using microbore copper pipe for central heating

[Chris Long]

hi

I'm going to start installing a central heating system next week and had planned to used conventional 15mm pipe of which I already have experience of. Hoewever, I now realise that 8mm and 10mm pipe is widely available.

Now I'm thinking that 8mm pipe will be much easier to manipulate and lay than 15mm? It's also cheaper and the fittings, valves, joints etc seem to be widely available. I've also heard that it makes the system more efficient.

Does it all work in the same way as 15mm? Are there any problems that arise from using this size? Are there any advantages between 8mm and 10mm?

Also, I'm assuming that to connect the system to the boiler I just use a

15mm to 8mm/10mm adaptor?

Thanks for any help

Chris

[Cicero]

=============================== Your boiler will have 22mm connections so all the pipework around the boiler will also be 22mm (possibly some 15mm - look in boiler manual). The 22mm pipe will connect to a manifold from which the 8mm (or 10mm) will emerge and return.

You can buy various types of manifold so do a bit of 'googling' for some ideas. An alternative to manifolds is to use 22mm feed and return with suitable reducers (22mm / 15mm /8mm) to make the radiator connections. This sounds a bit complicated but it can provide more flexibility in layout and shorter runs of 8mm than single manifolds.

Greater efficiency is based mainly on the fact that there is less water in the system because of the smaller pipework. I think that this is a bit of a myth because most of the water is in the radiators rather than the pipework.

The choice between 8mm / 10mm depends on various possibilities. Smaller pipework is more likely to get blocked by sludge etc. but a good inhibitor should prevent this.

If you go ahead buy an external spring to straighten and shape your pipe. Both 8mm and 10mm come in a roll so you will have to un-coil it as you go.

Enough to start with - I guess others will add to or improve on what I've said.

Cic.

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[Palindr☻me]

I went for 22mm to manifolds at each floor, then ran 8mm from those to individual rads. All the 8mm runs were about the same length - if any had been significantly longer, I would have run it in 10mm.

I went for thermostatically controlled radiator valves.

Seems to work ok but a rug in front of an open log fire is better for toasting crumpets. ;)

[EricP]

You are slightly in error in thinking a microbore system is exactly the same as a 15mm one, it's not. A 15mm pipe has a heat carrying capacity of about 4Kw, but 10mm and 8mm is considerably less and you should not have more than one rad on these pipes. This means that each rad has it's own flow and return from a central point where they join into a thing called a manifold. The manifold is usually 22mm copper and there is one for all the flows and one for the returns, the manifolds go to the boiler in 22mm pipeing.

If you can imagine two 22mm pipes going from the boiler to a convenient point and ending in two manifolds. The 8mm or 10mm pipe then comes from spiggots on each manifold to each rad.

A couple of small rads can be put on one micro flow and return, if the heat requirement is low.

As you have probably worked out, a microbore system is hideous to look at unless concealed under a floor or something.

[Chris Long]

thanks for the replys, don't seem to be able to find any manifolds online. i've tried screwfix and plumbworld, any ideas?

chris

[Cicero]

================================== I can't find the larger type - maybe they've gone out of fashion. These are actually much easier to use:

or here:

My earlier suggestion would use these two soldered together :

Cic.

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[mark]

Yorkshire Fittings manufacture the manifolds.They have an excellent site showing their complete range of fittings.Can1t remember if is .com or co.uk Mark.

>

[Cicero]

================================ This is it - very good.

Cic.

[Phil]

There are also limitations on pipe length. The bigger the rad, the shorter the permissible run. For 8mm its less than 10mm, which of course is less than 15mm. You can also run into issues with the pump not being powerful enough to push the water through because the smaller pipes have a MUCH greater resistance.

My suggestion, if you don't understand all that, is to stick with the

15mm, but consider using plastic pipe. Its so much easier to work with. If you war to persist with microbore, a Google into uk.d-i-y should get you started, and a post there would get you more specific responses.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me