RADIATION.

Location of Radiators.-Direct radiators should be located near the outer walls, where the cooling influence is greatest. When the radiators are so located that the warm-air currents ascending from them will mix with the incoming cold-air leakage, a nearly uniform temperature will be maintained throughout the room.

Fig. 1 serves to illustrate the difference in heating results between placing a radiator under the window, and placing it

against an inner wall. The arrows show the circulation of the air.

Direct-indirect radiators are necessarily placed against the outer walls, as shown in Fig. 2, and as a rule are thereby located properly.

Indirect radiators are usually located against or near outer walls, as shown in Fig. 3. The efficiency of the radiator increases with the height of the radiator flue.

In factories and workshops heated by steam in pipe coils, it is customary to place the coils on the walls of the room and near the floor. Another common plan is to place the coils overhead, suspending them horizontally below the ceiling. The movement of machinery will usually diffuse the heated air throughout the apartment in a satisfactory manner.

FIG. 2.

Proportioning Radiation.-To find the amount of direct radiating surface required to heat a room, basing calculations on its cubic contents, allow 1 sq. ft. direct radiating surface to the number of cubic feet shown in the following table:

PROPORTION OF RADIATING SURFACE TO VOLUME

OF ROOM.

Description.

Bathrooms or living rooms, with 2 or 3 exposures

and large amount of glass surface.

Living rooms, 1 or 2 exposures with large amount

of glass surface

Halls

Sleeping rooms

Schoolrooms

Large churches and auditoriums

Cu. Ft.

40

50

55-70

50-70

60-80

65-100

75-150

Lofts, workshops, and factories.

The above ratios will give reasonably good results on ordinary work, if the engineer uses proper judgment in allowing for exposures, leakages through building, etc.

This table applies to direct radiation only. If indirect radiators are used, allow not less than 50 per cent. more surface. If direct-indirect radiators are used, allow not less

than 25 per cent. more surface. The general use of any method of proportioning radiation to the cubical contents of the rooms to be heated is not advisable. The foregoing table is presented merely for the convenience of those who may be able to use it with good judgment, and for "checking up"

purposes.

Proportion of Radiating Surface to Glass Surface Baldwin's Rule.-Divide the difference in temperature between that at which the room is to be kept and the coldest outside atmosphere, by the difference between the temperature of the steam pipes and that at which the room is to be kept. The quotient will be the square feet or fraction thereof of plate or pipe surface to each square foot of glass, or its equivalent in wall surface.

Let S

amount of radiating surface required to counteract cooling effect of glass and its equivalent in exposed wall surface, in square feet;

t = difference, in degrees F., between desired temperature of room and that of external air;

=

difference, in degrees F., between temperature of heating surface and that of air in room;

S= number of square feet of glass and its equivalent in exposed wall surface.

The heating surface found by this rule only compensates for the heat lost by transmission through windows, walls, and other cooling surfaces; it does not provide for cold air entering the room through loosely fitting doors, windows, etc., for which an ample allowance must be made. Some buildings are so poorly constructed that 50 per cent. or more must be added to the amount of heating surface obtained by the rule in order to counteract the cooling effect of these air leakages. A common practice is to add 25 per cent. for buildings of ordinary good construction. Ample allowance should be made for rooms exposed to cold winds. This rule also applies to hot-water heating.

Suppose that we have three rooms A, B, and C, as shown in the accompanying illustration, of precisely the same

dimensions, and consequently having the same cubical con tents, the rooms being each 25 ft. long by 20 ft. wide, with a 10-ft. ceiling. Let us also suppose that the halls, or corridors, D and

the other rooms in the building will be warmed to a temperature equal to that desired in A, B, and C by radiators not shown; first proceed to find, by Baldwin's rule, the