An expansion tank shall be installed in every hot water system. For multiple boiler installations, a minimum of one expansion tank is required. Expansion tanks shall be of the closed or open type. Tanks shall be rated for the pressure of the hot water system. Lockable shutoff valves shall be installed at connections to all expansion tanks. Valves shall remain locked in the open position.
Closed-type expansion tanks shall be installed in accordance with the manufacturer's instructions. The size of the tank shall be based on the capacity of the hot-water-heating system. The minimum size of the tank shall be determined in accordance with the following equation:
For SI:
where:
For SI:
where:
| Vt | = | Minimum volume of tanks (gallons) (L). |
| Vs | = | Volume of system, not including expansion tanks (gallons) (L). |
| T | = | Average operating temperature (°F) (°C). |
| Pa | = | Atmospheric pressure (psi) (kPa). |
| Pf | = | Fill pressure (psi) (kPa). |
| Po | = | Maximum operating pressure (psi) (kPa). |
Open-type expansion tanks shall be located a minimum of 4 feet (1219 mm) above the highest heating element. The tank shall be adequately sized for the hot water system. An overflow with a minimum diameter of 1 inch (25 mm) shall be installed at the top of the tank. The overflow shall discharge to the drainage system in accordance with the New York City Plumbing Code.