Types
Steam vs evaporative whole house
The two whole-house technologies split on one question: does your humidifier need to work when the furnace is not running? Everything else follows from that.
By Scooter M. · Published · Updated
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 13, 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 | Check price#ad |
| 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 |
Both mount in ductwork, both are plumbed to the water supply, and both humidify a whole house. They differ in where the energy to evaporate the water comes from, and that single difference produces every other difference between them.
An evaporative unit uses the furnace's own warm air. Air is pulled across a wet water panel, and evaporation does the rest. A steam unit boils the water electrically and injects the vapor into the duct.
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 13, 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 | Check price#ad |
| 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 |
The furnace dependency, which is the real decision
It matters more than the specification sheets suggest. On a mild day when the furnace barely fires, an evaporative unit barely runs - exactly when a shoulder-season house can still be dry. In a well-insulated modern home that calls for heat infrequently, the evaporative unit's duty cycle is tied to somebody else's schedule.
Heat pumps sharpen this further. They deliver air at a lower supply temperature than a gas furnace, and evaporation rate depends on how much moisture that air can pick up. Cooler supply air evaporates less water from the same panel.
Capacity
| Technology | Model | Capacity published | Coverage stated |
|---|---|---|---|
| Evaporative, bypass | Model 500 | 12 gal/day | 3,600 sq ft |
| Evaporative, water-saving | Model 400 | 17 gal/day | 5,000 sq ft |
| Evaporative, fan-powered | Model 700 | 18 gal/day | 5,300 sq ft |
| Steam | Model 800 | up to 34.6 gal/day | not stated as a square-footage figure |
Roughly double at the top end. Aprilaire states the steam figure as up to 34.6 gallons per day in a tightly constructed home, and notes that its coverage figures reference AHRI Guideline F for average construction homes. At our derived rate of 296 sq ft per gallon per day, 34.6 gal/day is the top of the residential range by a comfortable margin - see the whole house sizing chart.
Note what we are not doing there: Aprilaire publishes a square-footage figure for its evaporative models and we could not find one stated the same way for the steam model, so we have left that cell as not stated rather than computing one and presenting it as theirs.
Running cost, where evaporative wins decisively
Boiling water is the only genuinely energy-hungry thing any humidifier does. An evaporative whole-house unit runs a 24 VAC transformer and, on a fan-powered model, a small fan - its draw is negligible against household heating. A steam unit is an electric boiler.
Aprilaire describes the steam model's output as varying with voltage and current draw, which is the honest way to put it: capacity and electricity consumption are the same dial. We are not going to publish a seasonal dollar figure for it, because that depends on the voltage configuration an installer selects and we have no measured figure for a specific installation. What is safe to say is that the relationship on the portable side - 280 W to boil against 17 to 30 W not to, roughly a factor of ten - is the same physics at a larger scale. The portable arithmetic is on running cost.
Consumables and maintenance
| Evaporative | Steam | |
|---|---|---|
| Consumable | Water panel | Steam canister |
| Interval published | Annually (Model 400: twice per season) | Every year (Model 80 canister) |
| Other scheduled work | None stated | Electrode wires every 3 years, by a licensed contractor |
| Standing water | None - it drains | None - it boils and drains |
| Water use beyond evaporation | Yes, to drain | Yes, to drain |
Both avoid the standing-water problem that dominates portable humidifier ownership, which is the shared advantage of the ducted category and the reason neither needs the EPA's every-third-day routine. The steam unit's electrode-wire service is a genuine extra: Aprilaire states it as a three-yearly job for a licensed contractor, which is a recurring professional visit rather than a part you swap.
How you buy them
Worth stating plainly because it is not obvious from the specification sheets. Neither Aprilaire whole-house unit is an add-to-cart purchase on the manufacturer's own store. Both the Model 700 and the Model 800 route to a "Find a Pro" contractor network rather than a checkout.
The evaporative models are, however, widely stocked by retailers and trade suppliers, so they are genuinely purchasable if you are installing one yourself. We did not find equivalent consumer retail availability for the steam model, which is consistent with it being a contractor-installed product with a voltage configuration chosen at install time. If you are pricing a steam unit, expect the conversation to start with a contractor rather than a cart.
The decision
| If | Then | Because |
|---|---|---|
| You have a gas furnace that runs regularly in winter | Evaporative | Cheapest to run, cheapest consumable, and the furnace air is free energy |
| You have a heat pump, or heating cycles rarely | Steam | Evaporative output is tied to furnace runtime and lower supply temperatures |
| You need more than about 20 gal/day | Steam | The fan-powered evaporative range tops out around 18 |
| You are in a very dry climate with high humidity targets | Steam | Independent of furnace runtime, so it can hold a target through mild spells |
| Electricity is expensive where you are | Evaporative | A steam unit is an electric boiler and the tariff compounds all season |
| You have no ducted forced-air system at all | Neither | Both need a duct. See whole house vs room |
For most houses with a working gas furnace, evaporative is the right answer and the cost difference is not close. Steam earns its place in the specific cases above, and in those cases it earns it decisively rather than marginally.
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
What is the difference between a steam and an evaporative whole house humidifier?
Where the evaporation energy comes from. An evaporative unit uses the furnace's own warm air blown across a wet water panel, so it only works while the furnace is running. A steam unit boils water electrically and injects vapor into the duct, so it runs independently of the heating.
Is a steam humidifier better than evaporative?
Only in specific cases. Steam reaches roughly double the capacity - Aprilaire publishes up to 34.6 gallons a day against 18 for its largest fan-powered evaporative unit - and it works when the furnace is not running, which matters with a heat pump or in a house that heats infrequently. For a typical gas-furnace home, evaporative is much cheaper to run and to maintain.
Do steam humidifiers use a lot of electricity?
Yes, relatively - a steam humidifier is an electric boiler, and Aprilaire describes its output as varying with voltage and current draw, which means capacity and consumption are the same dial. We do not publish a seasonal figure because it depends on the voltage configuration chosen at install and we have no measured figure for a specific installation.
How often do you service a steam whole house humidifier?
Aprilaire states the steam canister and O-ring should be replaced every year, and the electrode wires every three years by a licensed contractor. An evaporative unit's water panel is annual on the same maintenance page, with no professional visit stated.
Can you buy a whole house humidifier directly?
Not from Aprilaire's own store - both the evaporative Model 700 and the steam Model 800 route to a contractor network rather than offering an add-to-cart. The evaporative models are widely stocked by retailers and trade suppliers; we did not find equivalent consumer retail availability for the steam model.
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 800 steam humidifier - manufacturer spec page (retrieved September 1, 2026)
- Aprilaire Model 700 - manufacturer spec page (retrieved September 1, 2026)
- Aprilaire Model 500 - manufacturer spec page (retrieved September 1, 2026)
- Aprilaire Model 400 - 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)
- 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)
- US Energy Information Administration - Electric Power Monthly, Table 5.3: average residential price 18.34 cents per kilowatthour, United States, June 2026
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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.