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.
Before describing the various systems by which the dwelling-house may be heated by hot or warmed air, it may be well to say that to use this as the Bole method of heating, to the exclusion of open fires, will not, in my opinion, commend itself to the average British householder. Rightlv or wrongly, we are so wedded to the system of open fires, that their cheerful appearance would be greatly missed, and would hardly be compensated by even an equable warmth all over any given apartment. It would, moreover, be very difficult, and in some cases practically impossible, to apply such a system to an old house, although it could easily be arranged for in the design of a new one. There can be no doubt that the mere cost of fuel burnt would be less, if a system of heating by hot or wanned air were applied, instead of the usual system of open fires, but the difference in the cost of fuel on the two systems would not be sufficient in most cases to turn the scale in favour of the hot-air system.
In many parts of the continent of Europe, and in the United States and Canada, the winters are very much more severe, and the variations of tempera-ture much greater, than in the British Isles, and in these cases it is found absolutely necessary to resort to means of heating more efficient than the ordinary open fire, and for this reason large close stoves, placed at some dis-tance from the walls of the rooms, are frequently used; hot-air warming. however, has found wide acceptance in North America, though more, I believe, for public buildings, such as schools, than for private residences.
Before describing the various methods of heating buildings by means of warmed air, it will be well to allude to some of the principal points which require attention: -
(a) Cleanliness of the air is essential, and therefore, if the external air be loaded with soot and dust, it most be passed through some filtering material before being delivered into the living-rooms.
(b) Freedom from disease-germs and noxious gases is also essential; it is therefore necessary to choose the position of the inlet with careful attention to the position of gullies, ventilators to drains, and apparatus of a similar nature.
Humidity of the air requires careful attention; the higher the tempera-ture of the air. the more water-vapour it will hold in suspension. It is therefore obvious that, if relatively cold external air be heated and passed direct from the ting-apparatus into the living-rooms, it will be in the best condition for taking up moisture, and. while eminently titled for use in the drying-closets of a laundry, it is very ill-adapted for breathing, and will necessarily cause the skin to feel parched, and the nose, mouth, and breathing-organs will be made dry and uncomfortable by the abstraction of their natural moisture. It is, therefore, very desirable that the air before delivery into the rooms should have imparted to it the proper humidity necessary to render it pleasant for breathing.
(d) The requisite volume of air must be passed in at such a velocity as to cause no perceptible draught, and it must then be extracted by a suitable flue of a height calculated to produce the requisite constant flow of air through the building.
(e) regulation of the temperature of the incoming air must be provided for by a system of simple valves.
The air must not be heated too much, otherwise the dust particles will be burnt, and a distinct and characteristic odour will be produced, which is wry unpleasant
In describing the Galton Stow and others of the same type, I have already stated that dust and other matters may be carried in with the incoming air. With a system in which the How of air through the heating-apparatus, and thence through the house, is solely induced by the heated column of air in a flu. it is usually found impossible to obtain sufficient suction to permit of the use of a filtering-apparatus, and therefore recourse has to be had to some means of inereasing the draught in the flue. cither by the use of a fire at the bottom of it. by the use of e radiator in a similar position, or by medianieal means, such as a rotary fan. In the Houses of Parliament, which are heated by carefully-homklrfted air. both fans and fires are used for causing the proper currents of air; but in the case of a house, it is desirable to avoid complication as much as possible, and I should deem the use of a rotary-fan to be undesirable except in a very large mansion.
If air be passed directly through the Hue-tubes of an apparatus in which the products of combust ion of the fuel play directly upon the tubes, there is always a risk that, by inattention on the part of the attendant, the surface of the tubes may become overheated; and than, instead of being warmed, the incoming: air will be burnt. The results obtained depend entirely upon the temperature of the heating-surface and upon the velocity of the air.
If the temperature in a living-room be examined at the floor-level, and at different heights above the floor, while artificial means of illumination are being used, it will be found that the air near the ceiling is extremely hot and much vitiated by the products of combustion of the gas, oil, or candles used for illumination, and also by the products of respiration. I am of course alluding to the usual arrangement where gas is burnt freely in the air, with no special flues for feeding the gas-jets with external air or getting rid of the products of combustion.
Figs. 484 to 488. - Various Arrangements for Entrance and Exit of Warmed Air.