An analysis has been made to predict the number of fan/pump cycles, the number of burner/gas-valve cycles, and the burner operating hours that combination (combo) heating systems utilising a gas-fired water heater may experience in a typical year of operation. The cycling characteristics were determined for reasonable ranges of climates, equipment sizing ratios, and hot water usage rates. The climatic data represented the six heating regions of the US Department of Energy (DOE) that are used for rating the heating performance of appliances. The combination heating system cycling characteristics were predicted for a wide range of variables utilising a bin calculation method similar to that used for evaluating furnace or heat pump performance. An understanding of these operating parameters will give those who design and install combo systems important insights into system and component cycling characteristics.

KEYWORDS: cyclic, properties, components, gas fired boilers, combination boilers, boilers, space heating, gas fired, water heaters, operations, climate, performance, appliances, heat pumps.