Provisions for thermal expansion in hot water systems

1. All hot water heating systems incorporating hot water tanks or fluid relief columns must be so installed as to prevent freezing under normal operating conditions. 2. Systems with open expansion tank. If the system is equipped with an open expansion tank, an indoor overflow from the upper portion of the expansion tank must be provided in addition to an open vent, the indoor overflow to be carried within the building to a suitable plumbing fixture or to the basement. 3. Closed-type systems. If the system is of the closed type, an airtight tank or other suitable air cushion must be installed that will be consistent with the volume and capacity of the system, and must be suitably designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate above thirty pounds per square inch [206.85 kilopascals] must be constructed in accordance with the American Society of Mechanical Engineers Code, section VIII, division 1. Except for prepressurized tanks, provisions must be made for draining the tank without emptying the system. Provisions must also be made for changing of all tanks without emptying the system. 4. Expansion tank capacities for gravity hot water systems. Based on two-pipe system with average operating water temperature one hundred seventy degrees Fahrenheit [76.7 degrees Celsius], using cast iron column radiation with heat emission rate one hundred fifty British thermal units per hour per square foot [158.25 x 10 to the 3rd power joules per .0929 square meter] equivalent direct radiation. Square Feet of Installed Equivalent Direct Radiation 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 5. Expansion tank capacities for forced hot water systems. Based on average operating water temperature one hundred ninety-five degrees Fahrenheit [90 degrees Celsius], a fill pressure twelve pounds per square inch gauge [82.74 kilopascals] and a maximum operating pressure thirty pounds per square inch gauge [206.84 kilopascals]. System Volume, Gallons Nonpressurized Tank Capacity Gallons Prepressurized Tank Capacity Gallons 100 15 9 200 30 17 300 45 25 400 60 33 500 75 42 1,000 150 83 2,000 300 165 Note: System volume includes volume of water in boiler, radiation, and piping, not including the expansion tank. 6. Expansion tanks for hot water supply systems must be constructed in accordance with the American Society of Mechanical Engineers Code, section VIII, division 1 if over five gallons in size of water and air.