds to trade output against noise
What does not
- No published output figure anywhere on the manufacturer page
- The 2,600 sq ft claim and the 36-hour run time cannot both describe the same setting
- No published noise figure, wattage or wick replacement interval
Skip this ifyou want to humidify a whole floor on the strength of the box. Its own tank and run time support a large room, not 2,600 square feet.
The arithmetic
- Implied output (maximum published run time)
- 1.7 gal/day
- Covers, at 296 sq ft per gal/day
- 493 sq ft
- Maker’s coverage claim
- 2,600 sq ft
- Output that claim would need
- 8.8 gal/day
Output derived as tank capacity divided by published run time, times 24. Coverage rate derived from Aprilaire’s own published capacity-and-coverage pairs.
Published specification
- Tank
- 2.5 galSource
- Output/day
- not publishedAIRCARE's page gives a tank capacity and a maximum run time, but no daily output.
- Coverage
- Up to 2,600 sq ft2,600 sq ft needs about 8.8 gal/day at our derived rate. AIRCARE publishes no output figure, so the claim cannot be checked against its own data.Source
- Run time
- Up to 36 hAIRCARE's maximum run time, which will describe the lowest of its three fan speedsSource
- Power
- not published
- Filter
- MAF2 SuperWickAIRCARE publishes no replacement intervalSource
- Cleaning
- Evaporative wick holds minerals back from the roomAdjustable humidistat and digital controls, per AIRCARESource
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Pick 4 · The only coverage claim here the arithmetic supports
Vornado Evap40
Vornado publishes an output figure and a coverage figure, and the two agree. Four gallons a day covers about 1,180 sq ft at our derived rate against a 1,000 sq ft claim.
Run the check that fails everywhere else on this page and it passes here. Four gallons a day at 296 square feet per gallon per day is about 1,180 square feet of coverage, against a claim of 1,000. Vornado left itself margin instead of taking it.
It passes because it is evaporative. A wick and a fan can only put as much water into the air as the air will accept, which is why an evaporative unit self-limits near 50% relative humidity and why it cannot produce white dust: the minerals stay in the wick. The EPA's guidance to use low-mineral water exists mainly because ultrasonic and impeller units disperse what is dissolved in the tank, and this design does not.
The cost of that is the wick. Two of them, on a schedule Vornado does not publish, which is the recurring bill an ultrasonic unit does not have. Whether that trade is worth it is arithmetic, and it is worked through in full on our filter-cost page.
What works
- Publishes an output figure, and the coverage claim survives being checked against it
- Evaporative, so it cannot produce white dust and self-limits near a safe humidity
- Five-year warranty, the longest published here
What does not
- Two wicks to replace on an interval Vornado does not publish
- A fan moving air across a wet wick is audible, and no dB figure is published
- No rated wattage published
Skip this ifyou want silence. Every evaporative unit is a fan, and Vornado publishes no noise figure for this one.
The arithmetic
- Published output (continuous on high)
- 4.0 gal/day
- Covers, at 296 sq ft per gal/day
- 1,184 sq ft
- Maker’s coverage claim
- 1,000 sq ft
- Output that claim would need
- 3.4 gal/day
Output as the manufacturer publishes it. Coverage rate derived from Aprilaire’s own published capacity-and-coverage pairs.
Published specification
- Tank
- 4 galSource
- Output/day
- Up to 4 galVornado's wording: up to a 4 gallon water output when operated continuously on highSource
- Coverage
- Up to 1,000 sq ftSupported by its own published output. This is the only unit in the set where that is true.Source
- Run time
- not publishedVornado publishes output instead, which is more useful
- Power
- not published
- Filter
- Two humidifying wicksTwo are supplied, one front and one rear. No replacement interval is published.Source
- Cleaning
- Vornado states easy to clean and operateSource
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Questions people actually ask
Are whole house humidifiers worth it?
If your house needs more than about six gallons of water a day and you have ducted forced-air heating, yes: no portable in our set publishes an output that reaches that, and a ducted unit has no reservoir, so it avoids the standing-water maintenance that dominates portable ownership. Below that figure it is usually a lot of installation for a job a portable already does.
Can a portable humidifier do a whole house?
Only a small one. The largest published portable output in our set is 4 gallons a day, which covers about 1,180 square feet at our derived rate, and that assumes the air can actually circulate. Closed doors change the answer more than square footage does.
Do whole house humidifiers need cleaning?
Far less. A ducted unit like the Aprilaire 700 has no tank, is plumbed to the supply and drains to waste, so water does not stand inside it. Its consumable is a Water Panel that Aprilaire's maintenance page puts on an annual schedule, against a wick every 30 to 60 days on a portable. Less is not none - see mold in a furnace humidifier.
Will a whole house humidifier work with a boiler or baseboard heating?
No. A ducted whole-house humidifier needs forced-air ductwork to put moisture into. With hot-water baseboard, radiators or mini-splits there is no air stream to humidify - and a whole-house steam unit does not rescue you either, because it injects its vapor into the duct as well. Portables are the option: humidifiers with no ductwork covers what they can actually hold.
Sources
Every figure on this page came from one of the documents below, read on the date shown. We do not cite other review sites, forum posts or video reviews as sources of fact.
- Aprilaire Model 700 - manufacturer spec page (retrieved September 1, 2026)
- AIRCARE MA0800 Mini-Console - manufacturer spec page (retrieved September 17, 2026)
- Levoit Superior 6000S - manufacturer spec page (retrieved September 1, 2026)
- Vornado Evap40 - manufacturer spec page (retrieved September 1, 2026)
- AHRI Guideline F - Selection, Installation and Servicing of Residential Humidifiers (the residential sizing standard; ahrinet.org returned HTTP 403 to this build, so we cite it as the governing document without paraphrasing text we did not read)
- US Environmental Protection Agency - Use and Care of Home Humidifiers (relative humidity ceiling, three-day cleaning interval, low-mineral water, microorganism warning)
Read next
Whole house
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The ownership case for a ducted humidifier against multiple portables, with the consumable arithmetic and an honest statement of what we cannot cost.
Top pick: Aprilaire Model 700 · 18.0 gal/day
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Whole house
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How ducted whole-house humidifiers work, the drainage advantage that changes their maintenance entirely, and the requirements that rule most people out.
Top pick: Aprilaire Model 700 · 18.0 gal/day
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Humidifier sizing chart by square footage
The sizing chart in gallons per day, by floor area and ceiling height, with a companion table of what each figure means in practice.
Best for apartments
Best humidifiers for an apartment
Apartment picks chosen around the constraints a house does not have - condensation on someone else's windows, a neighbor through the wall, and nowhere to put a console unit.
Top pick: Levoit Classic 300S · 0.63 gal/day
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How many
How many humidifiers do you need?
Working out the count rather than the size: why output only adds up within one open space, what each extra machine costs you in daily maintenance, and when the honest answer is one ducted unit.
Top pick: Vornado Evap40 · 4.0 gal/day
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Best without ducts
Best humidifiers when you have no ductwork
The honest options for a house with no forced-air ductwork: what the largest portables actually deliver, why no machine is really a whole-house unit, and how to cover a house with two or three of them.
Top pick: Vornado Evap40 · 4.0 gal/day
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Found a number that is wrong? Tell us and we will fix it and say so. How we pick shows every formula used on this page.