HEATING BY HOT WATER. 163 
Where several houses are built adjoining (side by side), 
and have to be heated from one boiler, or rather stoke-hole, 
the best plan is to run two mains, flow and return, trom 
the boiler across the ends of the houses, and by preference 
inside them, in a shallow brick pit or trench, so that 
there may be no loss of heat. On these mains T-pieces 
I a. 
Fic, 108. 
are fixed where required, that is opposite the flow and 
return (heating) pipes, on the two mains respectively, 
these being connected on and each fitted with a valve. Of 
course there will be a rise from the mains into the heating 
pipes, so that the former may run beneath the doorways 
or paths, etc., and this also ensures a proper circulation 
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