The purpose of this study is to modify the kerosene furnace, which is forced flue type with 15000kcal capacity, to gas furnace satisfying for CITY gas, LNG gas and LPG gas. The gas furnace, a kind of gas appliance, is mainly used for heating houses by combusion of gas. This paper describes briefly the design technology for gas burner which is most important in replacing kerosene fuel with gas fuel. Especially, the design for gas nozzle is constructed by theoretical and experimental method. It is found that the experimental results of the modified gas burner are good agreement with the theoretical results for calorific value and combustion efficiency. The result of this study will contribute in the design skill and of gas burner and similar gas appliance, and the pursuit for reduction of fuel cost as well as atmospheric pollution.