Section 408.4270. Provisions for thermal expansion in hot water systems.

(1) All hot water heating systems incorporating hot  water tanks or fluid relief columns shall be so installed as to prevent freezing under normal operating conditions.

(2)   If the system is equipped with an open expansion tank, an indoor overflow from the upper portion of the expansion tank shall be provided in addition to an open vent. The indoor overflow shall be carried within the building to a suitable plumbing fixture or to the basement.

(3)   If the system is of the closed type, an airtight tank or other suitable air cushion shall be installed that will be consistent with the volume and capacity of the system, and shall be suitably designed  for  a hydrostatic test pressure of 2 1/2 times the allowable working pressure of the system. Expansion tanks for systems designed to operate at or above 30 psi shall be constructed in accordance with the provisions of section VIII of the ASME boiler and pressure vessel code, 1983 edition, and its addenda. Provisions shall be made for draining the tank without emptying the system, except for pressurized tanks.

History: 1979 AC; 1985 AACS.