160. The proper size of pipe is one which will furnish a sufficient amount of steam without undue fall of pressure, and at the same time will not present an unnecessary amount of surface of condensation.

It is found in practice, when steam having a pressure less than 5 pounds, by the gauge, is employed, that the proper sizes for branches to radiators are about as follows:

One-Pipe System.

 Heating Surface of Radiators. Diameter of Pipe. 24 square feet or less............... 1 in. Above 24, not exceeding 60 square feet...... 1 1/4 in. Above 60, not exceeding 100 square feet...... 1 1/2 in. Above 100 square feet............... 2 in.

Two-Pipe System.

 Heating Surface of Radiators. Steam. 48 square feet or less........... 1 in. 3¥ in. Above 48, not exceeding 96 square feet... 1 1/4 in. 1 in. Above 96 square feet........... 1 1/2 in. 1 1/4 in.

161. The preceding data apply to direct radiators; when indirect radiators, which condense more steam per square foot, are used, the area of the pipes should be increased to about as follows:

 Heating Surface of Indirect Radiators. Steam. Return. 30 Square feet or less ............................... 1 in. 3/4 in. From 30 to 50 square feet....... 1 1/4 in. 1 in. From 50 to 100 square feet...:... 1 1/2 in. 1 1/4 in. From 100 to 160 square feet....... 2 in. 1 1/2 in.

162. The size of steam mains, or principal risers, may be computed by the following rule:

## Rule Lo

Divide the amount of direct heating surface in square feet by 100; divide the quotient by .7854. and extract the square root of the quotient thus obtained; the result will be the diameter of the pipe in inches.

## Example

What should be the diameter of a main steam pipe to supply direct radiators having a total heating surface of 3,800 square feet?

Solution.

.7854 = 6.9 inches; in practice a 7-inch pipe would be used.

163. To find the amount of radiator surface which may be properly supplied by any given size of pipe, the reverse process should be followed:

## Rule 11

Multipy the square of the diameter of the pipe in inches by .7854; then multiply the result by 100; the result is the total amount of heating surface, in square feet, which the pipe will supply.

## Example

What amount of direct heating surface may be supplied by a steam pipe 7 inches in diameter?

## Solution

72 X .7854 X 100 = 3,848 square feet, nearly. Ans.