Heterogeneous photocatalysis, also referred to as photocatalytic oxidation, or PCO, is an emerging advanced oxidizing technology that offers many application opportunities in the HVAC industry. One of the most highly anticipated uses is in providing energy-sensitive solutions to IAQ challenges. A number of system design considerations should be given by the specifying engineer toward maximizing the success of deploying PCO technology in building HVAC designs. This article presents several of those considerations to familiarize system designers with the process of applying PCO technologies.