Use the manufacturers Btu rating of the appliances and the heating value of the gas to determine the flow required, ft3 /hr. When Btu ratings are not immediately available, the values in Table 14.14 may be used for preliminary estimates. The average heating value of gas in the area can be obtained from the local gas company, but when this is not immediately available, the values in Table 14.15 can be used for preliminary estimates.
Example. A building has two 50-gal storage hot-water heaters and 10 domestic ranges. What is the maximum gas consumption that must be provided for if gas with a net heating value of 500 Btu/ ft^3 is used?
Solution. From Table 14.14,
Heat input = 2(55,000) + 10(65,000) = 760,000 Btu/hr
Maximum gas consumption is therefore 760,000/500 = 1520 ft^3 /hr. The supply piping would be sized for this flow, even though all appliances would rarely operate at the same time.
(C. M. Harris, Handbook of Utilities and Services for Buildings, and H. E. Bovay, Jr., Handbook of Mechanical and Electrical Systems for Buildings, Mc- Graw-Hill Publishing Company, New York.)