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.
Having now dealt with some of the methods adopted for passing warm air in large volumes into the rooms of buildings, as the sole means of warming and ventilation, I shall draw attention to a combined system, devised by Drs. Drys-dale and Hayward, in which use is made of warmed air in conjunction with open fires. This system is described in their work entitled Health and Comfort in House Building. It is an axiom that change of air in a room is essential tor health, and consequently that both an inlet and outlet for air must be provided; but no direct admission of cold external air into rooms should be tolerated. Moderately impure air. as pointed out by Dr. Inman, may not be so injurious as a draught of cold air. If the open fire is used, with a separate direct supply of fresh air from outside, this may, and in fact does, check the currents of cold air towards the fireplace, but rather diminishes the value of the ordinary chimney for ventilation. The fireplace should be studied with a view to economy of fuel, and not as a contrivance for the ventilation of rooms.
Drs. Drysdale and Hayward point out that no system of single-room ventilation and warming can be satisfactory, and that a general system is needed; they recommend the use of the kitchen fire as the means of causing the requisite suction, unless a special fire be set apart for the purpose. They also point out that the system of general diffusion of warmth throughout the house does not conduce to effeminate habits, or tend to induce a habit of avoiding exercise in the fresh air, but, on the contrary, is likely to diminish the tendency to bron-chitis and quinsy. Supposing, say the authors, that we have provided for the ingress of a sufficient supply of moderately-warmed fresh air for all the wants of the house, and for a sufficient suction to draw off the vitiated air, the next point is to see that this heat is not wasted, and unless special care be taken in the original plan of the house, this waste will occur. As soon as the front door is opened, the cold air from outside rushes in, and enters the hall, which, as a rule, passes between two seta of rooms direct to the main staircase, and the oold Mast rushes through the whole house, tending to reduce it to the temperature of the outer air; the usual plan of an inner door is not always effective, as the outer door is often left open. The hack door should open into the scullery or kitchen, or some other room where it is the interest of the servants to keep the door shut; the front door should open into a lobby or vestibule, to which the servants have separate access without going through the central hall of the house; and the windows, they say, should be made fast. The authors are no advocates of warming the house by heated air; all they recommend is the warming of the incoming air needed for ventilation, and this, unless the velocity is great, need not be heated above 65° F. for the comfortable supply of rooms otherwise wanned. It appears that Dr. Gordon Hogg had a house built at Chiswick, in which the authors' plans were carried out, except that no fires were used; within a year or two, however, fireplaces were added, and the windows made to open.1
Drs. Drysdale and Hayward consider that the best way of warming is by passing air over hot-water pipes, as this plan avoids burning the air. Two different houses are described. In house No. 1, there are no passages, and the incoming air is warmed by being passed over pipes heated by hot water at low pressure; in the case of the house No. 2, the same result is obtained by the use of small pipes with high-pressure hot water. The authors lay no stress upon the particular means adopted for warming the air, except that they consider that it should be done by surfaces at comparatively low temperature, and not by highly-heated surfaces as in a stove. The humidity of the air is a most important question, and it will not be satisfactory to merely heat the incoming air without paying any attention to its hygrometric condition. Air at 66o F. will hold about 6 grains of water suspended in each cubic foot, while air at 30° F. will only hold 2 grains of water in suspension. I have already pointed out the great objection to passing the air over highly-heated surfaces, as the contact burns and decomposes the particles of dust and organic matter, which are constantly present in the air, thus rendering it unpleasant for breathing.
The authors state that the primary inlet for the air-supply to the whole house should be in the basement, or perhaps it would be tatter to have such an inlet on each side of the building in order to be able to take advantage of the winds; or, to avoid dust and dirt, the inlet might consist of a flue carried up to a point above the roof, where it would be provided with an opening on each of four sides. The incoming air may be screened, washed, cooled, or perfumed according to taste, but it must always be borne in mind that the screening and cleaning operations afford great obstruction to the passage of the air, and it is doubtful, in my opinion, whether the suction of the kitchen-flue would have been so successfully used by the authors, if they had resorted to any of these method.
1 Drawings of this house appear in Plates XX. and XXI. and a drawing of a somewhat similar boose in Plate XXII. Further remarks on the system will be found at the end of Section XII. - ED.
They say the best place for the furnace of the warming apparatus is the basement of the stairs lobby, and proceed to describe the system as applied to the two houses before alluded to, the kitchen fire alone being used as a means for creating the necessary suction. House No. 2 had a central corridor upon each floor, and these were warmed in the following manner:- The warm air was first led into the ground-floor corridor, from which it passed up through a wide grating fixed in the middle of the ceiling; the air passed through between the ceiling and the floor above, and into the corridor above by a grating at each side running near the wall, as in Fig. 499, thence it passed similarly to the corridor above. These corridors thus became sources of warmed air, and the rooms on each side were fed from them by a series of holes, 7 inches long and 5 inches wide, formed in the cornice at the ceiling-level; the shape of the inlets is shown in section in Fig. 500, and as many were used as could be got in the length of the rooms. The vitiated air was taken off by similar orifices in the cornice at the opposite side of the room, and it was found desirable to avoid the resistance entailed by causing the current to pass at right angles to its previous direction; to obtain the desired result, the orifices were formed with an easy curve, as shown in Fig. 501, the form approximating as nearly as possible to the Schiele curve. The fireplace should if possible be at the side of the room opposite to the inlet of air, and, if convenient, the lower member of the cornice should be hollow for its entire length, and the opening into the room be protected with an ornamental grating.