186 GREENHOUSE CONSTRUCTION AND HEATING. 
piping. It is not a quick heating boiler, but when once’ 
the water becomes hot it will remain so for a considerable 
time, even after the fire goes out. This boiler, which is on 
the whole more suitable for heating public buildings, 
large churches, etc., than horticultural structures, is 
sometimes made with a water-way end, and also with 
cross-tubes, which greatly increase the heating power. 
The comparatively new class of horizontal tubular boilers 
FIG. 127. 
have, however, to a great extent displaced this and other 
allied types, by reason of their greater power and com- 
paratively small cost. 
These horizontal tubular boilers are now frequently 
preferred by many market growers and nurserymen, and 
where long ranges of piping have to be heated they are 
probably at once the best and cheapest description of boiler 
