pipe sizes for complete heating/DHW system

[pappasmurf]

Can someone pls help...... just bought a new house. After major works and extensions (Rear and Loft), (next year), will be an 8 bedroom, 4 shower room (no baths), 2 kitchens with full underfloor heating on all floors in the house.

The system will have 2 Worcester Bosch 24Ri (heat only boilers); 1 for the DHW, 1 for the Underfloor heating. No header tank.
I have already updated my mains supply from the street to 32mm poly pipe. The pressure is approx.3 bar and approx.20 lt/min.
There will be an indirect 300lt unvented megaflow cylinder feeding all the DHW (4 shower rooms,2 kitchens).

What i need to know is what size of pipework should i be feeding this circuit?.... i have always assumed that in plumbing, the bigger the better!... is this so?

I was thinking of supplying the cylinder with this 32mm MDPE pipe and then on the outlet from the cylinder feeding the house with 28mm MDPE and eventually reducing to all shower rooms/kitchens back down to 22mm and then further to 15mm. is this correct? as i am hoping to ensure good/reasonable flow rates to all services as possible espcially if more then 1 or 2 services are used at the same time.
will i also need an accumulator up in the loft conversion?.... if so what size pipework will i need for this aswell?

The underfloor heating in the entire property will be piped hot from heating manifolds using the "Wavin" brand.

 

[tamz]

I think you need to speak to a plumber (a good one) and either let them do the work or work alongside you.
You need a bit of a rethink on what you are planning.

 

[on31ll]

you will need a plumber with his unvented ticket to install the unvented cylinder. when you get a plumber round with a G3 qual he will talk you through it of how he would install it. hope this helps

 

[pappasmurf]

tamz i have spoken to 2 plumbers but these people are really thick!....they really don't know much about the science and design of a complete system!... they only know the basics!..... also can you please elaborate on what you mean about re-think on what i'm planning

 

[pappasmurf]

on31ll same reply to you aswell... pls read above .... the reason i am having 2 WB boilers is because i have just installed a new one of these boilers and so will only need one more.... hope this helps abit.

 

[Gray0689]

As said by tamz rethink what your planning and get a decent plumber in

 

[pappasmurf]

Gray0689... please please please will someone elaborate on this "rethink" what i'm planning sentence, before i call in a decent plumber!.... i thought i had listed "all" the requirements of what i think i need from a system?

 

[tamz]

tamz i have spoken to 2 plumbers but these people are really thick!....they really don't know much about the science and design of a complete system!... they only know the basics!..... also can you please elaborate on what you mean about re-think on what i'm planning

This is what the world has become unfortunately but there are still some good guys out there. You just need to sift out the dross. The job is slightly different to the norm but nothing difficult.

You should think about linking your boilers to run of a header. That way you also have a back up if one of them goes down.
You are correct in your 300 litre DHWC will be best with a 32 supply but the outlet needs sized to suit your load. Bigger is not always best, it is a waste of water, but it is much better than too small which is a waste of time. It only takes a few calculations to work out.
You should consider a secondary return (also needs sized correctly) MDPE is not used inside a house. If you prefer plastics use polypipe, hep, speedfit, unipipe or whatever you like.
Whether or not you would need an accumulator, only the man on the job can advise correctly on that.

If you put up your location there may be someone on here who would be willing to get involved. There are a few knowledgeable guys on here.
Good luck

 

[pappasmurf]

tamz thanks for your reply ... if when i call these guys over how will i know if their talking rubbish?... is there any tell tale signs that i can pick out in the conversation that will expose them as cowboys?.... actually one guy did mention not going to 32mm on the cylinder output and that 28mm should more then suffice. but neither of them did any calculations, so i don't know how they derived this information?....infact absolutely no calculations were made or discussed in their visits!
i do however have calculations from the underfloor heating manfacturers (Wavin)... but they were not able to help with full "system" design
i even did a search on yell.com to find a heating engineering design firm, but all i was getting was bog standard plumbers ... i am in the Hounslow/middlesex area. pls help

 

[snowhead]

With the size of property and number of rooms and outlets you will be having, you won't get a solution from the local 1 man plumber round the corner.
What you have is more like a small commercial setup.
You need someone with experience of DESIGNING and installing large systems.
Someone who's does hotels would be ideal, cause it sounds like that's what you have.