Demand control ventilation (DCV) systems use sensors to control ventilation air to a space or spaces based on the estimated number of people present. Though the technology has been around for some time and has multiple theoretical benefits, less is known about its performance in real systems, especially complex multizone ones. A field study was implemented to fill this knowledge gap. Study results show that DCV does save significant energy (primarily the fuel used for heating), and is generally cost-effective for most owners. It also demonstrated improvement in systems through recommissioning, but showed that greater deficiencies are found in the design phase for this technology. Based on field observations, best practices for both design and commissioning are also shared.