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Discuss Electrician DIY plumbing in own house, advice needed in the Plumbing Forum | Plumbing Advice area at

Hi guys, before anyone jumps to tell me “get a plumber”, I’m extending my house and doing a loft conversion myself, so looking to save money, that’s my only reason for not getting a plumber. I see mixed opinions on whether to go plastic or copper, I’m happy to learn how to join copper, but at the same time plastic is much faster and cheaper I’m guessing.

if anyone could give advice on pipe sizing and best routing for CH that’d be great, it’ll be a combi at far length of house with 6 rads (I know it’s dependant on BTU demands for rooms size/window size), house is all solid walls so I may pipe sleeve them or some sort of horse hair insulation etc.

basically any advice is welcome, thanks


Gas Engineer
22mm the main flow and return with short lengths of 15mm to the radiators. Could do the lot in plastic. Just need 1m from the boiler to be copper.


Hiya, plastic v copper an often asked question. Copper MUST be used near the boiler
plastic can be good for long runs but looks untidy when exposed and can turn yellow in time. So copper for upstands to radiators for strenght and appearance. Run the main flow and return in 22mm pipe and t off in 15 mm for the more than two on 15mm. Its quite neat to hide pipes in electrical trunking with capping and behind the hinge side of an opening door. Allow drain offs on all drops and fit a magnetic and none magnetic filter on the return to the boiler. anything else ask away centralheatking
is it worth using foil Rockwool insulation, it’s expensive but is it really much different for your standard lagging, in the situation of house plumbing.

also DHW 15mm throughout? There’s no bath.

Mains water size? Same as what’s coming in?

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