The Garden Under Glass

CHAPTER XXVI HEATING AND STOKING To be really useful, a greenhouse must by some means be heated. It is possible to grow plants in an unheated struc-ture, but the winter is a very trying time, not only on account of the difficulty of keeping out frost, but owing also to the great amount of moisture which will accumu-late and cause damping off of flowers and foliage. To prevent worry the greenhouse should be heated, even if the fire is only kept in during the severe weather. The First Principles of Heating Whoever wishes thoroughly to understand how to keep a greenhouse fire so alight that while there is always sufficient heat there will never be too much, and there will never be any serious fluctuations of temperature, must set himself to understand the principles of heating. But as space does not here admit of an exhaustive treatise on the subject, I will confine myself to an explanation of how the heat may be steadily maintained. It will be presumed that a good boiler has been chosen well above its Work, that the pipes in sufficient quantity have been fitted, that the valves and air taps work freely, that the flues are clear, that the boiler and pipes are filled with water, and that everything is in readiness for the fire to be kindled. The aim is, by keeping a good fire, to heat the water. Ihe backbone principle of the heating is that hot water rises 256