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runout versus riser size

Here's what I am doing: adding a radiator on the third floor.  Per charts in TLAOSH, I need 1" up-feed riser for counter-flow, one-pipe steam with max EDR of 45 when riser is not dripped.  Now, the radiator is a 45 EDR (10,800 BTU) and the 1" pipe will be about 20' tall, no other connections after it begins and then it will require a horizontal run-out of about 60".  Now, per chart on page 89 of TLAOSH, I need a diameter of 1 1/4" for 45 EDR (1" only handles 28 EDR in this configuration).

My question is this: do I use 20' of 1" knowing it is at its max EDR with this rad and then use the 1 1/4" on the run-out for the 60" run and then back to 1" for the last 12" of riser to the king-vented radiator?

Or, do it all in 1 1/4"?

I am thinking that:

a) 20' of 1" pipe will cost less then 20'  of 1 1/4" (or is cost difference minimal?)

and b) when I insulate it it will be a little thinner.

Thank you for all suggestions and advice,



  • Jamie Hall
    Jamie Hall Member Posts: 17,183
    The point is...

    you can use the 1" risers.  You have to use the 1 1/4" runout, otherwise the runout will bang like crazy.  The question is, do you want to?  I've seen installations done both ways, by very reputable dead men.  The advantage is probably lower cost of the smaller pipe, and possibly a little less obvious in the spaces it goes through.  The disadvantage that I can see is that it is maxed out; if You ever wanted to put more radiation in up there...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Luv'nsteam
    Luv'nsteam Member Posts: 272
    maxed out riser


    It is highly unlikely that any more radiation will ever be added.  On top of that, the horizontal run-out at 1 1/4" is only rated to 55 EDR, just ten over my radiators EDR.  This run-out will be in the ceiling so adding any more EDR would require this run-out to be replaced as well.  Therefore, I will stick with the 1" riser and 1 1/4" horizontal run-out.

    Thank you for your input.

This discussion has been closed.