If the system is equipped with a check valve or pressure-reducing valve in the cold water inlet line, an airtight expansion tank or other suitable air cusion shall be used. If provided, the tank shall be constructed according to the requirements of section VIII, division 1 of the ASME code, with a maximum allowable working pressure to equal or exceed the working pressure of the hot water supply boiler.
Kan. Admin. Regs. § 49-52-16