1004.4 Minimum Capacity of Closed-Type Tank. The

minimum capacity for a gravity-type hot water system expansion tank shall be in accordance with Table 1004.4(1). The minimum capacity for a forced-type hot water system expansion tank shall be in accordance with Table 1004.4(2), or Equation 1004.4. Equation 1004.4 shall not be used for diaphragm-type expansion tanks.

Vt = ^{(0.00041 t - 0.0466) Vs}

(

Pa

Pf Pa Po )

(Equation 1004.4)

Where: Vt = Minimum volume of expansion tank, gallons Vs = Volume of system, not including expansion tank, gal

lons t = Average operating temperature, °F Pa = Atmospheric pressure, feet H2O absolute Pf = Fill pressure, feet H2O absolute Po = Maximum operating pressure, feet H2O absolute

For SI units: 1 gallon = 3.785 L, °C = (°F-32)/1.8, 1 foot of water = 2.99 kPa

TABLE 1004.4(1) EXPANSION TANK CAPACITIES FOR GRAVITY

HOT WATER SYSTEMS ¹

For SI units: 1 gallon = 3.785 L, 1 square foot = 0.0929 m ² Notes: 1 Based on a two-pipe system with an average operating water temperature of 170°F (77°C), using cast-iron column radiation with a heat emission rate of 150 British thermal units per square foot hour [Btu/(ft ² •h)] (473 W/m ² ) equivalent direct radiation. 2 For systems that exceed 2400 square feet (222.9 m2) of installed equivalent direct water radiation, the required capacity of the cushion tank shall be increased on the basis of 1 gallon (4 L) tank capacity per 33 square feet (3.1 m ² ) of additional equivalent direct radiation.

206 2022 CALIFORNIA MECHANICAL CODE

TABLE 1004.4(2) EXPANSION TANK CAPACITIES FOR FORCED

HOT WATER SYSTEMS ¹

For SI units: 1 gallon = 3.785 L Notes: 1 Based on an average operating water temperature of 195°F (91°C), a fill pressure of 12 psig (83 kPa), and an operating pressure of not more than 30 psig (207 kPa). 2 Includes volume of water in boiler, radiation, and piping, not including expansion tank.