In heating a 10-ft. by 7-ft. span-roofed greenhouse, if an oil stove will not do, recourse must be had to a small boiler and hot-water pipes. Such an apparatus is made by nearly every boiler maker. It consists of a boiler just let into the wall of the house below the glass, the back of the boiler showing inside the house. The accompanying sketch shows such a boiler in section, and it will be seen that the flue pipe connection, and both feeding and stoking doors, are all outside the house, while the pipe connections are inside. The pipe connections and joints are simply made with rubber rings, and they terminate at the other extremity in a box-end, winch acts as a supply cistern, support for the pipes, and air vent.

Section of Greenhouse Boiler.