Fireplaces and flues
There are a number of ways of arranging fireplace recesses and chimney breasts. Typical examples are shown in Figs 19 and 20, which also indicate the bonding of adjacent courses. If a fireplace is on an external wall, the thickness of the back of the recess “T” may be a minimum of 100mm (4in.) as shown, provided that no combustible cladding is carried across the back of the recess. However, this means that there is little insulation between the back of the fireplace and the outside air, and this tends to give a cold flue which may adversely affect the heating appliance. It is preferable to provide increased insulation by carrying the cavity across the back of the fireplace as shown in Fig. 20.
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