STEAM VS. HOT WATER. 43 
3. The heat from steam distributes itself over a great 
length of pipe more readily than that from hot water, and 
steam, therefore has a distinct advantage for heating long 
runs. 
4. Steam is preferable to hot water for irregular and 
crooked circuits. 
5. Unfavorable conditions of piping can be more readily 
overcome with steam than with water. 
6. The addition of crooks and angles in pipes is deci- 
dedly disadvantageous to the circulation of hot water, 
and of steam without pressure; but the effect is scarcely 
perceptible with steam under low pressure. 
7. In starting a new fire with cold water, circulation be- 
gins with hot water sooner than with steam, but, in ordina- 
rily long runs, it requires a longer time for the water to 
reach a point where the temperature of the house is ma- 
terially affected than for the steam to do so. 
8. The length of pipe to be traversed is a much more 
important consideration with water than with steam, for 
the friction of the water upon the pipe is much greater than 
the friction of steam, and a long run warms slowly with 
water. 
g. It is necessary to exercise greater care in grading pipes 
for water heating than for steam heating. With steam, a 
satisfactory fall towards the boiler is much more important 
than the exact manner of laying the pipes. 
10. In heating by water in closed circuits, a high expan- 
sion tank may increase the efficiency by allowing the water 
to become hotter throughout the system, and probably by 
giving a better circulation. 
Piping. —The arrangement of the pipes must be adjusted 
by the shape and size of the house and the crop to be 
grown. The ‘‘cool’’ plants, like lettuce and cauliflower 
(see page 5), do best without bottom heat, and for these 
crops the pipes should be above the soil or bed. The 
““warm’’ plants, like tomato, melon and cucumber, require 
bottom heat, and for these the return pipes, or some of 
