Aprilaire 400 Humidifier, Whole House w/ Auto Digital Control, 0.7 Gallons/hr

Brand: Aprilaire
Model: 400
Condition: New
Warranty: 5 Years
SKU: 887451
4.35 (1 Review)
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Aprilaire 400 Whole House Humidifier

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The Aprilaire 400 humidifieris a 24 volt drainless whole-house humidifier with automatic digital control. The Aprilaire state of the art humidifier utilizes gravity to pull water in and disperse it into the air, utilizing 100 percent of water to add moisture to your air. By evaporating up to 0.7 gallons of water per hour, you’ll never have to experience the discomfort of dry air again! Best of all, the wide ranging effects of this device can reach all rooms in a tightly constructed home of up to 4,000 square feet!  If you are all about water conservation or live in an area where standing water can become a problem, don’t wait another day to get the Aprilaire 400 Whole House Humidifier. It not only recycles water cleanly into the air, but can help eliminate water where draining is not available.

The Aprilaire 400 humidifier does not require much maintenance at all.  You should visually inspect the unit every 500 hours, more frequently during heavy use.  Inspect the plumbing and water lines for cracks or leaks and replace as needed.  The one item that does require to be replaced is the water panel.  The water panel should be replaced annually during regular use, and every six months during heavy use.

Are you tired of dry skin, splitting or cracking on your hard wood floors or trouble breathing in your home? These can all be signs of a lack of moisture within your airflow, meaning that you and your family will benefit greatly from the Apriliare 400.


Heat pumps: Aprilaire Model 400 can be installed in heat pump applications. However, due to the fact that heat pumps deliver lower temperature air to the home than gas furnaces, evaporation will be approximately 60% of rated capacity. (With other Aprilaire models hot water can be used instead of cold to maximize evaporation. However, due to the nature of the wicking water panel in the Model 400 hot water provides no extra benefit.

  • Automatic Digital Humidifier Control
  • Evaporating Capacity of 0.70 Gallons Per Hour
  • Humidifies Up to 4,000 Square Foot
  • Ideal for Tight Construction Homes
  • Provides Service, Temperature, Humidity Statistics
  • Minimal water usage
  • Electrical Data: 24V-60Hz 0.5 AMP
  • Plenum Opening (inches): 10W x 12-3/4H
  • Sq. Ft. Area (air changes/hr.): 1,000 loose house (2) / 2,000 avg. house (1) / 4,000 tight house (1/2)
  • Unit Size (inches): 15-3/8W x 15-3/4H x 10-1/4D 6" dia. round opening
  • Water Evap Rate: 0.70 gph
Aprilaire 400 humidifier Must be PROFESSIONALLY INSTALLED to receive the 5-year warranty through Aprilaire. Warranty is void unless humidifier is installed by qualified HVAC due to possible incorrect installation.
Customer Reviews

Trouble deciding between the Aprilaire 400 and 600

I had some trouble deciding between the Aprilaire 400 and 600 but opted for this one because it's automatic (didn't want to adjust the humidity level every time the RH changes). I also like that it humidifies the air even when the furnace is turned off. Great humidifier, I am glad I picked it.


on 07-10-2014 by Billy

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Questions & Answers

can this aprilaire 400 be used on a gas (propane) furnace that is in an unheated attic?? is there a humidifier made for such an application

by Lawrence D. from central new jersey on 03-10-2013

The 400 can be used on a gas furnace with out any issue when installed correctly.

on 03-12-2013

I am looking to replace my existing Aprilaire 400A and understand this is it's replacement unit with additional benefit. My question is when I installed the first one my opening to the cool side return was 11"H X13.5"W. In looking at the specs for this unit the opening is smaller. My question or concern is how to handle that delta? Do I seal the first opening and start over or look to reduce the existing open to make the specs for this new model?

by Kevin M. from New Jersey on 10-14-2012

The Aprilaire 400 is the same model as the 400A, however, it was simply re-named. This is not a replacement to a discontinued item.

on 10-31-2012

is there an on/off switch for the transformer on an 400 humidifier

by PASQUALE S. on 10-12-2012

No, this unit requires 24V connection. Attempting to operate this at line voltage (120V) will damage the unit. Do not attempt this, the transformer is for your own safety.

on 10-16-2012
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