A few questions about changing microbore & radiators

Discussion in 'Plumbing and Central Heating' started by Sard, 2 Sep 2020.

  1. Sard

    Sard

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    Hi all,

    I'm currently in the thick of renovating my house and have my floorboards up. I'm looking to install some new radiators and notice that I have 8mm microbore, which I am keen to replace so that I won't have to worry about it in the future. The Flow & Return pipes are 15mm otherwise and the tee off to each rad is 8mm.

    I would like to avoid having to cut a chase out for each downstairs radiator, but equally I know I dont have enough height above to drop in 2000mm copper pipe between the plasterboard & wall. Therefore my plan is to tee off from the F&R pipes using copper and put a 90 degree bend close to the wall, attach a compression fitting coupler and then run a length of plastic pipe down to the rad, attach another compression fitting coupler and finish it in copper with a 90 degree bend out to my right angle TRV valves. For my upstairs radiators, I won't need to use plastic and will do the job in copper 15mm.

    I also plan to mark up my rads, attach the brackets and cut my lengths and do my bends the day before, so I can get the job done in a day. In light of the above, I would really appreciate some guidance on the following:

    1) Does this sound like a reasonable approach?

    2) Are there any issues with me replacing 8mm with 15mm piping? There will be 4 rads in the house where the pipes are not accessible and therefore will remain on 8mm microbore.

    3) If I use plastic pipe in between the wall cavities, will it require sheathing/insulation or clipping? I would aim to clip at the top and close to the rad anyway (approximately 2.4m apart). The upstairs radiators will be fitted with copper piping throughout, as they are closer to the floor, but I am wondering if I will need to sheath/insulate and clip the pipes? I'm concerned about getting enough depth to attach clips around 15mm pipes.

    4) For my plastic pipe, I was looking at using 'FloFit FPX15B/25 Push-Fit PE-X Barrier Pipe - White 15mm' from screwfix and I would like to check if the inserts I need for the compression fittings are proprietary to each type of pipe manufacturer or can I use any 15mm pipe insert?

    Thank you in advance :)
     
    Last edited: 2 Sep 2020
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  3. Madrab

    Madrab

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    How many radiators in total + average size of radiators?
     
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  4. Sard

    Sard

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    13 rads in total.

    Highest would be a 4000 BTU 1800 X 350 double panel rad and the smallest being a 600 X 400 single panel 1400 BTU rad
     
  5. oldbutnotdead

    oldbutnotdead

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    Inserts are specific to the tube (so use the inserts made by the tube supplier).
    Hidden compression fittings are best avoided- rather like hidden push-fit fittings. I've had zero problems with the JG fittings I've fitted (but have had problems where others have installed), end of the day its your call.
    Securing the tubes is always a good idea, insulate them if they're in a cold void and/or running along cold water pipes.
     
  6. Madrab

    Madrab

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    I think you need to be careful, 15mm main flow and returns will struggle to supply enough heat for all those rads.

    With 13rads you really need 22mm main feeds (F & R).

    It has been ok up till now as the rads were all on 8mm so the 15mm mains could probably cope albeit probably took a while to heat all the rads up? If you up the rads to 15mm then you'll probably find that all the rads won't heat up properly without a very specific and careful balancing exercise.
     
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  8. Sard

    Sard

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    Thank you. What would be the best means of insulation for a shallow wall cavity? Would it be the standard foam wraparounds?
     
  9. Sard

    Sard

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    Thank you for the guidance. So far our system has been working well and heats up fairly quickly. I'd say within 5 or 10 mins and the rads are quite warm to touch. If I was to leave the microbore in, where I am installing the big rad, should I fit with 15mm or stick to 8mm?
     
  10. oldbutnotdead

    oldbutnotdead

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    If it'll fit, yes. If the wall cavity (not the dry lining cavity) is insulated then energy from the pipes will mostly go into the room rather than to waste so don"t get too worked up about it (do seal the drylining cavity at the top though, gaps there can cause draughts).
    Good point by @Madrab, 15mm backbone isn't really up to delivering the heat to those rads at acceptable water velocity.
     
  11. oldbutnotdead

    oldbutnotdead

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  12. Sard

    Sard

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    Thank you. Would it be a reasonable compromise to use 10mm pipes for the 4 rads that I'm moving, given the existing 8mm microbore for these rads will need to be re-routed and probably replaced. I could then leave everything else untouched?
     
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