Sealed room boiler - water supply

Discussion in 'Water Heater Forum, Tanks' started by sprinkler, Nov 8, 2009.

  1. sprinkler

    sprinkler Member

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    I have a sealed room boiler (with built-in hot water tank) which takes the water supply (for hot tap water) from an attic tank. I have a system in the house which turns on the heating at around 5 degrees celcius, in the case that the house is empty and the weather gets very cold, so as to avoid bursting pipes.
    But would it be ok to also empty the water supply tank in the attic in case the temperature got low enough to burst pipes there. I have the hot water temperature set to the minimum (15 degrees - though in practice it would go above 20 degrees) and when the boiler turns on, this water heats up before the rads get hot. My doubt is whether the water level in the boiler tank might go down as the water heats and evaporates? Or should the water supply to the boiler always be available, eventhough no hot water taps are turned on? Thanks.
     
  2. Thatguy

    Thatguy Homeowner

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    In principle, if the boiler is sealed and no taps are open, the water level cannot drop.

    You have a link to your boiler?
     
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  4. sprinkler

    sprinkler Member

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    Well, the part of the system that heats the rads is sealed at a constant pressure of around 1,5 bars. But the hot water supply isn't sealed - when you turn on a hot tap, new water feeds into the boiler from the attic tank. If I empty the attic tank, I thought that some small amount of water would evaporate in the boiler as it heats, and if the attic tank is empty, new water wouldnt replace the water that evaportes in the boiler. Although I imagine that any evaporated water might actually return to the boiler if it cools down before reaching the nearest exit, which would be the attic tank?? Also, even after emptying the attic tank, water would still remain in around 6 meters of pipework to the boiler, though about 3 meters are horizontal pipe.
     
    Last edited by a moderator: Nov 8, 2009
  5. Thatguy

    Thatguy Homeowner

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    If I remember correctly, water in a heated sealed tank will evaporate until the vapor pressure of water equals the pressure in the tank.
    If the tank is effectively unsealed the water will evaporate and be lost. In that case, given the water temp. and air humidity, the rate of loss of water due to evap. can be calculated.
    Maybe I should keep my thermodynamics book, after all. . .:p
    BTW, 1,5 bars (you must be European) = 20 PSI. T & P valves in water heaters release at 125 PSI (?).
     
    Last edited: Nov 8, 2009
  6. sprinkler

    sprinkler Member

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  7. Thatguy

    Thatguy Homeowner

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    My translator doesn't do Gaelic
    http://www.oddcast.com/demos/tts/tts_tran_example.php?clients
    :(
    and your link probably doesn't have the data needed to make the calculation.
    :(

    BTW, the girl in the link will say anything you want her to, but with the wrong inflection for the content of what she's saying. It's hilarious.
    You select "Arabic" to "English" and type in English what you want her to say.
     
    Last edited: Nov 8, 2009
  8. sprinkler

    sprinkler Member

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    But the link I posted is in English.
     
  9. sprinkler

    sprinkler Member

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    I just called Domusa (who make the boiler) and they say it's no problem to empty the attic tank, and that in any case there is a security valve on the boiler, through which the water supply enters, and this valve only allows water to travel into the boiler, not to return. This security valve also opens in case the boiler pressure reached 7 bars. So I think the problem is resolved. Thank you.
     
  10. sprinkler

    sprinkler Member

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    But ..just thinking again - I still think some hot water could evaporate because the hot water normally goes out of the boiler to the kitchen, bathroom etc, where the faucets would be turned off BUT possibly some evaporation could escape back into the attic tank? Then maybe the solution would be to close the valve on the supply line from attic tank to boiler?
     
  11. Thatguy

    Thatguy Homeowner

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    It must have been the rum talking/posting. :p

    You could run an experiment to determine what loss you have over time, if any, if you can measure water levels precisely.
     
    Last edited: Nov 9, 2009
  12. sprinkler

    sprinkler Member

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    Yea, but the hot water tank is inside the boiler, so there's no way to measure the level that I can think of. In any case I think the best solution would be to empty the attic tank IN CASE the weather gets cold enough to burst pipes there, to avoid having a "swimming pool" in the house. Although I do have the attic pipes well insulated...Thank you.
     
  13. nhmaster3015

    nhmaster3015 Master Plumber

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    Fill the boiler with a mixture ofr glycol and water and forget about it.
     
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