This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The directions given for the care of steam heating boilers apply in a general way to hot water heaters as to the methods of caring for the fires and for cleaning and filling the heater. Only the special points of difference need be considered. Before building the fire all the pipes and radiators must be full of water and the expansion tank should be partially filled as indicated by the gage glass. Should the water in any of the radiators fail to circulate, see that the valves are wide open and that the radiator is free from air. Water must always be added at the expansion tank when for any reason it is drawn from the system.
The required temperature of the water will depend upon the outside conditions and only enough fire should be carried to keep the rooms comfortably warm. Thermometers should be placed in the flow and return pipes near the heater as a guide. Special forms are made for this purpose in which the bulb is immersed in a bath of oil or mercury. See Fig. 52.