Abstract: Radiant tube space heating appliance (FIG. 1) has radiation ducting 10 with one or more inline burners 16 in a branch or branches 12 upstream of common tailpipe 20. An exhuast fan 22 in the tailpipe draws heated gases thought the ducting. A power operated control damper 28 in the tailpipe is actuated in response to sensing of the gas temperature in the tailpipe to reduce the induced flow therein when the temperature is below a certain level to counteract the increased volume throughput of the adjacent fan at lower temperature so that performance burners, e.g. on start up, is not adversely affected.