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.
It has been my endeavour, in the foregoing remarks upon ventilation, to lead those who have to build and those who occupy houses, to realize the intricacies of the subject when regarded as affecting communities as well as individuals; that it is, in fact, the maintenance of the outer atmosphere in a state of purity.
1 For farther information on Combined Warming and Ventilating Systems see pp. 93-108, and 225-228, Vol. II, and Plata. XX, XXL. XXIL, and XXIII. - ED.
without which pure air cannot be expected within houses; that contamination of Otherwise pare air will take place in and about dwellings, unless constant cleanliness throughout is exercised; and that the situation and arrangement of houses, the materials of which they are built, the manner of their construction. and also of their fitting-up and furnishing, will exercise consiiderable influence upon their ventilation.
It has also been pointed out that, apart from definite air inlets provided for ventilation, air may, and in almost every case will (particularly when open fires are in use), be drawn from sources frequently difficult to trace, and that such sources may be contaminated; and that, with the best possible arrangements provided for securing adequate change of air. efficient ventilation can only be secured by the constant attention and watchfulness of those who occupy the buildings, or of those entrusted with the care thereof, principally for the reason that change of air within a building is most frequently brought about by move ments of the outer air, which constantly vary, and because comfortable change of air within is greatly affected by the temperature of that without, which also is subject to considerable variation.
Only by propelling air by mechanical means into a building is it possible to ascertain the source of the air-supply, to be able to cleanse it. temper it. and to regulate its hygrostatie condition, as well as cause it to circulate throughout the several apartments of a building without causing currents or draughts which may be unpleasant to occupants.
"The Theory and Practice of Ventilation", published in 1844 by David Boswcll Reid, M.D., F.R.S.E., is replete with interesting facts and information. but partly, I am inclined to think, because he had not the appliances to work with which now are attainable, and partly because in some cases bis observations have led him to wrong conclusions, his deduction are not to be fully relied on. This is most unfortunate, because 1 find so many recent writers on ventilation appear to take them all for gospel, and continue to disseminate views which now cannot be supported by facts,
The general condemnation of downward ventilation is a case in point; it has been called down-draught ventilation, and consequently condemned, for a down-draught is generally recognized to be objectionable, but it is now abundantly proved that, with air gently travelling in a downward direction, it can be supplied pure and with comfort even to each separate individual in a crowded hall; and, as previously explained, change of air in an ordinary apartment where there is an open fire, principally takes place in a downward direction.
The placing of inlets and outlets on opposite sides of a room is another of those errors, in past times originated, still handed down and followed by the unthinking. Windows are not intended to be included in this condemnation; as already explained, they may with advantage be on different sides of a room, as they can then be employed for quickly securing, at suitable times, a thorough ehange of air in the apartment.
In conclusion, let it be remembered that in ordinary dwelling-houses, what-ever ventilating appliances may be considered advisable, it is essential that they be simple in construction, and easily regulated, and that anything in the form of ducts or Hues must be of sufficient area to permit of ready access for cleansing, and must be periodically cleaned; and. as it is only by the employment of mechanical means that the flow of air in any one direction can be continuously regulated, and as such mechanical means cannot be economically employed in separate dwellings, there is at all times a liability from the varying temperature of the inner and outer air, or from the direction or force of the wind outside, to a reversal of currents, so that the inlets may become outlets and the outlets inlets; consequently, unless the outlet- as well as the inlets are maintained in a clean condition, the air admitted may in its passage through them become contaminated, and so prevent the possibility of securing efficient ventilation.