Condensing boilers, while commonly installed for heating hot water applications, often fail to deliver their inherent efficiency advantage because of deficiencies in the system design, start-up, and operation. Condensing or “high efficiency” boilers are constructed to allow them to operate with lower water temperatures than traditional boilers. This allows condensing boilers to extract more of the useful (latent) energy from the fuel source (typically natural gas or propane) than traditional, non-condensing boilers can use. For condensing boilers to realize their potential for increased efficiency, they must be applied and operated in a manner that allows their combustion gases to condense. Designers and facility operators interested in achieving the efficiency potential of their condensing boilers need to have an understanding of how to design and implement the appropriate system arrangement and control parameters for their boilers.
In this article we will describe how to properly apply a heating hot water reset schedule to maximize the benefits of a condensing boiler. This article provides example calculations for a finned tube (i.e. traditional perimeter heating) system, yet the concepts may be applied to VAV terminal unit heating as well.