It is assumed in the following rules and tables that the average temperature of the hot air in the flues is about 120°, and that the air is moved solely by natural draft.

A simple method for proportioning hot-air pipes to deliver a given volume of air to the several floors is to assume that 1 sq. in. of stack, or flue, area will supply 100 cu. ft. of air per hour at the first floor, 125 at the second floor, and 150 at the third floor.

## Ratio Of Area Of Hot-Air Pipes To Volume Of Room

 Rooms. Ratio. 1 Sq. In. to Cu. Ft. First-floor rooms, moderate exposure............ 30 First-floor rooms, great exposure ................... 20-25 Second-floor rooms .......................................... 25-35 Third-floor rooms............................................. 30-40

A more accurate method is as follows:

### Rule

For rooms on the first floor, add together the total glass surface and 1/4 the area of the exposed walls in square feet, and multiply the total by 1.5; the product is the proper area of the pipe in square inches. For second-story rooms, multiply by 1 to 1.25, according to the exposure; and for the third story, by .75 to 1.

If leaders are of considerable length, their area should be about 1/4 greater than the connecting stacks.

## Size Of Hot-Air Pipes And Registers

 First-Floor Rooms. Second-Floor Rooms. Size ofRegister.In. Diameter of Pipe. In. Size ofRooms.Ft. Height ofCeiling.Ft. Size of Register. Diameter of pipe. In. Size ofRooms.Ft. Height ofCelling.Ft. 12 X15 12 16X16 11 10X14 10 16X16 10 to to 18X20 18X20 10X12 10 14X14 10 9X12 9 14X14 9 or to to 10X14 15X15 16X16 9X12 9 12X12 9 8X12 8 10X10 8 to to 14X15 13X14 8X12 8 8X12 9 8X10 7 7X12 8 to to 13X13 12X12