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Discuss Central Heating Pipe Sizing in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. ***Tom11***

    ***Tom11*** New Member

    Whats peoples views on what pipe size i should use in the following scenario:
    2 x 3 bed houses being converted into a 4 bed.
    13Kw heating demand fed via a Worcester 42Cdi Combi, 550Cdi high flow or 35i System boiler - Customer undecided yet although i have recommended due to hot water demand required to go with the system boiler and cylinder.

    22mm from boiler and main skeleton or 28 mm and reduce to 22mm after some of the heat load has been took off to some of the rads ?

    I was thinking 22m should be fine but upon checking through various sources i keep reading conflicting advice which is making me think possibly some 28 may be needed ?
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    22mm as heating demand is below 40kw

    I would go heat only / sys and unvented cylinder
     
    • Agree Agree x 2
  3. chris watkins

    chris watkins Plumber

    Tom, I would suggest purchasing a copy of the Domestic Heating Design Guide & reading it.
    Best £30 a heating pro like yourself will ever spend.
     
    • Winner Winner x 5
    • Useful Useful x 1
  4. ***Tom11***

    ***Tom11*** New Member

    We both know that a 4 bed 2 bath property should have sys/unvented but she is adamant she wants a combi!
    So you think 22mm could cope with 40kw of heat load ? That seems excessive to me.
    Im not saying you are wrong at all but i wouldnt have thought 22mm would cope with that much.
    On looking at various threads there is conflicting information/answers.
     
  5. chris watkins

    chris watkins Plumber

    I believe Shaun meant the 13kW from your 40kW combi.
    22mm copper will carry around 23kW at a delta T of 20degC which is what you should be designing & selecting the emitters to Tom.
     
    • Like Like x 1
  6. ***Tom11***

    ***Tom11*** New Member

    Cheers for the info and the book tip, ill have a looksi for sure
     
    • Like Like x 1
  7. bogrodder

    bogrodder Plumber GSR

    13kw heat load seems rather low for 2 x 3bed houses, are these old houses with very high levels of insulation or new build houses?
     
    • Agree Agree x 1
  8. garygvl

    garygvl GSR

    5 bed new builds on some sites are only fitting 12kw boilers.
     
  9. garygvl

    garygvl GSR

    40k combi only runs at 40k when doing hot water. not sure what worcester ouput on this combi is on heating only without looking at tech specs but expect it to be below 30k and as your heating demand is only 13k boiler will modulate down anyway so 22mm all you need
     
  10. bogrodder

    bogrodder Plumber GSR

    Yes I understand that, but I don’t think the op’s description of knocking two houses into one, will be new builds lol...but I maybe wrong.
     
  11. garygvl

    garygvl GSR

    you asked was it old or new build just making a comment about new builds
    edit.. by the way agree an estimate of 13k heat load for a conversion of two 3 beds into one 4 bed is low without a s..t load of insulation
     
    Last edited: Feb 8, 2019
  12. SimonG

    SimonG Trusted Plumber Top Contributor!!

    Sized appropriately. Or pay somebody to do it.
     
    • Agree Agree x 3
  13. ***Tom11***

    ***Tom11*** New Member

    Apart from the recommended book from Chris above,

    What methods do people recommend to calculate heat required then ?

    One of the rooms in the property is as follows:
    Dining room
    4.6m (L)
    3.8m(w)
    2.3m(h)
    Solid floor
    heated rooms above
    no windows
    2 external walls
    Cavity walls - dont think insulated.
    Probly built in the 70's
    App gave me 1400w

    I have always used the Anton app before and has always seemed fine, no complaints. But as this is quite a large property i thought id get some advice from engineers with more experience.
     
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    1.25kw estimated

    About an 80x60 k2
     
  15. Craig Watson

    Craig Watson Plumber GSR Top Contributor!!

    First off, whats going in the bathrooms? Is it 2 full bathrooms with baths and showers etc or one bathroom and one ensuite? You need to answer these questions and decide whether a combi is suited, she might be demanding a combi but it's your head if it doesn't work. Also what's her mains flow rate like? If you are installing a high flow, your going to want at least 20litres a minute coming through the mains. If your converting 2 houses are you going to utilise both incoming mains? One for the hot and one for the cold supplies? As for your heating, 13kw isnt excessive so if it's sized correctly 22mm will be fine.
     
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