HEATING BY HOT WATER. 205 
employed, the first 5ft. or 6ft. from the furnace must 
be built of brick, as the pipes are apt to crack badly 
under anything like a strong heat. In the case of a 
single flue, a good sized soot-door should always be 
built into the base of the chimney, both to enable it to 
be cleaned when necessary, and also to allow of an armful 
of shavings or straw being burnt, in order to create a 
draught when the flue is damp and cold, or the wind 
contrary. The worst of these single flues is that if the 
YZ 
Vas Mle, 
Fig. 142. 
chimney grows cold, or the wind is wrong, it may stop 
drawing, and then the fumes, which are very destructive, 
are discharged into the interior of the structure. 
The double flue previously recommended, and which 
is illustrated in Fig. 142, is immensely superior to all 
others in that the chimney is easily warmed at any time, 
or the fire in the furnace drawn up bright in a few minutes, 
by simply pulling out a damper, while the chimney itself, 
being built close to the furnace, is far more likely to 
