We are in receipt of our annual crop of inquiries in regard to tte proper adjustment of hot-air furnaces, which we will attempt to answer as briefly, yet comprehensively as possible. The apparsAus for heating buildings with hot air may be divided into seren parts ; namely, the fire-box and flues in which combustidi performed ; the chamber through which the air passes to be heated ; the cold air pipes leading to this chamber ; the hot air pipes leading from it to the registers ; the registers which admit the air to or close it off from the apartments to be heated ; the external registers or openings which admit the cold air ; and, lastly, the registers by which the exhausted air is permitted to escape from the apartments to make way for the warmed fresh air which enters. We have here a complicated apparatus, each part of which is essential to the perfect working of the whole ; and the wrong adjustment of any may defeat the end sought ; namely, to heat and ventilate equally and perfectly all the apartments connected with the apparatus. The fire box should be cast very thick and heavy, the better to guard against sudden fluctuations of temperature caused by neglect in firing, or an overcharge of coal. The grate should be sufficiently open to admit of a good draft, and the ' dampers should fit accurately. In many cases the damper communicating directly with the smoke-pipe intended to be opened only in kindling the fire, becomes warped by the heat, so that it can only be imperfectly closed, and much of the heated gases passes through it instead of the heating fines, and thus escapes without having the heat abstracted. The grate should be easily dumped without danger of falling down, as is the case with many Hi-constructed furnaces, and the bottom dampers should fit as tightly as possible that the draft may be fully controlled. The outer side of the fire-box and fiues should be whitewashed. The chamber in which the air is heated should be of ample size in proportion to the capacity of the hot-air pipes which lead from it, and should always contain a vessel of water. The cold-air pipe leading to the heating chamber is in most cases too smalL We have often seen this pipe having a sectional area of only 72 square inches to supply a hot-air service, the aggregate sectional area of which was not less than 616 square inches ; making all due allowance for expansion, the cold air pipe ought to be twice as large in proportion as this. We have lately seen in an exchange a recommendation that the external openings of the cold-air pipes should be trumpet-mouthed. This was asserted to be a panacea against the effects of varying winds which often reverse currents of air and send the hot current out into the street instead of the parlor or library. We have tried this experiment and know that it will not do. The only thing that will do is a vaned hood, or cowl, which always presents its mouth to the current of wind, no matter from what quarter the wind is blowing. The hot-air pipes leading from the furnace are apt to get clogged where the registers open in the fioor, by servants sweeping all manner of rubbish into them, as dust, bits of rags, etc. This is not only an obstacle to the flow of air but renders the danger that your house may be burned somewhat imminent. Where, as is often the case, the hot-air registers open out at right angles from the side of a vertical pipe, one over the other, the top room will get the better of the others, unless the supply of hot air be far more than the capacity of the upper register to discharge. The branch register pipes should not join the main pipe at right angles, but at an acute angle, the apex of which is at the junction of the two pipes. Even then it may be necessary to extend a chute or apron from the upper side of the lower end of the branch pipe into the main pipe, so as to partially intercept the ascending current Finally, the ventilators should be in the bottom of the room. In this case the hot air which enters the room pure rises to the top, while the foul and effete air settles to the bottom.
This article was originally published with the title "The Adjustment of Hot-Air Furnaces" in Scientific American 21, 13, 201 (September 1869)