Book - School of Science and Technology

106 Survey of heating methodsReturn airductFilterFlueFanHeatexchangerDraughtdiverterBurnerPlenumboxOutletgrillesFigure 4.9 Gas-fired domestic warm air unitWhile it is generally to be preferred that such equipment should be provided with aconnection such that flue gases are discharged to the outside air, the advent of natural gasand the increasing use of bottled gas have led to the development of `direct fired' airheaters, as shown in Figure 4.10.Directionalair outletsLine typeburnerAir supplyfrom outsideFansFigure 4.10 Gas-fired industrial warm air unit (Wanson)