CO2/VOC sensors monitor a room or return air duct, then send two separate readings to the hvac system, which makes necessary ventilation adjustments. Unlike most CO2 sensors, these units employ a patented photo-acoustic technology that provides more stable measurement and requires no calibration, which in turn means fewer maintenance calls, says the company. A separate ventilation-demand calculator is also available that takes both signals, weights them, and outputs one combined signal.

Staefa Control System, 1000 Deerfield Parkway, Buffalo Grove, IL 60089; 800-735-4822; 847-215-8204 (fax); (Web site).