159. Equivalents of Electrical and Heat Energy.. 160. Expense of Heating by Electricity... 174. Specifications for Plain Tabular and Water-tube Boilers.. 175. Protection from Fire-Hot Air and Steam Heating.. A TREATISE ON HEATING AND VENTILATING BUILDINGS. CHAPTER I. INTRODUCTION. NATURE AND PROPERTIES OF HEAT. 1. Demand for Artificial Heat.-The necessity for artifi cial heat depends to a great extent upon the climate, but to a certain extent on the customs or habits of the people. In all the colder regions of the earth artificial heat is necessary for the preservation of life, yet there will be found a great difference in the temperature required by people of different nations or races living under the same circumstances. On the continent of Europe, 15 degrees centigrade, corresponding to about 59 degrees F., is considered a comfortable temperature; in America it is the general practice and custom to maintain a temperature of 70 degrees in dwellings, offices, stores, and most workshops, and a heating apparatus is considered inadequate which will not maintain this temperature under all conditions of weather. 2. Magnitude of the Industry of Manufacturing and Installing Heating Apparatus.-The industry connected with the manufacture and installation of the various systems for warming is a great one and gives employment to many thousand workmen. The manufacture of heating apparatus is not only of great magnitude, but it is varied in its nature; all kinds of apparatus for heating-as, for instance, the open fireplace built at the base of a brick chimney, the cast-iron stove with its unsightly piping, the furnace and appliances for warming air, apparatus for heating by steam and also by hot water-can be readily bought on the market in almost every form, from that of the simplest to that of the most complicated design. The exact amount of capital invested in this industry could. not be ascertained by the author, but in twenty cities, selected in alphabetical order from a list of one hundred and sixty-five cities of the United States containing over twenty thousand inhabitants, the total amount invested in the business of erecting and installing heating apparatus as given in the Census Report by the U. S. Government for 1890 was $12,910,250, and the yearly receipts for 1890 from this business in the same cities was $5,592,148. The aggregate population of these cities was 1,573,508 people. This would indicate an investment of $8.20 and a yearly expenditure of $3.52 for each inhabitant. Reckoning on the same basis for the cities of the United States which contain over 25,000 inhabitants each, we should have an invested capital of over $106,000,000 and a yearly expenditure of over $46,000,000. These numbers are probably less than the amount actually invested, but they serve to give an idea of the magnitude of the industry connected with the supply of apparatus for artificial warming. 3. Nature of Heat.-Before consideration of the methods of utilizing heat in warming buildings a short discussion of the nature and scientific properties of heat seems necessary. Heat is recognized by a bodily sensation, that of feeling, by means of which we are able to determine roughly by comparison that one body is warmer or colder than another. From a scientific standpoint heat is a peculiar form of energy, similar in many respects to electricity or light, and is capable, under favorable conditions, of being reduced into either of the above or into mechanical work. We shall have little to do with the theoretical discussion of its nature, but, as it is well to have a distinct understanding of its various forms and equivalents, we will consider briefly some of its important properties. Heat was at one time considered a material substance which might enter into or depart from a body by some kind of conduction, and the terms which are in use to-day were largely founded on that early idea of its material existence. The theory that heat is a form of energy and is capable of |