HEATING BY HOT WATER. 157 
(Fig. 101), and the ordinary flow and return, with single 
pipes (Fig. 102). In both of these systems the water is 
certain to circulate properly, provided that the levels are 
correct and the pipes 
kept full of water. & 
The first method is 
frequently employed _ 
for heating span- 
Fig. 101. 
roofed houses of 
small to moderate size, from which frost only has to be 
excluded, when a single ring of 3in. or 4in. piping will 
suffice. In such a case the best place for the boiler (a) 
is at the end where the door is, between it and the corner 
of the house, as shown, so that the connection may be fixed 
directly from the boiler into the flow pipes. The row of 
pipes is taken right round the structure, close to the eaves 
or wall-plate, and the return is led down beneath the 
pathway, close to the door, and into the boiler again at 
the bottom. 
The other method (Fig. 102), is more suitable for a narrow 
lean-to or three-quarter span structure, where a couple of 
rows of 3in. or 4in. pipes fixed along the front of the house, 
either above the bed 
or stage, or below 
the latter, will afford 
sufficient heat for 
many purposes. If 
a rather higher 
temperature is required, ¢hree rows of piping may be 
employed instead of two only (see Fig. 103), and in this 
case there should be one flow and two returns, as shown, 
Fig. 102. 
