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In Japan, electric heat pump water heaters (‘Eco Cute’) that use CO2 as the refrigerant is spreading rapidly, which has been a big threat to gas companies in Japan and similar threats could be imposed on European gas companies. To improve the heat efficiency of gas water heaters, we studied a hybrid type water heater that combines a conventional gas water heater and a heat driven heat pump cycle. With a target heat efficiency of approximately 120%--a dramatic increase over the 90% efficiency of a conventional gas water heater--this hybrid gas water heater (here after known as HGWH) is expected to be an energy-saving replacement for household or commercial users and could be a countermeasure against the Eco Cute. The HGWH combines a single-stage adsorption heat pump cycle and a conventional gas water heater, which are operated either simultaneously or independently depending on the outside temperature, making year-round high heat efficiency operation. We evaluated the feasibility of HGWH using a prototype we constructed. We found that a compact system can be achieved, and heat efficiency of this HGWH achieves 110% to 120%, which is comparable with heat efficiency of Eco Cute.