A compact gas-fired radiant space heater is adapted for residential use, having an output in the 20k BTU to 40k BTU/hr range and exterior dimensions small enough to allow it to be installed in a standard two foot by four foot suspended ceiling opening. A radiator tube having a total length of approximately 15 feet is bent into a serpentine shape, and combustion control components are housed within a plenum chamber supplying combustion air to the tube, both the tube and the chamber being encircled by a frame that fits within the two foot by four foot opening. The combustion control components are attached to a chassis plate whereby the components are removable from the plenum chamber as a unit to enhance serviceability of the heater. A burner venturi of novel configuration produces a flame that is less than four feet long yet which is relatively quiet. An air flow switch senses the dynamic pressure of an air stream issuing from a fan which pressurizes the plenum chamber, shutting off the supply of gas to the burner if the pressure reading indicates unacceptably low air flow.