Lennox 21Z09 Sensor Kit

The Lennox 21Z09 Enthalpy Sensor Kit (also identified as 603364-35) is a critical diagnostic and control component for commercial HVAC rooftop units. Operating as a high-precision dual-sensing device, this enthalpy sensor replacement monitors both sensible temperature and relative humidity to determine the total heat content of the air. This data is essential for economizer air-side control, allowing the system to utilize outdoor air for free cooling when conditions are favorable, significantly reducing mechanical cooling load. Designed for Lennox L Series, Landmark, and T-Class packaged units, this kit ensures your economizer logic functions with maximum thermodynamic accuracy.

This HVAC economizer sensor utilizes high-sensitivity thermistor and humidity elements to calculate the enthalpy of a gas sample effectively. In differential enthalpy sensing applications, two kits are required to compare return air and outdoor air conditions. By integrating this Lennox 21Z09 into your preventive maintenance or repair workflow, you ensure consistent basement-to-rooftop air quality control and energy efficiency compliance. Its rugged construction is built to withstand the demanding conditions of industrial air streams, ensuring long-term HVAC part compatibility across various standard and high-performance economizer configurations.

• Dual Measurement Precision: Simultaneous monitoring of latent and sensible heat for accurate enthalpy calculations.
• Optimized Free Cooling: Enables economizer logic to reduce compressor wear and energy consumption during favorable outdoor conditions.
• Direct Compatibility: Engineered for seamless integration with Lennox LGM/LCM, LGH/LCH, and KG/KC/KH series units.
• Industrial Durability: Robust housing designed for reliable performance in high-velocity duct environments.
• Differential Sensing Capability: Supports advanced dual-sensor setups for more precise energy management (requires two kits).

What is the difference between single and differential enthalpy sensing?
Single enthalpy sensing uses one 21Z09 sensor to measure outdoor air against a fixed setpoint. Differential sensing uses two sensors to compare outdoor air directly against return air, allowing for more precise economizer performance in humid climates.

Is this kit compatible with high-performance Siemens controllers?
Yes, the Lennox 21Z09 is compatible with Siemens-based high-performance economizer systems used in many KG/KC/KH and ZG/ZC/ZH commercial units.

What is included in the sensor kit?
The kit typically includes the 603364-35 sensor, required wiring harnesses (P104/P105), mounting brackets, and hardware for standard installation.

This item is not eligible for free shipping.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.