From 12.43 to 20.88 in. The self-contained 300 is shortest but 22.07 in wide; the steam 800 and 865 are tallest but 7.13 in wide.
So a low space favors the 300 and a narrow one the steam pair. Your installer picks the type.
Disclosure: Havenraft participates in the Amazon Associates Program and may earn commissions from qualifying purchases through product links on this site.
With no preferences selected: AprilAire 300 Self-Contained Evaporative Humidifier is one option to compare.
Your choices are compared with each model’s product details. A missing or conflicting value stays unknown and cannot satisfy a choice you select. The starting order helps you browse; it does not rate real-world performance.
Source dates appear with each link below. A source date does not confirm today's price or stock.
AprilAire 865 Steam Humidifier with Fan Pack: Source 1 ↗ · September 26, 2026
Evaporative output needs the maker's operating conditions
AprilAire's Small Bypass has a rated output of 12 gal per day, while its Fan-Powered Evaporative models are rated at 21 gal per day. Those endpoints cover 8 units with output data. The steam models have no output value here and cannot be placed below the evaporative units on that basis.
Humidifier type changes the installation question: bypass evaporative, fan-powered and steam models need their own installation drawings. This is a comparison of AprilAire's ratings without measuring humidity delivery in a house. Read the rating conditions and have the proposed system sized for its installation rather than treating a rated daily volume as a home-sizing formula.
The narrow steam body still needs a complete installation plan
Body widths range from 7.13 to 22.07 in. AprilAire's steam units sit at the narrower end, while its Self-Contained Evaporative unit sits at the wider end. Body height and depth, connection space and service access must all come from the drawing for the actual model.
AprilAire offers manual and automatic control packages, including different versions of its Large Bypass and Fan-Powered units. Verify which control comes in the order, the water and electrical connections, and the service instructions. A small enclosure does not settle whether the installation is suitable.
Before you buy
Can this page size a humidifier for my house?
It can't. AprilAire's ratings, from 12 gal/day on the 500 to 21 gal/day on the 720A and 720M, hinge on installation and operating conditions, so your installer has to assess the home, the HVAC equipment and the installation conditions before choosing a capacity or type. The body sizes here also leave out service space, duct openings and fan-pack dimensions.
Why is there no output figure for the steam models?
AprilAire's steam output changes with the unit's voltage and current configuration, so the 800 and 865 have no single number here rather than one that would hide that difference. Their bodies are also the narrowest here, about a third as wide as the 300.
What's the difference between the A and M versions?
The control in the box. By AprilAire's in-the-box lists, the 620A and 720A come with an automatic control and the 620M and 720M with a manual one, on matching bodies and ratings. The 620A's page title says Manual, but its heading, feature copy and the Model 60 automatic control in the box all point to automatic.
Can I buy these directly from the linked pages?
AprilAire's pages send consumers to its nationwide professional network. They give exact model details but state no dealer stock or installed price.
AprilAire 300 Self-Contained Evaporative HumidifierView at AprilAire
