50 



FAKM BUILDINGS IN SOUTH AFEICA 



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either through, or at least very near to, the fire. The reason for this 

 is that the draught is due to hot air, which ascends the flue on account 

 of its being lighter than cold air. Thus a high opening above the fire 

 is bad, because it allows an excess of cold air into the flue and, in this 

 way, spoils the draught. The arch bridging the fire-place should therefore 

 be situated not far above the grate. 



This arch should be built upon, and strengthened by, a turning bar 

 (or bars) as already mentioned in the section devoted to arches (page 44). 



Flues (see Figs. 46, 47, 214, and 214b). — Each fire-place should have a 

 distinct and separate flue to itself. If the flues of two different fire-places 



communicate, then when one fire 

 only is lit, air coming from the 

 flue of the other will interfere 

 with the draught. Further, smoke 

 from the active flue may find its 

 way down the other flue, and 

 enter the apartment from which 

 the latter leads, causing what is 

 known as " back smoke." If the 

 partition or withe, between two 

 adjacent flues be badly built, 

 communication between them 

 may be established, thus giving 

 rise to the above evils. 

 Flues should not be built bigger than the size necessary to carry 

 off the smoke. If a flue be made too big the draught is unsatisfactory, 

 and it is easier for gusts of cold air to stream down the flue, so causing 

 the fire to smoke. Generally speaking a flue 7 or 8 inches square is 

 sufficient to carry off the smoke from small grates or stoves, while a 

 flue 9 or 10 inches square will do for large kitchen ranges. The ordinary 

 flue in single-storey cottages is made 7 or 8 inches square. 



It is advisable to build flues with a curve in them, to prevent rain 

 from beating down on to the fire, and also to stop down-draughts of 

 cold air. The deflection of the flue, due to this curve, should be great 

 enough to prevent a person, looking up the flue, from seeing day-light. 

 The curve should be gradual; no flue should contain sharp turns or 

 angles, because these would interfere with the draught. 



Immediately above the fire-place the brickwork is gathered over, 



Fig. 46. 



Fig. 47. 



