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

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  1. Dickspanner

    Dickspanner New Member

    Hi, new to forum and would like a bit of advice if possible.

    I have a heating system and a plumber has said I need to increase pipe diameters.

    I am confused by this as I can not make numbers stack up to justify the diameter increase.

    I have a 22mm diameter feed into a manifold which has 4 16mm diameter pipes feeding radiator network. Each branch has either 3 or 4 radiators on.

    The valves on radiators have 8mm internal opening.

    When I crunch flow and velocity through pipes etc the total still I'd greater than supply.

    I can not understand how increasing from 16 to 20mm will improve system as radiator all heat up very quickly with current configuration.

    Cheers

    Dickspanner
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    It's the capacity of the rads (kw) are probably more than the capacity of the pipes

    15 mm normally around 5kw max but if you have mlcp pipe this will be down to 4kw
     
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  3. Dickspanner

    Dickspanner New Member

    Cheers for response.

    Each branch has a maximum of 4kw on it.

    The pipes are plastic rather copper.

    Regards.

    Dickspanner
     
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Would say there fine and if your happy with how it's running I would leave it alone

    Why did you call a plumber out if you don't mind?
     
    • Agree Agree x 1
  5. Dickspanner

    Dickspanner New Member

    I have a complex hybrid system that I want modifying. It is a long story.

    Basically, I want to bypass a part of my system and the engineer said he would not connect the oil fired boiler to the distribution manifold for radiators unless pipe diameter increased.

    Cheers.
     
  6. Best

    Best Trusted Plumber Top Contributor!!

    Got to note that pipes can carry enough heat needed to radiators in warmer weather, as much less heat loss, but in depths of winter same pipes, if too small, will not get radiators up to full heat.
    Plastic pipes have smaller internal bore compared with copper equivalent.
     
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    • Like Like x 1
  7. Sparkgap

    Sparkgap Active Member

    What rating is the boiler? If it's more than about 17kW you'd need to think about 28mm from it to the distribution. You can get higher flow rates through the pipes but run into issues with noise and pressure drop and if it has a built-in pump, higher resistance with smaller pipes might mean you don't get the recommended flow through the boiler.
    So far as the rest of the system is concerned, if you've 4 circuits at 4kW each and 80/60C flow and return then 22mm copper feeding them is okay. 15mm copper gives about 5kW. Internal diameter of plastic is a bit less so I'd drop the capacities of the pipes a bit.
     
  8. Dickspanner

    Dickspanner New Member

    Hi,
    Thanks for response.

    The plastic pipe has a internal bore of 13mm. At present the manifold is fed by 22mm from storage tank but the intention is to bypass the storage tank and connect the boiler straight to the radiator manifold and underfloor manifold to give instant heat from the oil boiler instead of drawing heat from the heat exchangers in the storage tank.

    I do have a picture of current configuration but do not know how to put a picture on the thread.

    I am willing to increase the diameter of pipes from manifold but this will cost circa 1k and when doing the maths of flow vs velocity I am struggling to see benefit of bigger pipes.

    Boiler is 22.5kw oil fired.

    Sorry if my questions are stupid but I am trying not to spend 1k if I do not need to.

    Cheers

    Dickspanner
     
  9. Dickspanner

    Dickspanner New Member

    Hi,
    Thanks for response.

    The plastic pipe has a internal bore of 13mm. At present the manifold is fed by 22mm from storage tank but the intention is to bypass the storage tank and connect the boiler straight to the radiator manifold and underfloor manifold to give instant heat from the oil boiler instead of drawing heat from the heat exchangers in the storage tank.

    I do have a picture of current configuration but do not know how to put a picture on the thread.

    I am willing to increase the diameter of pipes from manifold but this will cost circa 1k and when doing the maths of flow vs velocity I am struggling to see benefit of bigger pipes.

    Boiler is 22.5kw oil fired.

    Sorry if my questions are stupid but I am trying not to spend 1k if I do not need to.

    Cheers

    Dickspanner
     
  10. Dickspanner

    Dickspanner New Member

  11. Vee

    Vee GSR

    Upgrading the pump could be an option instead of increasing pipe sizes...
     
  12. doitmyself

    doitmyself Well-Known Member

    Which boiler do you have (make and model no); and how old is it?
     
  13. Sparkgap

    Sparkgap Active Member

    From the description it sounds like you've got the boiler running into a buffer tank then a heating circuit from the tank to the manifold. For the rating of the boiler and assuming 20C temperature difference on the system you can get away with 22mm but the resistance is quite high and if you're using the same pump to circulate through the boiler and the rads you'd need to check you're getting the correct flow rates. Another issue would be what happens when one or more rads shut down. Do you have a bypass valve on the system to keep the flow up through the boiler?
     
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