October 29, 2012

This guideline pertains to design and application guidance for combination space and tankless domestic hot water (DHW) heating systems (combination systems) used in residential buildings, based on field evaluation, testing, and industry meetings. As residential building enclosure improvements continue to drive heating loads down, using the same water heating equipment for both space heating and domestic water heating becomes attractive from an initial cost and space-saving perspective. This topic is applicable to single- and multifamily residential buildings, both new and retrofitted. Before committing to wide-scale implementation of such combination space and domestic water heating systems for high performance buildings, whether new or retrofit, design decisions and site conditions affecting performance, maintenance, and occupant acceptability should be well understood. Current performance rating procedures for this type of hot water heating system and its many variants are inadequate to provide convincing prediction of estimated savings. In order to be assured of meeting the Building America savings goals, and the persistence of those savings after installation, continued sharing of lab and field testing results is needed.


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