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 ventilation of rooms in ordinary dwelling-houses is usually sufficiently provided for by the door, windows, and fireplace. Efficient ventilation consists in providing both inlets and outlets for air, and includes the complete control of both.
For admitting the outer air, no better means exist than that obtained by slightly lowering the top sash of a window; this, if opened only an inch clear of the upper bead, will expose a total space at that part - in a three-feet wide window - of 36 square inches, and an equal amount at the meeting rails. Here. we have a perfect ventilator possessing both inlet and outlet openings. The inlet at the meeting rails just above one's head, and with an upward inebriation; the outlet near the ceiling, to which the heated air ascends.1 This method, however, seems to be too simple and commonplace for the novelty-loviug popular mind, which is more satisfied with some jimcrack invention. A less satisfactory method consists in providing a loose piece of wood to be put under the lower sash; this gives one opening only in the window, and that at the meeting rails. A better arrangement is to make the lower sash with a deeper bottom rail, and to increase the height of the lowest bead of the hash-frame to correspond; the lower sash can be raised (say) 2 in. so as to admit air at the meeting rails without allowing any to enter at the bottom of the window.
It is claimed as one advantage derived from open fireplaces, that when in use they aid ventilation. Of course this is true, but the floor-level is not the proper position for an extract-ventilator, unless warm air is supplied from a higher point How often, in small rooms especially, do we find intolerable draughts of cold air rushing across the floor from door to fire, which no amount of "listing" or curtain arrangement will adequately prevent This is unscientific ventilation, almost useless (being confined to a part where it is least required), and likely to be injurious to health. The best way to extract overheated air from a room is through a special air-flue, formed in the chimney-breast at the side of the smoke-flue, opening into the room near the ceiling through an ornamental grating, and at its upper end into the roof-space above the topmost ceiling. This, however, can only be arranged for daring the construction of the house. In houses already built, a flap-valve, opening only inwards, can be fixed in the chimney-breasl as to admit the vitiated air into the smoke-flue. This will not only allow foul air to escape, but, by partially satisfying the voracious chimney, will lessen the intake at the floor-level, and consequently the before-named objectionable draughts. Against the use of this valve are the inevitable discoloration of the wall-paper near it, and the clicking sound of its flaps.
Another method of decreasing the violent extraction of air from the lower part of the room, which is capable of application after the house is built. to supply the fire and chimney with air from outside the house; or. in a lower room, from beneath the ground-floor. This can be accomplished by fixing a tube at the side of the chimney-breast, opening into the chimney both above and below the fire, as shown in Fig. 675. This tube, fitted with valves, gives much control over the air-currents: with both valves closed the chimney will draw air only from the room; with the lower one only open, the room-draught will be lessened, and the tire burn as rapidly as before; and, with the upper one only open, the room-draught will be eased, and consumption of fuel economized. Other possible modifications will also be apparent to the reader, such as opening both, or partially opening one or other of the valves. With the ground-floor arrangement an additional advantage is gained by increasing the ventilation under the floor.
1 When a fire is burning in the room, both openings will usually admit air; this also will frequently be the case even without ft fire in the room. - Ed.
Where none of these things can be done, and it is desired to decrease the discomfort caused by draughts across the floor of the room, it is better freely to admit the air near the top of the wall next the outer passage, than to try to stop its entry by packing the door. It will then be warmed by passing through the upper air on its course to the fire, thus diffusing the heat through the room, and at the same time diluting and assisting to remove that portion of the air which is the most impure.
In sleeping-rooms, where fires are seldom lighted, the air during occupation is quitter than that in living-rooms, the door and windows being generally closed. Here floor-draught is good, as the carbonic acid exhaled by the sleeper is, under these supposed conditions, likely to fall to the lower part of the room, and may thus be removed. The air-current is of course not so violent when there is no fire, and therefore little or no inconvenience is felt as it passes to the chimney from under the door. The chances, however, are often against the air taking this direction, as many people never have a fire in the bedroom, in which case the flues become cold, and in the winter, damp; under these conditions an upward air-current in them is not to be relied upon. An occasional fire in the bedroom grate during the winter for the purpose of warming the flues, is very helpful in maintaining healthful conditions of gentle ventilation. In the summer the upper window-sash ought rarely if ever to be quite closed, perhaps only in damp or boisterous weather.
Small rooms in which there are no fireplaces are sometimes found, and where the window and door are at the same end. These are not suitable for bedrooms, as the ventilation of the back portion can never be efficient. It can, however, be improved if the floor-joists run from front to back, by using the space between two of them as an air-tube, with a grating in the outer wall at one end, rod a Tobin tube at the inner end, as shown in Fig. 676. If this car be done under the floor, it may be accomplished above the ceiling, between the plaster and the upper floor-boards, or an air-duct may be constructed under the celing in the room itself; in these cases
Fig. 675. - Elevation of Draught-regulator for Fireplace.