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sizing radiator mains

Timco
Timco Member Posts: 3,040
in THE MAIN WALL
Hot water or steam? Two different beasts. If HW, depends on run length and # of rads on zone. If steam, depends on type of system.
Just a guy running some pipes.

Comments

  • radmix
    radmix Member Posts: 194


    when installing a new boiler and connecting into existing radiators do you size your pipe for the heat loss of the house or do you size your pipe for the btu's of the existing radiators. this particular house has 11/2 mains feeding radiators in a 1500 sq foot house. can i reconnect using a 1 inch feed.
  • radmix
    radmix Member Posts: 194


    there hot water radiators, So I have to size the mains to the output of the radiators not to the heat loss of the house.
  • Brad White
    Brad White Member Posts: 2,399
    Feeding Radiators

    When sizing run-outs to individual radiators, typically 3/4" or 1/2" would be ample. If in doubt, default to 3/4".

    Bush down if connecting to old large gravity risers.

    1/2" and 3/4" respectively will carry 15,000 to 40,000 BTU's per hour at a 20 degree drop and twice that amount at a 40 degree drop.

    If your radiators are larger than that they would have been mentioned in the Bible.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Weezbo
    Weezbo Member Posts: 6,232
    *~/:)

    Well said :)
  • radmix
    radmix Member Posts: 194


    individual radiators are already connected to the main which is 1 1/2 copper. Heat loss of the zone is not much more than 30,000 btus. Can I connect a 3/4" pipe off of my new panel to the existing piping which is 1 1/2". I know that I can get 40,000 btu's off of that 3/4. Or is that like feeding a ocean of water with a hose.
  • Brad White
    Brad White Member Posts: 2,399
    If your load is 30 MBH

    Then go ahead and use 3/4". The pipe size to which you are connecting has no meaning except for low pressure drops.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • radmix
    radmix Member Posts: 194


    Thanks for the info Brad. This brings me to my next question,When reconnection into the main I should size my circulators for the flow rates of the 1 1/2" pipe not the 3/4" pipe coming off my panel.
  • Brad White
    Brad White Member Posts: 2,399
    Oh God no.....

    If one sized for the flow rates the piping could carry, especially old, large gravity HW piping, we would be moving as a nation more excess water than the mighty Mississippi and Nile combined.

    Just size the circulator for what the radiators need on a per-room basis. Flow is very forgiving variable(50% flow will still give you 90% of full-flow capacity).

    Just be sure you can balance the flow using really good balancing valves or that you have TRV's on all radiators. That would be best of all, each taking only what it needs.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
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