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Aprilaire 400 Bypass Humidifier for use with Residential or Commercial Heating Equipment

Price: $236.78
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The Model 400 bypass humidifier is a high-capacity, water-conserving humidifier (0.70 gallons evaporated per hour) incorporating a water recirculation system for use where drain facilities are not accessible or available.

It uses 100% of the water that goes into the unit.

Automatically adjust humidity levels based upon outside air temperature with remote sensing bulb.

Humidifies up to 4,000 square feet if your home is tight in construction.

The Model 400 is also a good choice for homes with heat pumps.

Due to lower plenum temperatures the unit should be connected to your hot water supply line.

Also included are a saddle valve, automatic humidistat control w/ sensing bulb and installation and operating instructions.



Loose house (2 air changes/hr.)1,000 SQ. FT

Average house (1 air change/hr.)2,000 SQ. FT
Tight house (
• air change/hr.)4,000 SQ. FT

Bypass There are two basic humidifier types: bypass and power fan. Each simply uses a different method to move air through them. Power fan humidifiers use a 110 volt fan to move air through them. Bypass humidifiers do not have a fan, but instead require a 6
• duct to be connected to the side and then to the opposite air duct system from the humidifier.

That means for bypass models that if the humidifier is installed on the supply plenum, the 6
• duct will connect to the humidifier and the return plenum, and if the humidifier is installed on the return plenum, the 6
• duct will attach to humidifier and the supply plenum.

Both humidifier types
• bypass and power fan
• will provide the same benefits to you. The only difference is the technology used to do so.

The advantage to power fan models is since they do not require additional ductwork, they can be installed faster and in tighter spaces.

The advantage to bypass models is that they cost a bit less.
Remote Sensing Bulb Included A remote sensing bulb is a small (about

• round) sensor that mounts outside the home and connects by light gauge wire (18 to 22 gauge, 2-conductor) to the humidifier controller.

This sensor provides temperature readings to the computerized controller which allows the humidifier to automatically adjust humidity levels in the home based on outside air temperature.

Aprilaire brand humidifiers include a remote sensing bulb in the box with the purchase. Honeywell brand humidifiers do not include remote sensing bulbs, but offer such as an additional purchase option.

Both brands allow for humidifier operation without the use of the sensor should you choose to not install such.

Dimensions: 14"W x 15-7/8"H x 10-3/8"D

Electrical: 24V-60Hz-0.5 AMP

Included: No: Not included: 1/4" copper tubing for water line, 6" round ducting & elbow for bypass air, 2-conductor 18 to 22 gauge wire.

Includes a 110v to 24v transformer.

I called trying to find out what happened to the rest of my order and was surprised to hear a warm and kind voice willing to do whatever it takes to find answers and follow through with her promise. Amanda is an asset worth holding on to and a credit to your company. She was very professional, helpful and courteous while assisting me with my order. I would most definitely assign her an A+ in customer service."
Donald "Brad" Thomas

I would like to thank you for your hard work in getting us our part in a timely fashion. You were very helpful and you understood the severity of the situation and did a wonderful job in getting the part to us. Thanks again and please share this with your boss! You were outstanding!"
Todd Mills

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