Large house combi v system boiler?

Discussion in 'Plumbers' Talk' started by Naesure, May 26, 2008.

  1. Naesure

    Naesure New Member

    Hi.

    I am upgrading central heating (at same time as kitchen / removing AGA etc) and I have a relatively large house, almost 30 years old, 5/6 bedrooms, 2 adults and 3 kids live there.

    My question is should I go for a combi boiler (Worcester Greenstar Highflow 440) or a system boiler? We have 3 showers, 4 toilets, only one bath in the house, I would say it is very rare that someone will be taking a bath at the same time as a shower. However it is very likely that someone will be taking a shower at the same time as someone else flushes the toilet / washing machine or dishwasher on / runs the hot water for dishes etc.

    I realise that the combi is easier to install, less hardware (no cylinder), I guess that cost wise the system boiler will be more expensive due to increased labour. However I am keen to get it right, I have heard that combi systems can provide interrupted flow (shower going cold when another toilet is flushed etc) and would be very interested to hear advice from professionals (other than my plumber) and related experiences. I have plenty of unused loft space (currently 2 cylinders in there!).

    All help greatly appreciated.
     
  2. tomplum

    tomplum Active Member

    i would advocate a unvented cylinder system, a combi would not be 'man' enought for a large house.
     
  3. HOTDOG ø

    HOTDOG ø Active Member

    Combi's are for flats and small houses with one bathroom. You would be a certifiable nutter if you put a combi in your house.

    A decent boiler + unvented cylinder will work beautifully.
     
  4. Water Systems

    Water Systems New Member

    My question is should I go for a combi boiler
    (Worcester Greenstar Highflow 440)

    Most definitely. A class act!

    We have 3 showers, 4 toilets,
    only one bath in the house,
    I would say it is very rare that
    someone will be taking a bath
    at the same time as a shower.
    However it is very likely that
    someone will be taking a shower
    at the same time as someone else
    flushes the toilet / washing
    machine or dishwasher on
    / runs the hot water for dishes etc.

    The Highflow will do it. Flow and pressure robbing is due to poor installation. Renew the cold mains maintap to a full-bore and run a dedicated <u>22mm pipe</u> to the combi. Tee off at the maintap and have all other cold supplies off this leg - this can have a flow regulator in it to ensure this leg does not rob the combi leg. Just before the combi tee off the cold supplies to the showers. Any pressure fluctuations around the combi will be minimised on hot and cold and to the showers. Get <u>pressure balanced</u> shower mixers - combi compatible means nothing.

    Put a Magnaclean filter on the return to the combi.

    What is your mains pressure and flow in litres/min. This means a bucket filling at the kitchen tap with a stop watch.

    Plumbers hate combis with a vengeance as it takes needless cylinder fitting work away from them. So ignore them.
     
  5. tomplum

    tomplum Active Member

    you're wrong again WS, this plumber loves combi's i have one in my own home, but they are not good enough for big houses,and it would be folly to install one without the right advise,and the right advise is:- get a few plumbers round for advise and quotes, then make yer own mind up,,,
     
  6. tgs

    tgs New Member

    I think the first thing here is to see what your existing showers are giving you in terms of litres per minute.

    Stick a container underneath ( a bucket will do) the shower and turn on for ten seconds. Then measure how much water is in the bucket (pinch a measuring jug from the kitchen) and multiply by six. If your showers are gravity fed then the result will probably be about 6-8 litres per minute.

    Three showers will consume about 24 litres per minute. You need to see if the cold supply to the house will give at least this much. If not the combi is the wrong choice. If your cold supply passes this test then the combi needs to be able to supply at least 18 litres per minute of hot water at 55C to supply the 3 showers all at once in winter. This is a 50C rise in temp from an estimated cold supply coming in at 5C.

    If you have gotten this far and still think the combi is the one for you then ring up the manufacturer's technical helpline and ask which sort of mixer they prefer you to use. I have found the answer has always be a thermo mixer rather than a pressure balancing one. The requirements, for example, for the Mira Combiforce would never be met with one shower operating on the a powerful combi like the one you are considering.

    Once you have gone through the above then, by all means, come back to the forum and ask some more questions.
     
  7. bun the plumb

    bun the plumb New Member

    ethos boiler
     
  8. Water Systems

    Water Systems New Member

    you're wrong again WS, this plumber loves combi's i
    have one in my own home, but they are not good enough
    for big houses,and it would be folly to install one
    without the right advise,and the right advise is:-
    get a few plumbers round for advise and quotes, then
    n make yer own mind up,,,

    The right advice is find out first before some plumbers come around and make them specify on your requirements, otherwise, as in 70% of cases, the least adequate solution, and that includes cost, will be installed.

    There are many combis around that can do two bathrooms without any fuss. The odd couple, can do three.

    Combis must be the first selection in a normal house with a rad circuit and decent mains pressure/flow.

    If you know about combis you would not be recommending expensive, potential bombs like unvented cylinders.

    BTW, combis <u>never</u> run out of hot water.
     
  9. doitall

    doitall New Member

    True Ws they never run out of hot water

    They just run out of water full stop.

    Anyone that considers a combi in this situation, has more money than sense.
     
  10. Water Systems

    Water Systems New Member

    I think the first thing here is to see what your
    existing showers are giving you in terms of litres
    per minute.

    Stick a container underneath ( a bucket will do) the
    shower and turn on for ten seconds. Then measure how
    much water is in the bucket (pinch a measuring jug
    from the kitchen) and multiply by six. If your
    showers are gravity fed then the result will probably
    be about 6-8 litres per minute.

    Are you kidding? You measure the flow rate at the garden or kitchen tap

    Poor main pressure is not good for any mains fed system, and that includes those pathetic unvented cylinders plumbers make fortune fitting, too.

    If you have gotten this far and still think the combi
    is the one for you then ring up the manufacturer's
    technical helpline and ask which sort of mixer they
    prefer you to use. I have found the answer has
    always be a thermo mixer rather than a pressure
    balancing one.

    Since when do makers know anything outside their boiler's cases? You get a pressure balanced mixer!!!]/b]

    The requirements, for example, for
    the Mira Combiforce would never be met with one
    shower operating on the a powerful combi like the one
    you are considering.


    As the Highflow does around 20 litres/min it probably will.

    Once you have gone through the above then, by all
    means, come back to the forum and ask some more
    questions.


    It is better if don't answer :) Duh!
     
  11. Water Systems

    Water Systems New Member

    True Ws they never run out of hot water

    They just run out of water full stop.

    Anyone that considers a combi in this situation, has
    more money than sense.

    He has three showers and one bath!!!! He says the likelihood of all three being on is slim. The HighFlow is perfect.

    I would go for the Mikrofill Ethos, as this is high flow and will never run out hot water. And it can have a secondary circulation loop on it. Then no problems.

    BTW, the HighFlow is a two stage flowrate boiler. When the store is exhausted it reverts to around 13 litres/min. It NEVER runs out of hot water.
     
  12. Water Systems

    Water Systems New Member

    BTW, an unvented cylinder will struggle with three showers.
     
  13. doitall

    doitall New Member

    As the Highflow does around 20 litres/min it probably will.

    That enough for the bath now what
     
  14. doitall

    doitall New Member

    Not if the mains is up to it, it wouldn't.

    With a combi its 100% hot water, whereas an megaflow is 50-50 hot and cold.

    A sludge bucket and a large plate would be better than a combi.
     
  15. Dick Puller

    Dick Puller New Member

    BTW, combis never run out of hot water............Well, unless they break down, which they well Xmas day, so no heating or hot water..........Happy hunting!!!

    If you take the advice of that arzehole Water Systems and fit any kind of combi, fit an electric shower also. Then at least you & Santa will get a warm shower.

    Heatbank or thermal store anyone???!!!

    What's tartan & smells of ****??
    Water Systems's slippers!!!
     
  16. Water Systems

    Water Systems New Member

    As the Highflow does around 20 litres/min it
    probably will.


    That enough for the bath now what

    20 litre min at 60C.

    Try running three showers and a bath from an unvented cylinder.
     
  17. tgs

    tgs New Member

    I think the first thing here is to see what your
    existing showers are giving you in terms of litres
    per minute.

    Stick a container underneath ( a bucket will do)
    the
    shower and turn on for ten seconds. Then measure
    how
    much water is in the bucket (pinch a measuring jug
    from the kitchen) and multiply by six. If your
    showers are gravity fed then the result will
    probably
    be about 6-8 litres per minute.

    Are you kidding? You measure the flow rate at the
    garden or kitchen tap

    The point here is how much HOT water is required from the combi and that means measuring from the shower. I then suggested measuring the mains inlet flow rate. Read the posts first.

    Poor main pressure is not good for any mains fed
    system, and that includes those pathetic unvented
    cylinders plumbers make fortune fitting, too.

    If you have gotten this far and still think the
    combi
    is the one for you then ring up the manufacturer's
    technical helpline and ask which sort of mixer
    they
    prefer you to use. I have found the answer has
    always be a thermo mixer rather than a pressure
    balancing one.

    Since when do makers know anything outside their
    boiler's cases? You get a pressure balanced
    mixer!!!

    DEFINITELY NOT!!!!!!! Pressure balanced shower valves are slower to operate and a lot of combis will produce an unsatisfactory shower. If you have several showers used together then you need a thermo mixer.


    The requirements, for example, for
    the Mira Combiforce would never be met with one
    shower operating on the a powerful combi like the
    one
    you are considering.

    As the Highflow does around 20 litres/min it probably
    will.

    If the highflow puts out 20l/min the the chances are that it will not conform to the Combiforce requirements with one shower operating. Too much not too little.

    Once you have gone through the above then, by all
    means, come back to the forum and ask some more
    questions.

    It is better if don't answer :) Duh!

    Much better if you check your facts first. You have a habit of not doing this and, not for the first time, I have had to point out the obvious and glaring errors in your postings. Of course, you will not see the wood for the trees in this case either.
     
  18. Water Systems

    Water Systems New Member

    With a combi its 100% hot water, whereas an megaflow
    is 50-50 hot and cold.

    Tripe! 60C comes out of them. Do you bath in 60C?
     
  19. Water Systems

    Water Systems New Member

    Todger, you are making things up again. When did they let you out of the cells?

    BTW, combis never run out of hot
    water............Well, unless they
    break down, which
    they well Xmas day, so no heating or hot
    water..........Happy hunting!!!

    Because you fit cheapo scrap!!!

    What's tartan & smells of ****??
    Water Systems's slippers!!!

    Todger, I am no Jocko. I wouldn't be seen dead in tartan. How is the Tammy? Still use it to wipe the joints.

    How much was the fine?
     
  20. Water Systems

    Water Systems New Member

    Are you kidding? You measure the flow rate at the
    garden or kitchen tap

    The point here is how much HOT water is required
    from the combi and that means measuring from the
    shower. I then suggested measuring the mains inlet
    flow rate. Read the posts first.

    You measure the flowrate at the kitchen tap and fit mixers or pressure equalisers to suit.


    Since when do makers know anything outside their
    boiler's cases? You get a pressure balanced
    mixer!!!

    DEFINITELY NOT!!!!!!! Pressure
    balanced shower valves are slower
    to operate and a lot of combis will
    produce an unsatisfactory shower.


    <u>You clearly haven't a clue.</u> The point about them is that they react within faction of a second while wax operated thermostatic mixers take many seconds. The different between being scalded or frozen.

    As the Highflow does around
    20 litres/min itprobably
    will.


    If the highflow puts out 20l/min


    It does.

    It is better if you don't answer :) Duh!

    Once again..It is better if you don't answer :) Duh!

    And let out loose on the public. :( Wow!
     

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