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I am extending my house with a 2 storey increasing kitchen/dinning and adding extra bedroom and a bathroom. This will give me a big house with 5 bedrooms. The current house has central heating etc. Although my builder will be doing the plumbing I want to make sure I have the right system correctly installed. I will be buying new boiler and cylender. I have been advise to go for 33kw Boiler and 210 L main fed cylender. Can someone advise if:

1) Is it ok to fit the new system to the current system (I think the current one has 10mm pipes)

2) It's ok to use plastic pipes rather than copper?

3) My builder says I should go for 10mm plastic pipe otherwise he will have problem with plastering. Is he right or should I go for 15mm.

Any advise will be welcome. This extension has given me a lot of headace with things going wrong. Thanks.

Builders always do the easiest thing for them.

What I think you need is a good boiler, something like an Ariston or a Baxi gas boiler with a 5-year guarantee.

33kw seems a bit low for a 5-bedroom house, so I think a Worcester conventional green star 40 cdi would be your best bet.

Pipes should be copper, 15/22mm, don’t let them solder the pipes, use compression fitting, all the new heating boilers are moving towards high pressure boilers.

Solder pipe are only good for 3 bar, compression fittings are good for 20 bar.

Don’t use 10mm plastic or copper its nothing but trouble.

The 210-litre hot water cylinder sounds a bit like indirect unvented hot water system.

There good systems to have and give you mains pressure hot water for hours. (Good for teenagers).

Look for something like a Flamco supastor with a 25-year guarantee.

Don’t buy cheap radiators; they’re a waste of money.

Myson are the brand leader and all parts fit them.

Make sure that the heating controls are easy to use and fool proof.

And ask your council about heating grants you could get a reduction.

Hi Peter,

thanks a lot for you advise. It's the best detailed advise I have had so far. Can I just clarify, are you saying I should not go for plastic pipes even if it's 15mm. Can plastic pipes not take the pressure in the pressurised system?

The problem I have is my builder is doing everything himself and it seems he will be laying the pipes and get a 'corgi' plummer to fit the gas. He's saying he can only fit plastic pipes in the price. I will be buying all the bits like boiler etc. Basically he's no help and I have a contract for him to do the plumbing.

I will also have to work out the size of radiators. I have checked on internet for cals and I found all of them gives me a different BTU for the radiators.

Not sure if I should get another plumber to get it right or whether to let him do his way? I will look at the range you have suggested.

I think he is going to use hepworthH20 or similar.

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