What is head?

Discussion in 'UK DIY' started by Charles Middleton, Nov 11, 2004.

  1. What is head when talking about water systems in a house?
    How does it relate to hot/cold water and water for radiators?
    Thanks in advance,

    CM.
     
    Charles Middleton, Nov 11, 2004
    #1
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  2. Charles Middleton

    IMM Guest

    "Charles Middleton" <> wrote in message
    news:...

    > What is head when talking about water systems in a house?
    > How does it relate to hot/cold water and water for radiators?
    > Thanks in advance,


    Simply head equals pressure. In a house with tank in the loft the presure
    is "x" head. The head refferes to the height of the tank from its water
    line. The higher the more the pressure. 1 bar is approx 30 foot. If the
    tank is 30 foot above you the pressure where you are will be 1 bar. That is
    why in 3 story house when the tank is in the loft, on the 4 th floor, the
    pressure in the basement is high and on the top floor very low.

    A man I know, to increse the pressure on his shower installed another large
    100 gallon water tank in the loft. He was confued at why the pressure had
    stayed the same.

    So if you have a 4 floor house and the pump and boiler in the basement the
    pump may not reach the top floor radiators. The more bends and elbows in a
    pipe, the more the pressure is reduced, so a punmp has to be sized with the
    pipe run taken into acciount. Lots of elbows and the 20 foot head pump may
    only raise water 15 foot.

    A pump may be rated at 20 foot head. If a 40 foot clear plastic tube is
    attached to the outlet of the pump and it runs up directly vertical, if the
    pump pumps water from the same level the pump is on, the water should rise
    up 20 foot in the plastic tube.

    You must have heard the term "a head (pressure) of steam" on films, when the
    train driver or ships engineer waits for the steam pressure to build up to
    move the ship or train. Or the fireman shovels coal in like hell to keep
    "the head up" to keep up the speed.
     
    IMM, Nov 11, 2004
    #2
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  3. Charles Middleton

    Set Square Guest

    In an earlier contribution to this discussion,
    Charles Middleton <> wrote:

    > What is head when talking about water systems in a house?
    > How does it relate to hot/cold water and water for radiators?
    > Thanks in advance,
    >
    > CM.


    It's a measure of static pressure expressed in terms of the pressure which
    will exist at the bottom of a vertical column of water of specified height.
    For example, the head of water at your kitchen tap (for a stored hot water
    system) may be about 15 feet (roughly 0.5 bar in pressure terms) - being the
    vertical distance of the surface level of the water in the header tank above
    the tap.

    The static head of water in your central heating system is measured in the
    same way (assuming a vented system with a small F&E tank in the attic). The
    static head in the downstairs rads will be greater than that in the upstairs
    rads due to their relative vertical positions. In a pumped central heating
    system there will, of course, be a dynamic pressure which is exerted by the
    pump and superimposed on the static pressures.

    Hope this makes sense!
    --
    Cheers,
    Set Square
    ______
    Please reply to newsgroup. Reply address is invalid.
     
    Set Square, Nov 11, 2004
    #3
  4. Charles Middleton

    Set Square Guest

    In an earlier contribution to this discussion,
    IMM <> wrote:

    >
    > So if you have a 4 floor house and the pump and boiler in the
    > basement the pump may not reach the top floor radiators.


    That might be true if the pump was picking up its water from an
    open-to-atmosphere trough in the basement. But, of course, it isn't! It's
    being fed with a static head of water commensurate with the 4-floor house -
    and only has to generate sufficient *dynamic* pressure to overcome the flow
    losses.

    Back to your Physics text book, Mr IMM - if you ever had one!
    --
    Cheers,
    Set Square
    ______
    Please reply to newsgroup. Reply address is invalid.
     
    Set Square, Nov 11, 2004
    #4
  5. In article <>,
    IMM <> wrote:
    > So if you have a 4 floor house and the pump and boiler in the basement
    > the pump may not reach the top floor radiators. The more bends and
    > elbows in a pipe, the more the pressure is reduced, so a punmp has to be
    > sized with the pipe run taken into acciount. Lots of elbows and the 20
    > foot head pump may only raise water 15 foot.


    The *pressure* is reduced by bends and elbows, is it?

    Remind me again of what you claim to earn a living at?

    --
    *'Progress' and 'Change' are not synonyms.

    Dave Plowman London SW
    To e-mail, change noise into sound.
     
    Dave Plowman (News), Nov 11, 2004
    #5
  6. Charles Middleton

    BigWallop Guest

    "Charles Middleton" <> wrote in message
    news:...
    > What is head when talking about water systems in a house?
    > How does it relate to hot/cold water and water for radiators?
    > Thanks in advance,
    >
    > CM.
    >


    The term Head, when used in plumbing, is the height you have from a static
    feed tank which is above all other appliances. So, the higher the head of
    water, the more pressure you get in the pipes to move the water below it.


    ---
    Outgoing mail is certified Virus Free.
    Checked by AVG anti-virus system (http://www.grisoft.com).
    Version: 6.0.792 / Virus Database: 536 - Release Date: 09/11/04
     
    BigWallop, Nov 11, 2004
    #6
  7. In article <>,
    "IMM" <> writes:
    >
    > So if you have a 4 floor house and the pump and boiler in the basement the
    > pump may not reach the top floor radiators. The more bends and elbows in a
    > pipe, the more the pressure is reduced, so a punmp has to be sized with the
    > pipe run taken into acciount. Lots of elbows and the 20 foot head pump may
    > only raise water 15 foot.


    Hum, you have got a couple of different concepts mixed up here.

    > A pump may be rated at 20 foot head. If a 40 foot clear plastic tube is
    > attached to the outlet of the pump and it runs up directly vertical, if the
    > pump pumps water from the same level the pump is on, the water should rise
    > up 20 foot in the plastic tube.


    Yes, but the central heating pump is responsible for circulating
    the water in the system, not keeping the upstairs radiators filled
    up. Central heating pump only has to overcome the dynamic pressure
    drop of the system at the operating flow rate which is normally of
    the order of a few feet of head, and is not related to the hight
    of the header tank or the fill pressure of a sealed system. A
    central heating pump won't normally generate anything like the
    head required to pump water from the ground floor to a loft
    header tank or even upstairs radiators, and doesn't need to.

    --
    Andrew Gabriel
     
    Andrew Gabriel, Nov 11, 2004
    #7
  8. In article <cn0l0s$act$>,
    Andrew Gabriel <> wrote:
    > A
    > central heating pump won't normally generate anything like the
    > head required to pump water from the ground floor to a loft
    > header tank or even upstairs radiators, and doesn't need to.


    I'm trying to remember my basic physics about the maximum head an impeller
    pump can generate? I'd think it unlikely to be more than 1 bar?

    --
    *Two many clicks spoil the browse *

    Dave Plowman London SW
    To e-mail, change noise into sound.
     
    Dave Plowman (News), Nov 11, 2004
    #8
  9. In article <>,
    "Dave Plowman (News)" <> writes:
    > In article <cn0l0s$act$>,
    > Andrew Gabriel <> wrote:
    >> A
    >> central heating pump won't normally generate anything like the
    >> head required to pump water from the ground floor to a loft
    >> header tank or even upstairs radiators, and doesn't need to.

    >
    > I'm trying to remember my basic physics about the maximum head an impeller
    > pump can generate? I'd think it unlikely to be more than 1 bar?


    I can't think of a reason for a limit. It basically uses
    centrifugal force at the outer edge of a volume of spinning
    water, and if you make the diameter larger or the angular
    velocity higher, the pressure should increase. Maybe there's
    some factor I'm overlooking (cavitation)? Of course, there's
    a limit to what a 3" diameter impeller on a 100W motor in a
    central heating pump can achieve. I just looked up the spec
    of one typical heating pump, and it's 0.5m head.

    --
    Andrew Gabriel
     
    Andrew Gabriel, Nov 11, 2004
    #9
  10. Charles Middleton

    IMM Guest

    "Set Square" <> wrote in message
    news:...
    > In an earlier contribution to this discussion,
    > IMM <> wrote:
    >
    > >
    > > So if you have a 4 floor house and the pump and boiler in the
    > > basement the pump may not reach the top floor radiators.

    >
    > That might be true if the pump was picking up its water from an
    > open-to-atmosphere trough in the basement. But, of course, it isn't! It's
    > being fed with a static head of water commensurate with the 4-floor

    house -
    > and only has to generate sufficient *dynamic* pressure to overcome the

    flow
    > losses.
    >
    > Back to your Physics text book, Mr IMM - if you ever had one!


    You need to know more about heating and the many plumbers who have had to
    replace a pump with a more powerful version because the tops rads only get
    warm, or not at all
     
    IMM, Nov 11, 2004
    #10
  11. Charles Middleton

    IMM Guest

    "Dave Plowman (News)" <> wrote in message
    news:...
    > In article <>,
    > IMM <> wrote:
    > > So if you have a 4 floor house and the pump and boiler in the basement
    > > the pump may not reach the top floor radiators. The more bends and
    > > elbows in a pipe, the more the pressure is reduced, so a punmp has to be
    > > sized with the pipe run taken into acciount. Lots of elbows and the 20
    > > foot head pump may only raise water 15 foot.

    >
    > The *pressure* is reduced by bends and elbows, is it?


    What the f**k do you know about heating? err, err, er...nothing.

    > Remind me again of what you claim to earn a living at?


    Not twiddling a knob.
     
    IMM, Nov 11, 2004
    #11
  12. Charles Middleton

    Ed Sirett Guest

    On Thu, 11 Nov 2004 18:51:52 +0000, Set Square wrote:

    > In an earlier contribution to this discussion,
    > IMM <> wrote:
    >
    >>
    >> So if you have a 4 floor house and the pump and boiler in the
    >> basement the pump may not reach the top floor radiators.

    >
    > That might be true if the pump was picking up its water from an
    > open-to-atmosphere trough in the basement. But, of course, it isn't! It's
    > being fed with a static head of water commensurate with the 4-floor house -
    > and only has to generate sufficient *dynamic* pressure to overcome the flow
    > losses.
    >
    > Back to your Physics text book, Mr IMM - if you ever had one!


    Thanks. Whilst he started well when talking about the roof tanks, the plot
    got lost on CH circulators.

    IMM has some agreement with higher powers than I deal with that exempt him
    from the known laws nature.



    --
    Ed Sirett - Property maintainer and registered gas fitter.
    The FAQ for uk.diy is at www.diyfaq.org.uk
    Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
    Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
     
    Ed Sirett, Nov 11, 2004
    #12
  13. Charles Middleton

    IMM Guest

    "Andrew Gabriel" <> wrote in message
    news:cn0l0s$act$...
    > In article <>,
    > "IMM" <> writes:
    > >
    > > So if you have a 4 floor house and the pump and boiler in the basement

    the
    > > pump may not reach the top floor radiators. The more bends and elbows

    in a
    > > pipe, the more the pressure is reduced, so a punmp has to be sized with

    the
    > > pipe run taken into acciount. Lots of elbows and the 20 foot head pump

    may
    > > only raise water 15 foot.

    >
    > Hum, you have got a couple of different concepts mixed up here.
    >
    > > A pump may be rated at 20 foot head. If a 40 foot clear plastic tube is
    > > attached to the outlet of the pump and it runs up directly vertical, if

    the
    > > pump pumps water from the same level the pump is on, the water should

    rise
    > > up 20 foot in the plastic tube.

    >
    > Yes, but the central heating pump is responsible for circulating
    > the water in the system, not keeping the upstairs radiators filled
    > up. Central heating pump only has to overcome the dynamic pressure
    > drop of the system at the operating flow rate which is normally of
    > the order of a few feet of head, and is not related to the hight
    > of the header tank or the fill pressure of a sealed system. A
    > central heating pump won't normally generate anything like the
    > head required to pump water from the ground floor to a loft
    > header tank or even upstairs radiators, and doesn't need to.


    Depends. A pump will have "x" head on it inlet and oulet, in theory
    balanaced out. In practice the the boiler gets in the way and a lot of
    piping. From what you say a pump need only just move a water a little. If
    the restriction is high on the inlet, the suction side you may find there
    will be little flow, if any, at the far end.
     
    IMM, Nov 11, 2004
    #13
  14. In article <>,
    IMM <> wrote:
    > You need to know more about heating and the many plumbers who have had
    > to replace a pump with a more powerful version because the tops rads
    > only get warm, or not at all


    Likely because they're the furthest from the pump and the longer the
    pipework, the greater the resistance to the flow.

    --
    *If you don't like the news, go out and make some.

    Dave Plowman London SW
    To e-mail, change noise into sound.
     
    Dave Plowman (News), Nov 11, 2004
    #14
  15. In article <>,
    IMM <> wrote:
    > > The *pressure* is reduced by bends and elbows, is it?


    > What the f**k do you know about heating? err, err, er...nothing.


    Obviously rather more than you, though, then?

    > > Remind me again of what you claim to earn a living at?


    > Not twiddling a knob.


    You'd not last five minutes at it. It's something that requires skill. Not
    just quoting reams from websites and brochures without understanding a
    word of it.

    --
    *What do little birdies see when they get knocked unconscious? *

    Dave Plowman London SW
    To e-mail, change noise into sound.
     
    Dave Plowman (News), Nov 11, 2004
    #15
  16. Charles Middleton

    Set Square Guest

    In an earlier contribution to this discussion,
    IMM <> wrote:

    >
    > Depends. A pump will have "x" head on it inlet and oulet, in theory
    > balanaced out. In practice the the boiler gets in the way and a lot of
    > piping. From what you say a pump need only just move a water a
    > little. If the restriction is high on the inlet, the suction side
    > you may find there will be little flow, if any, at the far end.


    The important point - which you need to get into *your* head - is that this
    has nothing to do with *static* head (which is self-cancelling in a
    circulating system) - but is simply a function of circuit resistance.

    If you took all the pipework in your notional 4-storey house, and laid it
    out in one *horizontal* plane, you would have exactly the same relationship
    between pump dynamic pressure and cricuit flow as you had with the original
    vertical pipework.
    --
    Cheers,
    Set Square
    ______
    Please reply to newsgroup. Reply address is invalid.
     
    Set Square, Nov 12, 2004
    #16
  17. Charles Middleton

    IMM Guest

    "Set Square" <> wrote in message
    news:...
    > In an earlier contribution to this discussion,
    > IMM <> wrote:
    >
    > >
    > > Depends. A pump will have "x" head on it inlet and oulet, in theory
    > > balanaced out. In practice the the boiler gets in the way and a lot of
    > > piping. From what you say a pump need only just move a water a
    > > little. If the restriction is high on the inlet, the suction side
    > > you may find there will be little flow, if any, at the far end.

    >
    > The important point - which you need to get into *your* head - is that

    this
    > has nothing to do with *static* head (which is self-cancelling in a
    > circulating system) - but is simply a function of circuit resistance.


    The pump head overcomes that. Duh!
     
    IMM, Nov 12, 2004
    #17
  18. Charles Middleton

    IMM Guest

    "Dave Plowman (News)" <> wrote in message
    news:...
    > In article <>,
    > IMM <> wrote:
    > > > The *pressure* is reduced by bends and elbows, is it?

    >
    > > What the f**k do you know about heating? err, err, er...nothing.

    >
    > Obviously rather more than you, though, then?


    That is a question. Answer NO.

    Stop commenting on fields you know sweet FA about.

    Keep twiddling the knob.
     
    IMM, Nov 12, 2004
    #18
  19. Charles Middleton

    IMM Guest

    "Dave Plowman (News)" <> wrote in message
    news:...
    > In article <>,
    > IMM <> wrote:
    > > You need to know more about heating and the many plumbers who have had
    > > to replace a pump with a more powerful version because the tops rads
    > > only get warm, or not at all

    >
    > Likely because they're the furthest from the pump and the longer the
    > pipework, the greater the resistance to the flow.


    Go way....you don't say! Duh!
     
    IMM, Nov 12, 2004
    #19
  20. Charles Middleton

    Steve Firth Guest

    Dave Plowman (News) <> wrote:

    > You'd not last five minutes at it. It's something that requires skill. Not
    > just quoting reams from websites and brochures without understanding a
    > word of it.


    A palpable hit sir!

    --
    "They that can give up essential liberty to obtain a little
    temporary safety deserve neither liberty nor safety."

    -- Benjamin Franklin, 1759
     
    Steve Firth, Nov 12, 2004
    #20
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