ANSI Z21.13-2017/CSA 4.9-2017

1.1
This Standard applies to newly produced gas-fired low-pressure steam and hot water boilers with gas inlet pressure ratings not exceeding 0.5 psi (3.5 kPa) and having input ratings of less than 12,500,000 Btu/hr (3 663 389 W) (see Clause 3, Definitions), hereinafter referred to as boilers*, constructed entirely of new unused parts and materials, for operation at or below the following pressures and temperatures:
Steam heating boilers 
   15 psi (103.42 kPa) steam pressure 
Hot water heating boilers