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Pick-up factor vs irregular piping

Fizz
Fizz Member Posts: 547
When sizing boilers the pick-up factor of 1.33 is used as the default guide, but when is it not? For example, my current system has 217sf of radiation in a single-pipe parallel system, with the vents on the dry returns of 2 loops which means that the steam has to fill the supply and return piping durning cycle. The mains have a total of 1.58 cf of volume in addition to 217 sf rad, would this require more radiation than 288 using 217x1.33?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    If all the piping which can fill with steam is insulated, the 1.33 is ample -- and factored into the boiler rating. In fact, many would suggest that 1.33 is too ample.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ethicalpaul
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,121
    @Fizz

    The sq footage or cubic footage of air in the piping has nothing to do with the pick up factor.

    The pick up factor is about 1 thing. Bringing the amount of metal (that is the weight in pounds of all the pipe and fittings installed) from it's ambient temperature up to 212 degrees.

    In the average small house with a 55 degree basement and insulated piping I think 1.33 is too much.

    I would use 1.10-1.15
  • Fizz
    Fizz Member Posts: 547
    Thanks for clarification guys! Happy Presidents' day!