Will Air in line effect heat output

Discussion in 'Boiler Forum' started by tom3holer, Apr 15, 2013.

  1. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    I have have a new installation with 3 zones each fed with their own zone pump. It seems that in the upstairs zone there isn't much heat comming out of the BB even with 160* water. I am thinking tht perhps there is air in the line. I do not hear any noise of water running. I just cleaned all the BB removing dust and dog hair. The BB are in the order of 30-40 years old. Do they tend to loose the ability to raidiate heat with age?

    Tom
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,993
    Location:
    New England
    If there is any air in the system, it will tend to naturally rise to the highest point(s). The average circulator does not have enough head to pump without water falling down the backside (return) of the loop, so you have to purge all of the air out. If you don't have purge valve(s) upstairs, it can be tedious to get it all out.
  3. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Jim,

    Thank you for the reply. I just cleaned all the BB in the house and on th first floor there were bleedrs but none on the second floor zone. I do not hear any water running and they are warm but not as hot as I think 160* water should be. I do have a clamp on temp meter and will try that and see.


    Tom
  4. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    If you don't have any bleeders or air vents on the top floor, install something there, since the top of the system is by far the most relevant point in the system for purging air.

    With the dust kittens and dog hair out of it there's no reason why copper-pipe fin-tube wouldn't still hit it's day-1 performance numbers at age 100 years.
  5. dapoppa

    dapoppa New Member

    Messages:
    9
    Location:
    NJ
    Circulator head is not what gets water to the highest radiation, it's system pressure. Determine the height of the highest BB, divide by 2.31 and add 4. That's the system pressure required. As far as air vents go, if the circ is installed on the supply vs the return, any air in the system will be absorbed and carried back to the boiler where proper air venting will release it from the system.
  6. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,792
    Location:
    Long Island, NY
    Er, what Jim D said. Once the "backslide" on the returnis established, its an easy lift.
    get all the air out; you need a bleeder up top.
    Then again, I'm not a plumber, just a semi-retired fart arounder.:p
  7. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Thanks guys,

    There is no bleeder on the top floor. I will see about correcting that.

    Tom
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,993
    Location:
    New England
    FWIW, most installed circulator pumps do not have enough head to push water up a couple of floors until all of the air is out of the system. The ability to generate high head also means higher power, and the goal is often to minimize the power and moderate the flow rate. If the system needs it, then yes, a big enough pump can be specified, but in a residential system, that shouldn't happen too often. A smaller, slower, lower power circulator is also quieter, and is often all that's needed, but you have to get all of the air out, or it won't circulate!
  9. LamdaPro200

    LamdaPro200 In the Trades

    Messages:
    10
    Location:
    New York
    A circulator pump does not pump water. It creates a differential. Get air bound, that differential is no longer. 1PSI will lift water 2.31ft. Typical residential heating system maybe 20' from the boiler to the highest radiation. 20/2.31 = 8.66 PSI though the typical boiler feed and exp tank are factory set for 12PSI system.
  10. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Thank you for the input. I will have to install some bleeders in the upstairs zone.

    I was under the impression that the pump in a closed loop doesn't have to "lift" water as it has the same weight comming down as going up.

    Tom
  11. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,792
    Location:
    Long Island, NY
    Your impression is OK, but with the air up top, there is no water to come down. The water has to "make it over the hill" first, lol.
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