AprilAire Model 400 m Water Saver 17 Gal. for up to 5,000 sq. ft. Whole-House Evaporative Humidifier With Manual Control

Item # 312148211 | AprilAire Part # 400M | UPC Code 686720404009 | UNSPSC Code 40101903 | Catalog Page #676
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Product Overview

AprilAire helps make your home a Healthy Air environment with the Model 400M 17 Gal. Water Saver Humidifier. This whole-house humidifier is designed for homes up to 5,000 sq. ft. delivering optimal relative humidity to balance out the dry, hot air created by furnaces. Its innovative design uses 100% of the water that enters the system, utilizing a unique evaporative process that's perfect for homes with a septic system. Plus, it saves on water and energy costs. The included manual humidistat lets you control the humidity level throughout your home. While balanced humidity exists between 40-60%, it's important to remember that outdoor temperature and other home factors will impact what relative humidity level is attainable and recommended for your house. You'll enjoy balanced humidity thanks to the evaporative process, which works by passing hot, dry air from your furnace over the interior water panel to add moisture before returning the humidified air into your home using the existing blower fan in your HVAC system. The water panel is essential to the process, ensuring the removal of impurities from the water and providing uniform, high evaporation for whole-house humidification. AprilAire invented the whole-house evaporative humidifier in 1954 and this unit is designed utilizing global components. It offers multiple options for installation, making it simple to experience the benefits of balanced humidity throughout your living space.

  • Water panel removes impurities before adding moisture to the air (use genuine AprilAire 45 water panel for twice annual replacement)
  • Adds up to 17 Gal. of moisture per day to create balanced humidity
  • Helps preserve wood floors, cabinetry, furnishings and other items susceptible to dry air
  • Helps minimize the formation of bacteria, viruses, fungi and dust mites that thrive in low humidity
  • Helps reduce the incidence of respiratory infections and symptoms related to allergies and asthma
  • Uses 100% of water passing through the system-ideal for customers with septic systems
  • Water-saving design reduces energy and water costs
  • Delivers precise control, sufficient humidification capacity, trouble-free performance and minimal maintenance
  • Included manual humidistat monitors your home's air and provides precise control
  • Onboard sensor actively measures RH throughout your home and turns on the humidifier when needed
  • Designed to prevent overflows and automatically shut off to preserve operation
  • Detailed installation instructions included in manual
  • Works for homes with ducted heating systems
  • Designed and assembled in utilizing and global components
  • Included in the box: 400 humidifier, manual humidistat control, 24-Volt transformer, saddle valve, 45 water panel, installation instructions
  • 5-year warranty


Certifications and Listings
No Certifications or Listings
Control Type
General Color Family
Humidification Method
Humidifier Features
Adjustable Humidistat, Automatic Moisture Control, Automatic Shut Off, Filter Included
Humidifier Tank Capacity (Gallons)
HVAC Product Type
Manufacturer Warranty
5 years from installation
Maximum coverage area (sq. ft.)
Pack Size
Product Depth (in.)
Product Height (in.)
Product Weight (lb.)
Product Width (in.)


5 years from installation