The paper deals with many issues concerning hybrid water heating system based on the cooperation of thermal solar collectors, economizer using gas tube heaters' exhaust and gas boiler, which has not been recognized in literature enough. The energy analysis for such hybrid system has been performed after optimal system components sizing. Two analysis methods for hybrid system are discussed: the authors own hour-by-hour method and per-moth method suitable for engineering design. The operation time of the peak source and the temperature in the hot water tank during the year were checked. The annual energy shares of the particular sources were determined during analysis. The economizer gave 18.6% (per-month method) or 17.5% (hour-by-hour method) of energy; 62.0% (per-month method) or 60.0% (hour-by-hour method) of energy had been obtained using 68 solar collectors, but using 34 solar collectors the gains were 37.5% or 40.7% (per-month or hour-by-hour method). The design guidelines for engineers were specified and provided. The hybrid system analysis confirms that the devices should cooperate well when the appropriate sizing and control strategy are applied. The use of conventional source is at the level of 20%, so 80% of running costs and emissions are to be avoided. (C) 2017 Elsevier Ltd. All rights reserved.