■ w 
 
 tpZ% 
 
 PRACTICAL SUGGESTIONS RESPECTING 
 
 THE VENTILATION OF BUILDINGS. 
 
 A REPORT TO THE STATE BOARD OF HEALTH. 
 
 BY JOHN H. KELLOGG, M. D., MEMBER OF THE MICHIGAN STATE BOARD OF 
 
 HEALTH, BATTLE CREEK. 
 
 [Reprinted from the Nineteenth Annual Report of the Michigan State Board of Health, for the fiscal 
 
 year ending June 30, 1891 ] 
 
 [Reprint No. 395.1 
 
PRACTICAL SUGGESTIONS RESPECTING THE VENTILATION 
 
 OF BUILDINGS. 
 
 A REPORT TO THE STATE BOARD OF HEALTH. BY JOHN H. KELLOGG, M. D., 
 
 MEMBER OF THE BOARD. 
 
 Gentlemen: —In obedience to your request, I herewith present in brief 
 form a few suggestions and fundamental principles which it is believed 
 may be found of service in arranging the ventilating system of public and 
 private buildings. The sole effort has been to embody, in as brief 
 and lucid a form as possible, the information which the writer has 
 gathered during some years of study of the subject, and such facts as he 
 has gleaned from his own experience in planning and superintending 
 buildings of some size for hospitals and other purposes. The only rec¬ 
 ommendation offered for the plans and principles suggested is that they 
 have borne the test of practical experiment in a satisfactory manner, 
 which cannot be said respecting all the schemes for the warming and ven¬ 
 tilation of buildings which have been offered in works on sanitary sub¬ 
 jects published within the last score of years. In justice to himself, the 
 writer ought to say that he has not undertaken to make this paper exhaust¬ 
 ive, or anything more than what its title indicates; neither has he under¬ 
 taken to enter the field which properly belongs to the architect, but rather 
 to present simply such suggestions and theories as he has himself found 
 of practical value, and which are susceptible of general application, 
 omitting altogether the minor details, which, however necessary to the 
 adaptation of a general plan or principles to any particular case, are likely 
 to be of little service except in the special conditions to which they are 
 specially adapted. Seeking, then, to avoid as much as possible redundancy 
 of language and circumlocution in methods of presentation, let us begin 
 at once the discussion of the things most essential in a correct scheme for 
 the proper ventilation and heating of a building. 
 
 First of all, it may be stated that the ventilation and heating of a build¬ 
 ing must be considered together, for a successful working of each will 
 depend upon the conditions of the other. It needs no argument to 
 impress the fact that the amount of heat to be furnished in any given 
 instance must depend very largely upon the amount of fresh air to be 
 supplied per hour or minute. If the air of a room is to be changed four 
 times per hour, certainly a proportionately larger quantity of fuel must 
 be consumed than if the air is to be changed but once an hour. 
 
 The air supply of a room or building is generally determined by its 
 size rather than by the number of persons by which it is to be occupied. 
 This is certainly not a scientific method. A large room, occupied by but 
 one or two persons might possibly admit through cracks, about windows and 
 doors, and through its porous walls a sufficient air supply; while a small 
 room, crowded with people, would require a very large provision for the 
 supplW of fresh air. The first thing, then, to be considered in the study 
 of the ventilation of a room or building is the number of persons who are 
 [to occupy the space under consideration. 
 
 According to the most eminent sanitary authorities of England, each 
 
SUGGESTIONS RESPECTING VENTILATION OP BUILDINGS, cxix 
 
 healthy adult person requires not less than three thousand cubic feet of 
 air per hour. This statement is based upon careful experiments, which 
 showed that if the normal quantity of carbon di-oxide contained in the 
 atmosphere, which is two parts to every five-thousand parts of air, is 
 increased to three parts in five thousand of air, the limit of tolerable 
 impurity is reached; that is, if the amount of C0 2 is increased by respira¬ 
 tion to a larger proportion than that stated, namely, three parts in five 
 thousand, the air thus contaminated becomes productive of disease. It 
 must not be supposed that the poisonous properties of such air are due 
 to the chemical compound C0 2 . Air may contain a much larger propor¬ 
 tion of C0 2 provided this compound is derived from purely chemical 
 sources, without injury being apparent. But when the C0 2 is furnished 
 by the respiration of animals, there is associated with it a subtle poison, 
 which has been shown by the eminent physiologist, Prof. Brown-Sequard, 
 to be one of the most powerful poisons known, exceedingly minute quan¬ 
 tities being sufficient to produce death. 
 
 A little computation based upon the experiments referred to will show 
 that Dr. Parke’s figures are certainly not extravagant. With each breath, 
 each human being exhales into the air one cubic inch of carbon di-oxide, 
 and a definite amount of organic poison associated with it. As air 
 naturally contains two cubic inches of carbon di-oxide in every five thous¬ 
 and cubic inches of air, and as an additional cubic inch of C0 2 , or three 
 cubic inches in five thousand cubic inches of air is the limit of safety, it 
 is evident that each breath renders unfit for further use, five thousand 
 cubic inches, or approximately, three cubic feet of air. The average per¬ 
 son breathes eighteen times per minute; consequently, each person spoils 
 or renders unfit for further use, 3x 18, or 54 cubic feet of air per minute. 
 54 X 60 gives us, as the amount of air which each person contaminates per 
 hour, 3,240 cubic feet, a slight excess over the amount named by Prof. Parkes. 
 Some other authorities place the line of dangerous contamination at a 
 somewhat higher point, and consequently they require a smaller amount 
 of air. Avoiding either extreme, we may place the amount of air required 
 per hour for each healthy person, at about 2,400 cubic feet. It must be 
 understood, however, that this rule applies to healthy persons only, and 
 is not applicable to hospitals or buildings occupied by infirm or sick per¬ 
 sons. For such institutions, and for manufacturing establishments in 
 which the air may be contaminated by chemical or other processes, at least 
 double the amount named, or 5,000 cubic feet of air per hour must 
 be supplied. In any given case then, to ascertain the amount of air 
 required per hour, we have only to multiply 2,400 or 5,000 as the case may 
 be, by the number of persons to be supplied with air. The number of 
 persons taken should be the maximum rather than the minimum number 
 which the room or building is calculated to accommodate, for the evident 
 reason that the capacity of a ventilating shaft, duct or opening, may be 
 easily diminished, but cannot be so readily increased. 
 
 Having determined the amount of air required in any given case, the 
 following important practical points remain to be determined: 
 
 1. The circulation of the fresh air. 
 
 2. The area of fresh-air inlets. 
 
 3. The area of foul-air outlets. 
 
 4. The location of foul-air outlets. 
 
 5. The construction and location of foul-air ducts. 
 
 6. The location, sectional area and height of ventilating shafts. 
 
cxx STATE BOARD OF HEALTH.—REPORT OF SECRETARY, 1891. 
 
 7. The question of artificially assisting the draft by means of a pressure 
 or suction fan, or by means of heat in the ventilating shaft. 
 
 We will consider each of these several questions in the order named. 
 
 1. A room cannot be properly ventilated without an efficient arrange¬ 
 ment for the circulation of air. For this there must be for each space to 
 be ventilated at least two openings: one for the admission of fresh air, the 
 other for the removal of impure air. Nothing could be more absurd than 
 the frequently witnessed attempt to ventilate a room by supplying it with 
 a ventilating shaft connected with proper ducts and foul-air openings, but 
 without any provision for a supply of fresh air. Such an arrangement is 
 eminently well calculated to produce dangerous drafts through the open¬ 
 ing of windows, and the impression that any attempt at efficient ventilation 
 is liable to result in failure. It is also essential for the proper distribution 
 of the air admitted to a room that the air shall be heated before it enters 
 the room or building, or at the moment of entering. 
 
 2. To determine the required area of fresh air inlets, the amount of air 
 required and the velocity at which the air is to travel must be known. Air 
 heated to a temperature of 40° F. above that of the external air will travel 
 at the rate of about five feet a second when entering a room of ordinary 
 height, from which it may escape readily. If the escape of air from the 
 room is assisted by means of an efficient ventilating shaft the velocity of 
 the incoming air may be safely computed as ten feet per second. If the 
 fresh air enters the room at a temperature so high as 120° F. to 150° F. 
 the velocity of the air-current will be increased to 12 or 15 feet per second. 
 Better practical results are obtained by large volumes of moderately 
 heated air, traveling at a moderate speed, than from super-heated air 
 traveling at a high velocity. 
 
 Calculating the velocity of the incoming air at ten feet per second it is 
 only necessary to divide the total amount of air required per second by 
 ten and the result will represent the area of free opening required. An 
 allowance of at least forty per cent must be made when the openings are 
 covered by register-plates. For example: Suppose the amount of air 
 needed is 240,000 cubic feet per hour, sufficient to supply 100 persons with 
 the minimum quantity of air. This requires 66§ cubic feet of air per 
 second. Sixty-six and two-thirds divided by 10 is 6.6§. Adding 40 per 
 cent for obstruction of register plate, gives us 9.3 square feet as the com¬ 
 bined areas of the register-covered openings for admitting fresh air. 
 
 3. The number and location of the fresh-air inlets is not a matter of so 
 great importance as is commonly supposed. If the fresh air enters the 
 room at a temperature 20 to 40 degrees higher than that of the air of the 
 room it will go at once to the ceiling no matter where or how admitted, 
 and will thence gradually diffuse itself through the room, its course being 
 chiefly determined by the location of the windows and of the foul-air-exit 
 openings. I think it preferable that the fresh-air inlet should be in the 
 wall, near the floor, rather than in the floor, as it is by this means better 
 protected against the accumulation of dust and dirt. 
 
 In the case of large buildings containing several floors and many rooms 
 or apartments to be supplied with air, it is best not to undertake to carry 
 a separate fresh-air duct to each room, but to equalize the air pressure 
 within the building by leading large ducts to the common hall or corridor 
 of each floor, supplying each room of each floor through open transoms or 
 register plates placed near the ceiling. This arrangement secures a con¬ 
 stant supply of pure air in the halls or corridors from which each room 
 
SUGGESTIONS RESPECTING VENTILATION OF BUILDINGS, cxxi 
 
 can draw, and establishes a constant current in the direction of individual 
 users of the air, the foul air being directly removed from each separate 
 room by its own duct. This plan secures the greatest possible safety from 
 the dissemination of contagion or the dispersal of any element capable 
 of producing dangerous contamination of the air. 
 
 4. Experience has shown that in order to prevent unpleasant draft, the 
 velocity of the air at outlet openings should not be greater than five feet 
 per second. The necessary area of outlet openings is readily obtained 
 then, by simply dividing the total amount of air to be supplied per second 
 by 5. For example, suppose a room to be ventilated is calculated to 
 accommodate thirty persons, each to be supplied with 2,400 cubit feet of 
 air per hour. The aggregate amount of air to be supplied will be 30 X 
 2400 or 72,000 cubic feet. Dividing this amount by 3600, the number of 
 seconds in an hour, we have 20 cubic feet as the amount required for each 
 second. Dividing this by 5, the velocity allowable, we have 4, which 
 represents the necessary area for the foul-air outlets in square feet. 
 
 It must of course be understood that the figures thus obtained represent 
 actual opening, and not an opening partially obstructed by a grate or 
 register. As before stated forty per cent must be allowed for when the 
 opening is covered by an ordinary register. 
 
 As regards the proportion of the area of the foul-air exits to the area of 
 fresh-air inlets, it may be said that outlets should be at least double the 
 area of the inlets, since a velocity of 10 or 15 feet per second ^v be 
 allowed without injury or inconvenience at the inlet although aa Ach a 
 velocity would not be tolerable at outlet openings. 
 
 5. When a room is heated wholly or chiefly by warm air, the distribution 
 of heat in the room will be almost wholly controlled by the location of the 
 foul-air outlets. The natural course of the air current is this: the heated 
 air rises to the ceiling, spreads out, and coming in contact with the outer 
 walls which are lower in temperature than the inside walls, especially the 
 windows, it is cooled and falls to the floor. It is evident then that as the 
 outer walls and the portions of the room adjacent to them are necessarily 
 the coldest part of the room, the circulation of the air through the room 
 and the proper distribution of the heat will be facilitated by placing the 
 foul-air openings along the outer walls and preferably under the windows. 
 If the foul-air outlets are placed in an inner wall or at the floor near an 
 inside wall, one effect will be to draw toward this opening warm air which 
 ought to have been utilized in warming the outer walls. Another effect, 
 and one of the most disagreeable features attending this method of placing 
 the foul-air outlets, is that the air which has been cooled by contact with 
 the windows and outer walls and by its greater specific gravity has fallen 
 to the floor, will be drawn the whole distance across the floor to the open¬ 
 ing on the opposite side, thus constantly maintaining at the floor a stratum 
 of cold air.. An arrangement of this sort is a very frequent cause of cold 
 floors, and consequently cold feet, and the resulting headaches from 
 which the occupants of such a room are almost sure to suffer. 
 
 The foul-air outlets should be placed as near the floor as possible. The 
 opening may be in the base board or in the floor itself. The only objec¬ 
 tion to the latter method is the collection of dust which is likely to be 
 swept into the opening. 
 
 6. The ventilating ducts communicating with foul-air outlets should 
 have a sectional area equal to the free area of the openings with which 
 they communicate. This capacity should be maintained until the duct 
 
 P 
 
cxxii STATE BOARD OP HEALTH.—REPORT OP SECRETARY, 1891. 
 
 reaches the ventilating shaft, and should be increased if several turns are 
 made in the duct as each square turn has the effect to diminish the velocity 
 of the air current nearly one-half. Square turns should never be made, 
 and the ducts should be enlarged at the angles where a turn is necessary. 
 In case a duct must be carried for some distance, its capacity should be 
 increased fifty or even one hundred per cent to compensate for the great 
 amount of friction occasioned by distance. The ventilating ducts should 
 of course be made tight. For this purpose it is necessary that they 
 should be lined with metal or some other durable material. Even well- 
 seasoned lumber will shrink and open up large cracks, by which the effi¬ 
 ciency of the duct will be very materially diminished. It is also a wise 
 plan to construct ventilating ducts of some non-combustible material, or 
 at least to line with such material as a caution against fire. 
 
 Only ducts coming from the same room or floor should be connected 
 with a common ventilating shaft. Each story must have its own foul-air 
 shaft; otherwise the counter drafts occasioned by the opening of doors 
 and windows, especially in moderate weather, or the adverse influence of 
 winds, will be certain to lead to contamination of the air of one room by 
 the air of another room with which it is in communication through the 
 common shaft. 
 
 It is of the utmost importance to supply each floor, and if possible each 
 room, with its own independent ventilating shaft running as directly as 
 po^r n A to the open air without any connection with other ducts. 
 
 r . v ?e location, sectional area, and height of the ventilating shaft, are 
 questions of very great interest and practical importance. As regards 
 location, it is always better that the ventilating shaft should when possible 
 be located within the building, as in an inside wall; this insures a temper¬ 
 ature equal to that within the building, and so secures a constant and 
 positive draft, whenever the building is supplied with artificial heat. If, 
 in addition, the vetilating shaft can be located adjacent to the chimney, 
 or if the smoke can be carried up through it by means of a boiler iron 
 stack or a stack constructed of sewer pipe, a still higher temperature 
 of the air in the ventilating shaft and hence a better draft will be 
 secured. 
 
 The sectional area of the shaft will depend upon the amount of air to 
 be removed and the height of the shaft. 
 
 By a careful study of the tables of Parke and others, I have been able 
 to construct a simple formula which is of great practical service in deter¬ 
 mining these two questions. The following is the formula: The square 
 root of the height of a shaft, multiplied by the square root of the differ¬ 
 ence in temperature between the air in the shaft and the outside air, 
 divided by four, equals the velocity of the air in the shaft in feet per sec¬ 
 ond. In using this formula, it is of course necessary that two of the 
 quantities should be known. The difference in temperature is a pretty 
 constant factor. In fixing this the minimum difference should of course 
 oe chosen rather than the maximum, as a ventilating shaft which may have 
 an ample capacity in extreme cold weather when the great difference between 
 the external and internal air would secure a powerful draft, would be quite 
 insuffcient to supply the necessary amount of air in moderate weather. I 
 have chosen as a basis for obtaining the minimum difference in tempera¬ 
 ture, the tempertuare of 45° F. for external, and 70° F., the usual 
 internal temperature. At a temperature much higher than 45 degrees, 
 doors and windows are likely to be opened and hence the working of any 
 
SUGGESTIONS RESPECTING VENTILATION OF BUILDINGS. cxxiii 
 
 ventilating apparatus would be interfered with. The difference between 
 45° and 70° is 25, which may be fairly taken as a basis for calculation. 
 
 The height of the ventilating shaft is usually determined by the archi¬ 
 tect, who considers it with reference to the architectural effect in the 
 building. When this is given, we have but to take the square root of the 
 known height of the chimney, multiplied by the square root of 25 which 
 is 5, divide the product by 4 and you have as a result the velocity at which 
 the air will travel in the shaft in feet per second. It only remains to 
 divide the total number of cubic feet to be removed per second by the 
 velocity of the air per second, and the result is the sectional area of the 
 shaft which is sought. Let us take a simple example by way of illustra¬ 
 tion. Given the height of the shaft 50 feet, and the amout of air to be 
 furnished 72,000 cubic feet per hour or 20 ft. per second, the formula 
 would work out thus: 
 
 VsoxV25 _y e p j n ft p er sec. = 9 ft. ^-=2.22 sq. ft., the necessary sectional 
 area of the shaft. 
 
 If the area of the ventilating shaft is given, the height being left to be 
 determined, it is only necessary to know the amount of air to be 
 removed, the difference between the internal and external temperatures, 
 and to fix upon the velocity at which the air shall travel. The sectional 
 area of the shaft must often be determined by the conveniences of 
 construction, being governed by the plan of the building. A very safe 
 rule is to make the sectional area of the ventilating shaft equal to 
 the combined sectional areas of all the ducts leading into it. It is possible 
 to secure efficient ventilation with a ventilating shaft which is somewhat 
 smaller than this, but this is unquestionably the safest rule to follow. To 
 determine the rate at which the air will travel, it is only necessary to 
 divide the amount of air in cubic feet required per second, by the sectional 
 area of the shaft expressed in feet. With these data the determining of the 
 required height is a very simple problem, using the formula which has 
 already been given. An example will make this entirely clear. 
 
 Let us suppose that the conditions are as follows: air is required for 
 48 students. At 2,400 cubic feet per hour for each, the total amount needed 
 would be 115,200 cubic feet per hour, or 32 cubic feet per second. The 
 combined area of ducts of sufficient size to allow the transmission of this 
 air at the rate of 5 feet per second would be 32-^ 5 = 6.4 square feet, and the 
 velocity will of course be 5 feet. The question we have to solve is what 
 would be the necessary height of the ventilating shaft to secure this 
 velocity, the difference in temperature being 25°F. The solution of this 
 very practical problem is extremely simple. Bearing in mind the formula 
 we will let H represent the height of the shaft, D the difference between 
 the internal and external temperatures, and Y the velocity of air per 
 
 second; Y^y . 0 — V. Substituting the quantities which are known we have 
 
 the following: ^ H *Y? 5 =5. Beducing we have 5Vh=20; Vh=4; 11 = 16; 
 
 that is, the height of the shaft required by the conditions named would be 
 16 feet. In most instances it is more convenient to employ a smaller shaft 
 and one of greater height. Let us suppose such a case, in which -the 
 amount of air required per second is the same, namely, 32 cubic feet per 
 second, and the sectional area of the shaft 4 square feet instead of 6. Divid¬ 
 ing the amount of air required per second by the area of the shaft we have 
 
cxxiv STATE BOARD OF HEALTH.—REPORT OF SECRETARY, 1891. 
 
 8 as the velocity per second (32-^-4=8.) Our formula then would be as 
 follows: V **Y* =8 reducing we have 5 Vh=32; Vh= 6.4; H=40.96. In 
 
 this case the height of the shaft would be practically 41 feet. By the 
 same method the necessary height of shaft for any given area may be 
 readily determined. 
 
 From an economical standpoint, other things being equal, it is far bet¬ 
 ter to secure increased efficiency by increasing the size of the ventilating 
 shaft rather than its height, for the obvious reason that the capacity of a 
 shaft for removal of air increases directly with the increase in sectional 
 area; whereas the velocity of the air current increases in direct ratio with 
 the square roots of the heights of the shaft, thus requiring that the height 
 of a shaft shall be quadrupled to double its efficiency, while it is only nec¬ 
 essary to double its sectional area to secure double efficiency. There is 
 also a loss by increase of friction and of cooling surface, and in the dis¬ 
 proportionate increase of expense of construction. The cost of increasing 
 the efficiency of a shaft one hundred per cent, by increasing the velocity 
 of the air current, will be very much greater than in securing the same 
 result by increasing its sectional area. 
 
 Cases occur, of course, in which the stronger draft secured by increased 
 height of shaft is essential to the efficient working of a ventilating system, 
 or the accomplishment of a specific purpose. 
 
 8. When possible to do so it is unquestionably preferable to so plan a 
 system of heating and ventilation that it will operate efficiently by the 
 aid of “ natural draft ” only. Such a system is as nearly automatic in its 
 action as any ventilating system can be made. A draft which depends 
 upon a mechanical apparatus, as a pressure or suction fan, or even upon a 
 steam coil or other form of heating apparatus in the ventilating shaft, is very 
 likely to be found defective when efficiency is most needed. I have visited 
 many large institutions provided with large ventilating fans, and have 
 never yet found one in which the apparatus was in constant operation. In 
 many cases it had been inoperative for years and was not in running order. 
 In one case I was informed that the fan was started “ whenever the odors 
 in the ward became so strong as to be very noticeable.” To my nose the 
 odors were at that moment very strongly pronounced, and yet the fan was 
 not in operation. The noses of managers and attendants become accus¬ 
 tomed to odors to the presence of which they are constantly exposed, so 
 that they cease to be a proper means of testing the condition of the air. 
 
 Some years ago the writer visited a large hospital, the air supply of 
 which, was wholly dependent upon a fan which was a pressure blower, 
 and hence so constructed that when the fan was not in operation the open¬ 
 ing for the entrance of air through the fan was very small. The fan was 
 placed in the mouth of a tunnel nearly eight feet in diameter, just about 
 the proper size for supplying air to the hospital at a moderate velocity, 
 but the opening from the fan had a sectional area of only about four 
 square feet. The hospital had been in operation for some three years. 
 The fan had never been in operation since the opening day, as it was run 
 by a separate engine and was so far from the building as to require the 
 attention of a special engineer when in use, and consequently the air sup¬ 
 ply of the hospital, which was filled with sick people of all classes, was 
 limited to the small opening described, there being no other. It is cer¬ 
 tainly unwise to so plan the ventilating system of a large building 
 as to make the inmates absolutely dependent upon the efficient working of a 
 
SUGGESTIONS RESPECTING VENTILATION OF BUILDINGS. 
 
 CXXY 
 
 mechanical apparatus of this sort. Mechanical and other means of assist¬ 
 ing “ natural draft ” are, nevertheless, valuable and, in some instances, 
 necessary accessories to a system of natural ventilation, especially for 
 large buildings, as they furnish a means by which the disturbing influ¬ 
 ence of winds may be more or less completely overcome. The writer has 
 had two large fans in use in buildings under his care for several years, as 
 occasion has required. As usually constructed and employed, however, 
 these appliances are almost useless from their inadequacy and inefficiency. 
 This is especially the case when heat in the ventilating shaft is depended 
 upon as the means of securing a strong draft, in consequence of the use 
 of an amount of heating surface quite inadequate for the work required. 
 
 Ventilating shafts which are exposed on all sides, and even those which 
 are placed in the outer walls of buildings, must be heated or furnished 
 with a fan to insure a constant draft. The amount of heating surface 
 usually provided in such cases is ridiculously small, and is not infrequently 
 so placed as to be of very little value. When it is recalled that all the 
 air supplied to a building must pass through the ventilating shaft it will 
 be apparent that a considerable amount of heat must be imparted to this 
 air to produce a strong draft in case the chimney is so situated that the 
 air loses a considerable amount of its heat before it is expelled from the 
 chimney. 
 
 From experiments which have been made (Box) for the purpose of 
 determining the heating capacity of steam pipes we know that one 
 square foot of surface of one-inch pipe (3 linear feet) will give oft' about 
 300 heat units per hour, or 5 heat units per minute under the conditions 
 in which heating is required in a ventilating shaft. Five heat units will 
 raise the temperature of 270 cubic feet of air 1° (1 cubic foot of air at 62° 
 weighs .0761 lbs. The specific heat of air is .238. 5-^.0761-^.238=276). 
 Knowing the amount of air to be transmitted by the ventilating shaft per 
 minute or second, it is easy to determine the amount of heating surface 
 required to raise the temperature of the air one or more degrees. It is 
 only necessary to divide the amount of air transmitted per minute by 276 
 to determine the number of square feet of heating surface required to 
 raise the temperature of the given quantity of air 1 F. 
 
 Taking, for example, a case in which, as in our last illustration, the 
 amount of air required to be transmitted is 32 cubic feet per second, or 
 1920 cubic feet of air per minute, we have 1920-f-276=6.95, practically 7 
 square feet of heating surface, or 21 linear feet of one-inch pipe, necessary 
 to raise the temperature of the air 1° F. To raise the temperature of the 
 air 5°, which would be quite sufficient to insure the successful working of 
 the shaft, would of course require five times as much heating surface, or 
 105 linear feet of one-inch pipe. 
 
 The most economical method possible for heating a ventilating shaft is 
 the combustion of fuel in the shaft itself. A number of years ago in 
 studying the ventilation of the House of Parliament in London, by the aid 
 of the assistant engineer who kindly conducted me through the subterra¬ 
 nean region of this great structure, I was surprised to find that the cur¬ 
 rent of air in the great towers, which are not merely architectural features 
 but constitute the ventilating shafts of the building, was maintained by 
 means of a great heap of burning coal which was placed exactly in the 
 center of the shaft upon a high platform, the top of which was at about 
 
cxxvi STATE BOARD OP HEALTH.—REPORT OF SECRETARY, 1891. 
 
 the same level as the top of the great horizontal ventilating ducts which 
 entered the shaft at its bottom. 
 
 Fuel may be consumed in a shaft by means of a stove placed in a chim¬ 
 ney, carrying the stovepipe up through it. In exceptional cases the smoke 
 may be discharged directly into the shaft; but this arrangement is not 
 always a safe one and hence cannot be recommended. The position of the 
 heater is a matter of no small importance. I have sometimes seen a steam 
 coil placed at the extreme bottom of the ventilating shaft, the first open¬ 
 ing being several feet above it. In so placing the heater there is very 
 little circulation of air, and hence its efficient heating capacity is not 
 utilized. To secure the efficient working of a ventilating shaft the heater 
 should be placed above the highest opening. It is, as a rule, not wise to 
 have openings into a ventilating shaft at different levels, but if this 
 arrangement cannot be avoided, the heater should certainly be placed 
 above the highest opening; or if a long heater, placed against the side of 
 the chimney, it should extend above the highest opening. Whether the 
 heat should be concentrated near the lower portion of the shaft, or should 
 be extended some distance along the inside wall, is a question which may 
 be differently answered according to circumstances. There is an advan¬ 
 tage in the extension of the heater some distance along the inner wall in 
 that a better opportunity is afforded for radiation, and thus for heating 
 the inner surface of the shaft, and so preventing the tendency to down¬ 
 ward currents. It should be remembered, however, that the higher in the 
 shaft the heater is placed the shorter will be the heated column, and hence, 
 from this standpoint, the less the efficiency of the heat employed. 
 
 In conclusion, the writer wishes to disavow any attempt to make, in the 
 foregoing, an extensive presentation of the subject of ventilation. Those 
 who wish to make an extended study of the subject will find the means of 
 doing so in the excellent work of Mr. Thomas Box, published by E. and 
 F. N. Spon, 12 Cortlandt street, New York city. My aim in the prepara¬ 
 tion of this paper has been to present such practical points as I have 
 gathered from a somewhat extended experience in planning the ventilation 
 of large buildings in which I have had an opportunity to live for a series 
 of years studying the result of various methods employed, and to formulate 
 a few simple rules which are useful for the working out of correct methods 
 of ventilation in all ordinary cases, and which are much less cumbersome 
 for use than the ponderous formulae of Box and others who have under¬ 
 taken to present this subject in a scientific way. I ought also, perhaps, to 
 call attention to the fact that, while the physical principles relating to 
 heating, ventilating, etc., are correctly given by Box and other authors 
 who have given much scientific data upon this subject, the suggestions 
 made with reference to the supply of fresh air are, as a rule, widely at 
 variance with the conclusions at which Parke, Angus Smith, and other 
 investigators have arrived in the study of the question of ventilation from 
 a sanitary and hygienic standpoint, and so are not to be relied upon. For 
 example, Box puts the amount of fresh air required for each person per 
 hour at 212 cubic feet, which is simply ridiculous, being less than one 
 tenth the amount shown by ample experience to be really necessary.