Mich. Admin. Code R. 408.4272 - Minimum capacity of closed-type tank

Rule 272. 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.

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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 equivalent direct radiation.

Square Feet of Installed Equivalent Direct Radiation 1 Tank Capacity 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.


Mich. Admin. Code R. 408.4272
1979 AC

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