Humidifier sizing, in gallons per day
What size humidifier you need, derived from manufacturer figures and shown as arithmetic you can redo. Includes the calculator and the ceiling-height correction.
Sizing. Cleaning. Filter costs.
Humidifiers, sized in gallons per day
Trusted the only way a new publication can be: the sizing math, the filter-cost arithmetic and the source of every figure are all shown. We have tested nothing, and we say so on every page.
Everyone here says they tested twenty humidifiers
We have not tested any, and we say so. What we did instead: compiled 64 published specifications from 11 manufacturers’ own pages, computed each unit’s daily output against the floor area it claims to cover, totaled the filter costs, and linked every source so you can check us. The whole method is on how we pick, including what it cannot tell you.
- Units we claim to have tested
- 0
- Free products accepted
- 0
- Sponsored placements
- 0
- Sourced figures compiled
- 64
Start where your question is
How to clean a humidifier
The full cleaning method, the EPA's stated intervals, and the two corrections this category keeps getting wrong.
What a humidifier costs to own
Cost of ownership: filter intervals, electricity at a cited tariff, and five-year totals with every step of the arithmetic shown.
Types of humidifiers
The four humidifier designs, compared on the attributes that genuinely differ, with a decision table rather than a survey.
The best humidifiers
The master roundup: every unit in our set, with its output computed against its coverage claim and a stated reason to skip it.
The picks, with today’s prices
We show a live price when we have one and the words “Check price” when we do not. We never print a number we cannot currently verify, which is why these read the way they do today. Every link is an affiliate link and we earn a commission at no extra cost to you. Full disclosure.
Best for large rooms
Best humidifiers for large rooms
Large-room picks, chosen on whether the published output reaches the requirement rather than on what the box claims.
Top pick: Vornado Evap40 · 4.0 gal/day
Easiest to clean
The humidifiers that are easiest to clean
Units designed around the maintenance problem: dishwasher-safe parts, wide openings and drying cycles, on published manufacturer features.
Top pick: Honeywell HCM350 Germ Free Cool Moisture · 1.0 gal/day
Best filter-free
Best filter-free humidifiers
Filter-free ultrasonic picks, with an honest account of the white-dust trade that comes with having no wick.
Top pick: Levoit Classic 300S · 0.63 gal/day
Work out your number
Divide your room’s floor area by 296 and correct for ceiling height. That rate is derived from Aprilaire’s own published capacity-and-coverage pairs, which are the only ones in our set tied to the residential sizing standard - the full derivation is on gallons per day.
Size my room
You need about
1.0gallons per day
The working
- 1. Volume = 300 sq ft x 8 ft = 2,400 cu ft
- 2. At an 8 ft ceiling that is 300 sq ft of equivalent floor area
- 3. 300 ÷ 296 sq ft per gal/day = 1.0 gal/day
The rate in step 3 is derived from Aprilaire’s own published capacity-and-coverage pairs, which are the only ones in our set tied to the residential sizing standard. It describes a tightly constructed home. Nobody publishes a multiplier for a drafty one and we have not invented one, so treat this as a floor rather than a ceiling. Where the number comes from.
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