A Physician’s Guide to Sanitation – Part 8

Cold-air box for furnace

For Parts 1-7, click here.


Every house, however small, should have an open fire for comfort and as an aid to ventilation, even though most of the heat flies up the chimney. Stoves save fuel, and will warm halls or connecting rooms or rooms on different floors by means of a “drum”; but they will not heat a whole house as well as a furnace. A “Galton” or “Jackson” ventilating grate is the best appliance for single rooms, serving at once as an open fire and as a closed stove. A furnace will warm several rooms as easily as one, and is more economical of fuel and less troublesome than several stoves. The important consideration is to secure a furnace that is large enough to serve without keeping a big fire, or heating the fire-pot red-hot, and thus “burning the air” as was formerly the rule in most dwellings. The fresh-air supply should never be shut off entirely even in zero weather. If the air seems dry, a wet towel should be hung in front of the register when the water will rapidly evaporate. Every room should have a chimney-flue; otherwise it will be as difficult to force hot air to enter it as it is to pour water into a bottle that is already full. So, also, warm air will rise to the upper floors, and not heat basement and halls. The heating-flues for lower floors should therefore connect direct with the furnace-dome, so that each can get its share of the heat. To warm an entrance hall is difficult on account of the upward “pull” of the staircase and the inrush of cold air. Storm-doors and a vestibule should therefore be provided, and the register should be placed under the stairs. Registers should be located on inner walls, and never on floors, as they collect dust, matches, etc., which may cause fires. If there is a ventilating skylight in the roof it will be easier to warm the house, as circulation of air is essential, and without such an arrangement the air will stagnate on upper floors. With an open fire one can sit in comfort with the thermometer at 50°F., whereas with stove or furnace heat 70°F will seem necessary.


The furnace should be located near the cold side of the house on account of the wind-pressure which makes it difficult to warm rooms facing northwest. The fresh-air supply should be taken from the same side, and the end of the box should be raised five feet above the yard level to avoid drawing in ground-air. If it opens under a veranda, the space around it should be kept free from leaves or other sources of impurity. The cold-air box should be tight, and should preferably be made of galvanized iron. It should have fine wire-netting at the end to keep out dust, and it should be cleaned every year. For large buildings a steam or hot-water apparatus is preferable to a hot-air furnace. It is claimed that the former is less troublesome, and that it warms every room regardless of exposure or how low the temperature. It costs more to install, but is more durable than a furnace. The objection to steam-heat is that it is difficult to regulate in mild weather while with the direct system the radiators are unsightly and warm the same air over and over again, and there is no ventilation. If the radiators have an air-supply from outdoors, they are liable to freeze in winter. The indirect system, by which fresh air is admitted to stem-coils in the cellar and then carried through flues to every part of the house, serves very well, though at greater expense. Hot water has the advantage of maintaining a more even temperature without overheating on mild days in spring or fall. The pipes are larger than steam-coils, and cost more to install, but the results are sanitary. The direct and indirect systems are often combined, and give entire satisfaction. The problem of warming is largely a matter of expense; but the saving in doctors’ bills and in increased mental and physical efficiency more than compensates for the outlay required to provide a really good heating apparatus.

Many persons imagine that the fire-box of a furnace connects with the hot-air flues, because smoke, coal-gas, and fine dust from ashes sometimes come through the registers. In reality, however, the smoke and dust escape into the cellar when the furnace doors are opened to put on fresh coal, are sucked through cracks in the cold-air box, and then drawn up through the registers. Few persons understand the mechanism of a furnace, because it is boxed in with brick or galvanized iron so that the interior parts are never exposed to view. Out of sight is out of mind. An ordinary furnace consists of a fire-pot of cast iron, lined with fire-brick, with a wrought-iron dome or cover set in a groove filled with sand so as to permit of alternate expansion and contraction of the metal when heated and cooled. This is enclosed in galvanized iron or brick, with small intervening space. Cold air is brought from outdoors through a box of wood or galvanized iron, and after being warmed by contact with the fire-pot is carried up through the flues constructed in the walls of the house. These flues open into living-rooms and halls through registers which can be closed by valves. To increase the efficiency of the furnace, various designs have been made to enlarge the heating-surface by the addition of flanges or vertical ribs with deep corrugations which are sometimes undulated, and into which the gases and smoke penetrate, thus increasing the heating surface very materially. Merely enlarging the space between the fire-pot and the outer casing would admit too large a volume of cold air in proportion to the heating-surface. Only the inner stratum of air would come in contact with the surface of the fire-pot, and the outer stratum would scarcely be warmed at all. The heavier the casting and the more numerous the convulutions, the greater the heat will be evolved. Another device which has proved successful has been the addition of an elaborate system of pipes – upright, horizontal, circular, conical, and cylindrical – which can be connected or disconnected at will, and which carry smoke and heated gases into the chimney. Most modern furnaces combine both features, being constructed with a fire-pot flanged and corrugated to increase the heating-surface, and having also a complication of smoke-flues so as to create direct and indirect drafts.

When the fire is started it connects directly with the chimney by a short cut, or direct-draft damper, as slightly warmed air can not be expected to be drawn through a round-about system of flues. After the chimney is warm enough to maintain a permanent draft, the direct-draft damper is closed, and the circuitous route through the system of pipes is utilized, bringing the entire heating-surface into action.

In addition to these provisions for controlling a furnace fire, sliding doors are provided in the upper and lower doors of the fire-pot. A check-draft damper is also placed in the main smoke-pipe or in the indirect-draft pipe to control the entrance of cold air. Various devices are employed to make this action automatic so that a furnace will become self-regulating. A furnace gives the best results and is most saving of fuel if the fire-pot in very cold weather is kept filled as high as possible, with the drafts regulated so as to keep a steady fire. A large heating-surface kept at a moderate temperature will prove far more effective than a smaller fire-box intensely heated by forced draft, which is wasteful of fuel and liable to crack the fire-pot.

To be continued….

  • From The Standard Family Physician: A Practical International Encyclopedia of Medicine and Hygiene Especially Prepared for the Household. Copyright 1907 by Funk & Wagnalls.

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