To find the amount of direct radiating surface required to heat a room, basing calculations upon 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. Cu. Ft. Bathrooms or living rooms, with 2 or 3 exposures and large amount of glass surface...................... 40 Living rooms, 1 or 2 exposures with large amount of glass surface ................................................... 50 Sleeping rooms ....................................................... 55-70 Halls....................................................................... 50- 70 Schoolrooms........................................................... 60- 80 Large churches and auditoriums.......................... 65-100 Lofts, workshops, and factories............................. 75-150

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.

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 the cooling effect of the glass and its equivalent in exposed wall surface in square feet; t = difference in degrees F. between the desired temperature of the room and that of the external air; t1 = difference in degrees F. between the temperature of heating surface and that of the air in the room; s = number of square feet of glass and its equivalent in exposed wall surface.

Then, applying rule, S =( t / t1) s other cooling surfaces; it does not provide for cold air entering the room through loosely fatting 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. It is usual to estimate about 10 sq. ft. of wall surface as equivalent in cooling power to 1 sq. ft. of glass.

The heating surface found by this rule only compensates for the heat lost by transmission through windows, walls, and

* This rule also applies to hot-water heating.