Published on January 09, 2026 by Claudio Cabete
As part of my ongoing work on a custom HVAC controller and energy efficiency optimizer, I recently made a small but impactful upgrade: adding intelligent control to my whole-house humidifier.
While humidifiers are often treated as simple “set and forget” accessories, the way they are controlled can have a surprising effect on both water usage and heating efficiency.
This post walks through the original setup, the problems it created, and how I improved it using a spare relay on my custom controller.
The humidifier in question is an Aprilaire 550, using Honeywell HC22P humidifier pads. Like many residential installs, it was wired in a very common and straightforward way:
Water source → Manual shutoff valve → Electric solenoid valve → Humidifier
The solenoid valve was controlled directly by the humidifier’s own humidity sensor. When the furnace turned on and the sensor detected that the air was too dry, the solenoid energized and water flowed continuously over the humidifier pad for the entire heating cycle.
This setup is simple, reliable, and effective at increasing indoor humidity — which is why it’s so common.
Unfortunately, it also has some downsides.
While the original design works, it introduces two significant inefficiencies:
Once the humidifier pad is saturated, additional water provides diminishing returns. In practice, much of the water simply drains away unused.
Over the course of a heating season, this adds up to a surprising amount of wasted water.
The water supplied to the humidifier is cold. Continuously dripping cold water into the system during a heat cycle means the furnace must work harder to maintain temperature.
In other words, the humidifier was actively working against the furnace from an efficiency standpoint.
My HVAC system is already managed by a custom controller built around a Raspberry Pi Pico W, paired with an 8-relay daughter board.
Since I had spare relay capacity, it made sense to bring the humidifier under the same intelligent control as the rest of the system.
Instead of letting the humidifier sensor directly control the solenoid valve, I inserted one of the controller’s relays into the circuit.
This allowed the system to make smarter decisions based on:
Here’s how the improved system works:
In effect, the system now pulses water onto the pad instead of running continuously.
This approach delivers several benefits:
The pad stays properly wetted, but excess runoff is dramatically reduced.
Less cold water means less thermal loss during heating cycles.
Humidity control is now part of the overall HVAC optimization strategy instead of operating independently.
The Aprilaire 550 and Honeywell HC22P pads remain unchanged — all improvements are done through smarter control.
This upgrade is a good example of how small logic changes can produce meaningful efficiency gains. By integrating humidifier control into the broader HVAC controller, the system becomes more efficient without sacrificing comfort.
It’s also a reminder that many “dumb” accessories in home HVAC systems can benefit from even modest levels of automation.
More improvements are coming as I continue refining this controller — stay tuned.
— homatica.cc