The Honeywell H8908B Humidistat and H8908A/B models are designed for low-voltage control of whole-house humidifiers, dehumidifiers, and ventilators in central heating and air conditioning systems. These devices offer precise humidity management through a snap-acting, dust-proof SPST switch and are suitable for both wall and duct mounting. This article provides a detailed, fact-based guide to the installation process, operational adjustments, and essential safety considerations based on official documentation provided by Honeywell.
Overview of the H8908 Humidistat
The H8908 family includes the H8908B Humidistat and the H8908C Dehumidistat, both of which are low-voltage humidity controllers. These units are engineered for automatic control of humidifiers and dehumidifiers, respectively, and are typically used in conjunction with central HVAC systems. The devices feature a snap-acting switch and are compatible with both wall and duct mounting options. The design of the H8908 aligns with the T8600 series of Honeywell thermostats, enabling a cohesive aesthetic in HVAC control systems.
A mounting template is included with the H8908 for wall mounting, particularly for use alongside the T8600 thermostat. However, the device can also be installed at any convenient location in the living area or equipment room. It is important to note that the H8908's electrical connections are separate from the thermostat, and therefore, must be configured independently.
Installation Requirements and Safety Precautions
Before beginning the installation of the H8908 Humidistat, several key requirements and safety precautions must be observed to ensure proper functionality and user safety.
Qualified Installer Requirement
According to the installation instructions provided, the H8908 must be installed by a trained and experienced service technician. This requirement ensures that the installation is performed correctly and safely, minimizing the risk of damage to the device or electrical hazards.
Power Supply Safety
A critical safety warning is included in the documentation: the power supply can pose an electrical shock hazard. Therefore, it is imperative to disconnect the power supply before beginning the installation process. This precaution is emphasized in both the H8908B and H8908A/B installation instructions.
Compatibility and Ratings
Before installation, it is essential to verify the product's suitability for the intended application by checking the ratings provided in the instructions and on the device itself. This ensures that the H8908 is compatible with the system in which it will be used and can function without risk of malfunction or damage.
Mounting Options and Procedures
The H8908 Humidistat offers two primary mounting options: wall mounting and duct mounting. Each method involves specific steps and considerations to ensure the device is installed correctly.
Wall Mounting
For wall mounting, the H8908 is designed to be installed near the T8600 thermostat. The included mounting template assists in aligning the humidistat with the thermostat. The following steps outline the wall mounting procedure:
- Hold the mounting template next to the T8600 thermostat and select the desired side for the H8908 installation.
- Mark the hole locations for the two mounting screws and the wiring hole on the wall.
- Secure the H8908 to the wall using the included screws, ensuring the device is positioned in an area with average room temperature and average relative humidity.
It is important to mount the device in a location that is representative of the typical indoor environment to ensure accurate humidity readings.
Duct Mounting
For duct mounting, the H8908 can be installed on the surface of a duct. The procedure includes the following steps:
- Choose a suitable location on the duct for installation.
- Apply the mounting template to the duct and mark the hole locations for the mounting screws.
- Cut the duct along the marked lines using metal shears or tin snips.
- Run two-fan, low-voltage wiring to the selected mounting location on the duct.
It is recommended to use 18-22 gauge wire for the electrical connections and to leave approximately 6 inches of wire to ensure proper connection to the humidistat.
Remote Mounting in Living Areas
In cases where duct or wall mounting is not feasible, the H8908 can be installed in a convenient location within the living area. This method, referred to as remote mounting, allows for greater flexibility in positioning the device. The following considerations apply:
- The location should ideally reflect the average temperature and humidity of the living space.
- The humidistat should be mounted away from direct sources of heat or moisture to avoid inaccurate readings.
- The wiring must be run from the humidifier or dehumidifier to the remote mounting location, following the same electrical guidelines as for duct or wall mounting.
Electrical Connections and Wiring
The H8908 Humidistat requires a low-voltage wiring connection, typically used for 24V AC systems. The wiring should be run from the humidifier or dehumidifier to the humidistat, ensuring a secure and reliable connection.
Wiring Requirements
- Use 18-22 gauge wire for all electrical connections.
- Ensure that the wire is properly insulated and rated for the intended application.
- Leave approximately 6 inches of wire at the humidistat for connection purposes.
The humidistat’s wiring is separate from the thermostat, so it must be connected independently to the control system. This ensures that the humidistat can operate without interference from other components of the HVAC system.
Post-Installation Checkout and Operation
After installation, it is essential to perform a checkout to verify that the H8908 is functioning correctly. The following steps outline the checkout procedure:
- Turn the H8908 dial to the “ON” position.
- Listen for an audible click, which indicates that the humidistat has engaged.
- Observe the humidifier to confirm that water is beginning to flow, indicating that the system is operational.
If the humidistat does not respond as expected, recheck the installation, including the wiring and mounting location, to identify and resolve any issues.
Humidity Control Adjustment
Once the H8908 is installed and operational, the homeowner is responsible for adjusting the setpoint to maintain optimal humidity levels. This adjustment is necessary to prevent condensation on cold surfaces, such as windows, particularly during temperature changes.
The setpoint should be adjusted according to the outdoor temperature. As the outdoor temperature fluctuates, the ideal indoor humidity level may also change. It is important to monitor the indoor environment and make adjustments as needed to ensure comfort and prevent damage caused by excessive humidity or dryness.
Maintenance and Troubleshooting
Although the H8908 is designed for long-term reliability, periodic maintenance and troubleshooting may be necessary to ensure continued performance. The following tips can help users identify and address common issues:
- No Power to the Device: Check the power supply and ensure that the wiring connections are secure and free from damage.
- Device Not Responding: Verify that the humidistat is set to the correct mode (humidistat or dehumidistat) and that the setpoint is properly adjusted.
- Inaccurate Readings: Ensure that the device is mounted in a location that is representative of the indoor environment and not affected by direct sources of heat or moisture.
If issues persist, it is recommended to contact a qualified HVAC technician for further assistance.
Conclusion
The Honeywell H8908 Humidistat is a reliable and effective solution for managing indoor humidity levels in central HVAC systems. With its low-voltage design, snap-acting switch, and compatibility with both wall and duct mounting, the H8908 provides a versatile and accurate means of controlling whole-house humidifiers and dehumidifiers. By following the installation guidelines outlined in the official documentation, users can ensure a safe and effective installation that supports optimal indoor air quality and comfort.