Feed and return pipe size

Discussion in 'Plumbers' Talk' started by Barry Edwards, Sep 4, 2017.

  1. Barry Edwards

    Barry Edwards New Member

    Hi,

    I'm looking at installing some new rads in my bungalow, I have had a plumber do some previous work, and tbh, the heating system doesn't get very hot.

    I think he has used the wrong size feed and return pipe, he has used 15mm plastic for the main run, every other plumber I have spoken to says this should be at least 22mm and this more than likely will be the main factor as to why some rads aren't heating up correctly. ( I have bled the air out of them also and tried balancing them )

    I currently have 4 Rads @ roughly 6.5KW and 16,500 BTU, I've had these in a while and not got the exact stats but I have compared similar products online to mine. I have a Glowworm 24cxi Combi boiler, with a heat output DHW Max 24KW, CH Max 18KW and Min 4.95. Plus 22m feed and return for heating.

    Half the house doesn't have rads yet as it a refurb, I'm planning on adding 4 more rads to the system totalling 6KW and 19,500BTU.

    So the total on the system once added will be roughly 12.5KW and 36,000BTU Hopefully these figures are close to accurate but a couple of rads can be possibly down sized.

    I know I can't touch the boiler/gas myself and I know there may be several other circumstances that affect the outcome but I'm just getting some idea as I can put certain pipework in ready for the plumber etc. to keep cost down.

    Soooooo......


    1. My first question is will the boiler handle it, I've been told yes but I would like a second opinion?

    2. Second question, would I require 22mm or 28mm feed and return in copper and then use 15mm to branch off to each of the rads?

    Any helpful info would be appreciated.
     
  2. andy48

    andy48 Screwfix Select

    1. Yes, the boiler will handle it.
    2. 22mm backbone would be ideal with 15mm to each radiator. You don't need 28mm for what you are proposing.
    3. 15mm should run the existing 4 radiators well enough, provided the runs are not exceptionally long and / or do not have have too many bends / elbows / tees. However, it would struggle if you add another four and roughly double the Kw requirement.
    4. Run the new part as 22mm back to the boiler, with 15mm branches to the radiators.
    5. Convert as much as you can of the existing to 22 /15 as above.
     
    KIAB likes this.
  3. KIAB

    KIAB Super Member

    Do as much as possible of the pipe work in 22mm, keep the 15mm for the drops to the radiators.
    If pipework is under suspended floor, then insulate it, to prevent heat loss, pointless heating voids.
    Fit a magnetic filter to system to collect any crud, (Magnaclean Pro 2) among the best.
     
  4. Barry Edwards

    Barry Edwards New Member

    Thanks guys, great help :)

    I've had a mess around with the desgin and placing of the pipe work, and due to certain restrictions in loft and rooms below, I have come up with this design, does it look ok to you? The branches at the top are like that as they need to go through the ceiling in the same place to feed 2 rooms to save on mess and re plastering or using crappy looking trunking.

    Heaters.png
     
    KIAB likes this.
  5. KIAB

    KIAB Super Member

    Looks ok to me.:)
     
  6. Barry Edwards

    Barry Edwards New Member

    Ok thanks for that. I'v had a little redesign, which one do you think is the best set up, they are all possbile given where stuff is going? Will one perform better than the other due to the flow or worse due to restrictions?

    Thanks


    Heater 1=1.jpg Heaters 2=2.jpg Heaters 3=3.jpg
     
  7. KIAB

    KIAB Super Member

    No need for the extra 22mm feed for 2nd radiator, just tee off one with 22mm ,22mm 15mm tee to 2nd radiator.
     
  8. Barry Edwards

    Barry Edwards New Member

    And that should feed both Rads ok?
     
  9. KIAB

    KIAB Super Member

    Here we go.

    Hope this is understandable, no idea of distance your working with, or size of the two radiators.
     

    Attached Files:

  10. Barry Edwards

    Barry Edwards New Member

    Ah got you, thanks for that, it's really helpful.

    I can hardly tell its been photo shopped ;)
     
    KIAB likes this.
  11. KIAB

    KIAB Super Member

  12. Barry Edwards

    Barry Edwards New Member

    Brilliant, that save me searching thanks.
     
    KIAB likes this.
  13. Joe95

    Joe95 Screwfix Select

    General rule of thumb and a good guideline to follow is max 2 rads on 15mm. Don't ask me why, I've just been told by a plumber...

    Make sure you understand the practise of 'balancing' a heating system. Otherwise all that 22mm will be going to waste. A search on YouTube will give you plenty of info.

    Have you got a magnetic filer installed? It's well worth doing partularly at this stage during refurb. Can't beat a Magnaclean Pro 2.

    As far as rads go, if you choose normal looking rads, the Kudox range our hosts stock can't be beaten for their value.
     
  14. KIAB

    KIAB Super Member

  15. sam spade

    sam spade Active Member

    Have you done a heat loss calculation for your house? (I assume you have insulated it to the max as part of the refurbishment.) If so, what are the numbers?

    What is the design temperature differential? (This determines the flow rate and therefore the pipe sizes.) In the past all systems were designed for an 11C differential. Condensing boilers have changed all this, so a differential of up to 20C is now recommended as it allows the boiler to run in condensing mode more often. Unfortunately this means radiators give off less heat, so larger rads have to be installed.
     

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