This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The subject of warming is one of the most important in the design of a dwelling-house, and the problem as to the best method to be employed in any particular instance, is not always easy of solution. Warming is so closely allied with ventilation that it will be impossible to avoid repeated mention of the latter subject, but fuller information thereon will be found in a subsequent section, written by another author.
So long as the temperature of the external air is above 60° Fahr., no system of warming will be found necessary in the British lsles, except in the cases of rooms or buildings occupied by invalids, where possibly a rise of a few degrees may be deemed desirable. When, however, the external temperature falls below 60° Fahr., some means of warming is desirable; and of course when the external temperature falls much below that point, it becomes essential to raise the temperature of the interior of the building, if the comfort of the inhabitants is to be obtained. Opinions vary in different countries as to the most desirable temperature for the interior of buildings; for instance, in the United States the internal temperature is often kept as high as 70° or even 75° F. Most Englishmen consider these temperatures too high for comfort, and it is generally agreed that a temperature of 60° F. is advisable in living-rooms, and about 55° F. in corridors. The temperature, however, should be kept constant, as directly fluctuations occur, there is a tendency to the production of draughts. In our climate, it is necessary to provide for raising the temperature of the interior of the building uniformly to 60° Fahr., when the external temperature is 25° Fahr. Even in the severest winter, the thermometer rarely falls below that degree of cold; and when it does, the apparatus, if properly designed, can be overworked to the small extent necessary.
Section X. - Warming By E. R. Dolby
Associate Member Or The Institution Of Civil Engineers. Member Of The Institution Of Mechanical Engineers, Whitworth Scholar
The methods adopted and considered desirable in different countries vary so greatly, both from the great differences in the range of temperature and from the prejudices of the various peoples, that I have thought it best to consider the question of warming in its restricted application to dwelling-houses in the United Kingdom, and in countries having approximately the same climatic conditions. Again, the dwelling-house may be considered under two different aspects: firstly, the ideal house which one would desire to have built and to occupy personally; and secondly, the house provided by the speculative builder. and bought, leased, or hind by the tenant. At the first glance, there may seem to be little difference between the two classes of houses so far as wanning is concerned, but there is this essential distinction: if a house be specially designed by a capable architect, for a client who requires the building to be provided with a suitable system of warming and ventilation, - for the two points must be considered at the same time, - then the design may be arranged so as to obtain the most efficient system, so far as that particular house and local circumstances are concerned. Whereas in the other case, the system which can be applied is at a makeshift and an addition, for it can rarely be said that the problem of wanning receives very special attention from the speculative builder.
The systems in use may be divided into two groups: firstly, those in which the warming is produced from a number of separate and distinct heating-centre-, such. for instance, as open tires; and secondly, systems in which the whole of the house is, or may bc, wanned from a central source, which distributes the warmth over the building. I shall endeavour to point out the special advantages and disadvantages of the two systems, although in many cases it will be found desirable to use both systems jointly in the same building.
The chief requirements of a good system of warming are the following: -
(a) The apparatus should produce and keep up an equable warmth all over the building, or, at least, an equable warmth over every part of a given apartment.
(b) The apparatus should not vitiate the air in any way; that is to say, it should not give off objectionable fumes, smell, or gases, which can enter the apartment.
(c) The apparatus should not lessen the humidity of the air; that is to say, the humidity of the internal air should be such as would be found in external air, at the temperature of 60° F., on a still morning in spring.
(d) The apparatus should not require skilled attention, or be likely to explode, or to cause damage to property, even if somewhat carelessly handled.
(e) The apparatus should be of such a nature as to tend to promote ventilation, and in doing so should not impair the incoming air for breathing purposes.
In discussing the advantages and disadvantages of the various systems, the value of each will be assessed by the way in which it fulfill the above requirements.
In some kinds of warming-apparatus, provision is made for allowing the external air to enter through the apparatus, so that they provide ample ventilation and also warmth at the same time. In view of this, it may be desirable to glance at the experimental data which have been obtained. Some persons are much more sensitive to draughts than others, but the conclusions deduced by Sir Douglas Galton and others, from experiments, may be accepted, namely, that a current of air having a velocity of 3 feet per second causes no inconvenience, while a current with a velocity of 5 feet per second is objectionable, and one with a velocity of 10 feet per second is felt as a strong draught. A good deal of discussion has taken place from time to time as to the number of times per hour that the air in a room should be changed, and opinions have differed greatly. It is usually conceded that from 1500 to 1800 cubic feet of fresh air should be provided per hour per person, in order that the ventilation may be perfect; if the lower figure be taken, and a velocity of 3 feet per second be allowed to the incoming air, it is obvious that the area of the inlet must not be less than about 20 square inches per person. If this orifice be arranged so that the in-coming air passes over or through the heating-apparatus, then the surface of the latter must be so calculated as to enable it to warm the volume of air to the required temperature.