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Enhanced humidity control options with Aprilaire "A" series humidifiers

Aprilaire introduced a new digital control system (AKA humidistat) during the last humidification season (winter of 2007-2008) which offers more accuracy and information to the homeowner than ever before.  This article will explore the features and benefits of this new humidistat.

These Aprilaire humidifiers will include the new automatic control

Model 700A Powered Humidifier
Model 600A Bypass Humidifier
Model 500A Bypass Humidifier
Model 400A Bypass Humidifier

Theory of Operations:

The optimum levels of relative humidity in your home fluctuate with the changes in outdoor temperature. The Aprilaire automatic humidifier control continually monitors and responds to both outdoor temperatures and indoor relative humidity, delivering optimum levels of humidity throughout your home. You never have to monitor your settings or wait until you feel uncomfortable. The automatic set-it-and-forget-it control keeps your home's humidity level exactly where you want it.

The figure above shows the old #56 control (left) and the new # 58 automatic digital control (right).  One glance reveals a substantial change in control appearance.  Truth-be-told - the old and new controls are functionally very similar.  In both cases:

* The control mounts on the return ductwork of the furnace
* The control automatically regulates humidity based on the outdoor temperature (each requires that an outdoor temperature sensor is mounted outdoors)
* The control can be converted to manual operation by connecting an included manual mode resistor

So, what's new about the updated #58 control?

* A backlit digital display provides the current humidity level in the home
* A green light shows when the humidifier is running
* A yellow light monitors run time and lets you know when it's time to replace your humidifier water panel
* A red light shows when when there is a problem with the unit

In short, this new control gives more humidification status information to the homeowner than other controls on the market.

Tech Talk:

If you have a professional contractor to install your humidifier (recommended), you do not need to read this section of the article.  With the changes / enhancements to the # 58 control come a few new installation requirements.  The old control was able to work with a switched source of 24 VAC power.  The new #58 control requires a constant supply of power to light the display and function properly.  Additionally, the new control has new wiring requirements in place to "prove" that the HVAC fan is running OR the furnace itself is running (obviously, you don't want water flowing through your humidifier if there is no way to distribute the humidified air). 

Bottom line - the wiring is a bit more complicated with the new control.  We have created a support addendum to help with pre-sales installation questions.