Microbore?

[The Medway Handyman]

Do they generally use 8mm or 10mm for CH?

I assume its the OD that the size refers to?

[newshound]

10 is more normal (yes, it's the OD). I think you could use 8 mm, but obviously there's more resistance. My (largish) system goes down to 10 mm, but I'm planning to replace one of the drops with 15 mm because I'm not getting the flow: radiator return pipe is almost cold after I added a second radiator in series to try to improve the output to the main living room. I suspect there's a kink or a solder blockage where the supply (or return) tees off from a 22 or 15 mm "main". Possibly another reason to stick with full size.

I don't think I'd risk 8 myself without doing the sums.

[mark]

Usually 10mm.Here`s a Yorkshire Fittings WM12 manifold.Unfortunately they think it`s a WM18.

[YAPH]

Yes OD. Systems I've seen round here have been mostly 8mm, sometimes with a bit of 10 or even 15mm.

[Gazz]

My bloody house has the lot, 22mm from the boiler to the first junction, then it goes to 15mm, which feeds 5 rads, then there's the hall rad which is on 8mm, and the bedroom rad is on 10mm, a little bit of 15mm pex from where the old boiler used to be thrown in for good measure too,

dunno exactly why, but the hall rad is the fastest to heat up when the heatings first turned on, and it chucks out a fair bit of heat, the rad is the same size as the ones in the living room which are on 15mm, thermodynamics is strange.

[The Medway Handyman]

Newish build - everything is microbore, just moving a rad about a metre.

[fred]

In article , harry writes

Oh, really?

[Dave Liquorice]

I *think* Harry is mxing up imperial water pipe sizes and the metric system. Apart from the above sentence the rest of the post makes sense and is correct.

Though I'm not sure about the electric conduit being measured by OD, the important bit there is ID...

[John Stumbles]

It says so on the internets - it must be true

[Roger Mills]

Use whatever is currently being used - just extend (or shorten) it.

There are rules of thumb about how much heat can be carried by each size of pipe without generating noise due to excessive water velocity. IIRC,

15mm is reckoned to be good for up to 6kW, so 8mm (with about 1/4 of the cross-sectional area) should be ok for about 1.5kW. You wouldn't normally feed more than one radiator of an 8mm pipe - and even then, not a very large one.

Hopefully someone will provide a reference to the official list.

[fred]

Apart from the totally incorrect answer to TMH's question, it was the perfect post ;-)

As you say, I think there is a bit of a time warp going on.

Just to confirm, modern day CH and general plumbing supply pipework in both copper and plastic is sized by o/d.

[Steve Walker]

My parents house was done with plastic microbore 40 years ago! The system was designed to use the pipe sizes to control flows and had no lockshield valves for balancing. Piping was 22mm (or 3/4") copper to the manifolds and 12, 10, 8 and even 6mm O.D. plastic to the radiators. They never suffered a blockage, but after about thirty years the pipes became very brittle and they now have a more conventional system.

SteveW

[Adrian C]

For electric PVC conduit, 20mm & 25mm is OD sez me ruler.

[ARWadsworth]

Do you know who the manufacturer of the 40 year old stuff was?

[Skipweasel]

Er - that's not the bore.

[Steve Walker]

No. ISTR that it was referred to as mini-microbore or something like that, but I don't know the manufacturer - I've just googled it and it mainly comes up with non-heating related links and the few heating ones are not at all informative.

SteveW

[Steve Walker]

He is actually correct to an extent I think. The problem is that what we refer to as copper pipe is actually technically copper tube and tubing is generally sized by the O.D., while good old steel pipe is still sized by the nominal bore.

SteveW

[fred]

That much is true but completely an elephant in relation to Dave's question about 8/10mm microbore or for that matter any domestic CH or supply pipework in current, common use.

"Newish build - everything is microbore, just moving a rad about a metre."

[hugh]

In message , The Medway Handyman writes

Used to be 8, I think 10 is more usual now.