Sizing pipework from combi boiler to bathrooms and kitchen

Discussion in 'Plumbers' Talk' started by JPB, Apr 18, 2015.

  1. JPB

    JPB Member

    We are having a new combi boiler fitted as part of a refurb. There will be a cloakroom (WC & basin), en suite (shower, WC & Basin), bathroom ( shower, bath, WC & basin) and the kitchen (sink, washing machine & dishwasher). The plumber has used 15mm from the boiler to all the bathrooms and hasn't started in 22mm. He says this will be fine because of the flow rates the combi will given when installed. The heating system uses 22mm for the flow and return and 15mm to the radiators. I was surprised the hot and cold doesn't need any 22mm but he assures me not and I have to assume he's correct.
    Can anybody confirm the the flow rates will be sufficient (assuming the boiler is correctly sized) when, for example, the sink is being used and someone is having a shower elsewhere please?
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    Your plumber has it right. You will always have an issue with a combi of having a shower and someone using a sink no matter what size pipes are put in.
     
    FatHands likes this.
  3. JPB, as Dave says, 15mm is correct.

    Your combi delivers water at a highish pressure (~ 3bar) so the pipe can afford to be smaller bore for the same flow.

    All 22mm pipe will do is create a larger store of cold water sitting in the pipes that'll have to be shifted before the hot gets to your tap...
     
    FatHands likes this.
  4. JPB

    JPB Member

    Thank you both for your helpful replies.
     
  5. G&W Plumbing & Heating

    G&W Plumbing & Heating Active Member

    You need to run 22mm to the tee before the boiler feed on the cold, then as much 22 cold elsewhere, 15 out of boiler, you will only get 15-16ltrs/min from hot on combi, the 22 cold allows the best effort to stop fluctuations in peak demand, if I where you I would fit an unvented cyl, a system your size with a combi is a big no no
     
    Plumberbish likes this.
  6. Plumberbish

    Plumberbish Active Member

    Agree with G&W...if you've got more than 1bathroom someone's bound to use a tap while your in the shower and you'll get cold lol...unvented all the way
     
  7. Horses for courses.

    JPB has a two shower/bathroom house - nice, but not a country mansion. Yes, anyone turning on a hot or cold tap/flushing t'loo etc when someone is having a shower is going to affect things with a combi, but a thermostatic shower should prevent anything nasty happening.

    And of course an unvented system will overcome these issues - but at what extra cost?

    In practice, how often will it be an issue running a household with a combi? I have three bathrooms/shower rooms (nahnahnanahnaaah) and two kids approaching teenage years (oops, one is 13...), and I can count on the scalded fingers of one hand how often I've gorn "BA****DS!" in the shower.

    Offer the options, gents, not your bias.
     
  8. Plumberbish

    Plumberbish Active Member

    Lol fair point...I have installed Combi's in houses like JPB's...but if I had the choice...and as long as the customer knows..my missus has a horrible habit of washing up when I'm in the shower
     
  9. chippie244

    chippie244 Super Member

    Try buying her flowers more often ;);)
     
    Plumberbish likes this.
  10. Same thing here. Except t'other way around... :oops:
     
    Plumberbish likes this.
  11. 22mm cold main to the combi is unecessary.
     
  12. G&W Plumbing & Heating

    G&W Plumbing & Heating Active Member

    No it's not? I said 22 to the tee that splits at cold to boiler & cold to where ever? It maximises your effort to stop fluctuations, if you have a cold main at 26ltrs with 22mm, your combi can deliver 15l depending on supply, if you run 15mm to 2 x bathrooms & a combi, no chance it will work as good as your reducing its ability
     
    Plumberbish likes this.
  13. Never done that.. anyway 15mm pipe will easily run 26 l/min.. Come on if the incoming main is am issue for a combi with a lower flow rate or fit tanks.
     
  14. Plumberbish

    Plumberbish Active Member

    only yesterday I did a flow rate on 15mm main and that was 15ltrs/min...all depends where you live and what you've got coming into the property
     
  15. G&W Plumbing & Heating

    G&W Plumbing & Heating Active Member

    Ive not known 15mm to ever give me 26,
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice