Presents the results of a study into the transient operating characteristics and combined annual efficiencies of several different types of gas-fired combination space/water-heating systems. Transient characteristics were measured under cycling conditions representing both average and peak winter operation. Annual system efficiencies were calculated using the proposed ASHRAE Standard 124P procedure for rating these appliances and compared to measured efficiencies under cycling test conditions. States the test results show that conventional gas-fired water heaters are capable of supplying both domestic hot water and space heating loads even during peak winter design conditions, when the components of the combination system are properly sized. The water heater designs generally provided good temperature stratification with an adequate supply of hot water. Under all but the most severe conditions the warm air supply temperature were in the range of 100 to 110degF (38 to 43degC) with 70degF (21degC) return air. There was good agreement between the results from ASHRAE-124P tests and the measured-use tests in terms of recovery efficiency, energy factor, heating efficiency and combined annual efficiency for four different combination heaters.

KEYWORDS: Operations, efficiency, USA, space heating, domestic, hot water supply, warm air heating, standards, testing, gas heating, combination boilers