Section 408.4272. Minimum capacity of closed-type tank.

The minimum capacity of the closed-type expansion tank may be determined from tables 272A and 272B or from the following formula where the necessary information is available.

Vt = (0.00041 T-).0466Vs

Pa  -  Pa Pf - Po

Where:  Vt = minimum volume of tanks, gallons

Vs = volume of system, not including tanks, gallons

T  = average operating temperature, degrees Fahrenheit Pa = atmospheric pressure, psia

Pf = fill pressure, psia

Po = maximum operating pressure, psia

Table 272A

Expansion Tank Capacity for Gravity Hot Water Systems Based on 2-pipe system with average operating water temperature 170 degrees Faherenheit, using cast iron column radiation with heat emission rate 150 Btu per hour square foot equivaelnt direct radiation.

Square Feet of Installed                Tank Capacity Equivalent Direct Radiation 1           Gallons

Up to 350	18
Up to 450	21
Up to 650		24
Up to 900	30
Up to 1,100	35
Up to 1,400	40
Up to 1,600	2 - 30
Up to 1,800	2 - 30
Up to 2,000	2 - 35
Up to 2,400	2 - 40

1 For systems with more than 2,400 square feet of installed equivalent direct water radiation, the required capacity of the cushion tank shall be increased on the basis of 1 gallon tank capacity per 33 square feet  of additional equivalent direct radiation.

Table 272B

Expansion Tank Capacities for Forced Hot Water Systems Based on average operating water temperature 195 degrees Fahrenheit, a fill pressure 12 psig and maximum operating pressure 30 psig.

System Volume, Gallons 1        Tank Capacity, Gallons

100	15
200	30
300	45
400	60

500	75
1,000	150
2,000	300

1 Includes volume water in  boiler,   radiation,   and   piping,  not  including expansion tank.

History: 1979 AC.