Quantifying energy losses in hot water reheat systems

•New method to estimate energy use and distribution losses in hot water reheat systems.•Accurate to within 14% as assessed in case study of 11,000 m2 office building.•Gas to intentional reheat energy conversion shows 79% loss, incl. 44% distribution loss.•High boiler losses for these systems in practice due to ultra-low part load operation.•Electric reheat and PV cheaper and more efficient than current practice in many cases.