A gas heater includes a support unit, a burner unit, a venting unit and a frame guider. The burner unit includes an ignition unit, a hollow and transparent radiant unit defining a cavity in which the flame guider is positioned, a heat reflector and a burner top cover. The radiant unit comprises a bottom unit with inlet air passages through which an air flow into the radiant unit cavity is created. Then, the frame guider, which has a preset structure such as a spiral and a cone structure and a plurality of guider through-holes, is arranged for guiding and generating a flame pattern which is visible through the radiant unit. The venting unit, which is connected to the radiant unit in an air-tight manner, then provides an air exit. Accordingly, energy utilization is increased and visible flame pattern assemble to real flame can be seen.