Plumbing - Confused about pipe sizes.

Pauley2

Help!
I'm confused about the different pipe sizes and fittings I see both around my house and on sale in plumbers merchants and chain stores.

My heating system has fittings marked 14.7mm, 15mm, 1/2" and some (like TRV rad valves) don't have any markings. Some are marked with "I.S.", some with "B.S.", some with "Instantor". It looks like the same size copper pipe goes to all of them. I need to add more copper (or qualpex) pipe to move a rad but how do I tell for sure what size the existing pipe is so I can buy the right one? (there are no markings on it) Do I measure the outside diameter, inside diameter? What?

Also, Is it true that 14.7mm = Irish 1/2"? and that you can put an Irish 1/2" olive into a 15mm compression fitting and it will work?

And should I be concerned about buying in the large British chains (B&Q) in case they supply British rather than Irish standard?

I tried searching online and looking at every DIY manual I could find, but I couldn't find anywhere that provided the various specs. Ideally I'd like to see a cross ref between Irish Imperial, British Imperial and metric (and maybe U.S. imperial for the hell of it...)

Thanks!

ART6

Going by your post I would say that unless your system is very old all the pipes will be 15mm outside diameter, since that has been the standard for atmospheric (ie not pressurised) systems for years now. I wouldn't think B&Q would stock anything else since it wouldn't sell, and what they do stock will be both international standard and British standard, which applies in Ireland.

davidoco

You are the victim of penny pinching (or possibly pound pinching). Qualplex plastic pipe and fittings cost ?? and come in Irish sizes 1/2, 3/4 etc
Imported pipe pipe and fittings cost ?? less up to 50% and come in 15mm, 22mm etc. Plumber also then uses copper Irish sizes above ground and adapters.

"Also, Is it true that 14.7mm = Irish 1/2"? and that you can put an Irish 1/2" olive into a 15mm compression fitting and it will work?" --- Yes always with regular couplers but not always with rad valves, zone valves etc. Good habit when in doubt is to always cover the olive in a few turn of PTFE tape.

If the olive does not fit very snuggly on the pipe (copper or plastic) do not attempt to make the joint.

Hotblack Desiato

ART6 wrote: »

I wouldn't think B&Q would stock anything else since it wouldn't sell, and what they do stock will be both international standard and British standard, which applies in Ireland.

B&Q stock mostly Irish imperial fittings, and a small amount of metric. I've never seen British imperial there, but afaik the UK uses metric now anyway. I have had a similar problem, mix of original and newer pipework with different fittings. Previous house owners were DIY bodgers from hell...

I replaced pipework in my UK house in the late 80s, all metric fittings.

jack of all

I had a long reply posted, which I lost, damn it! Anyway, here goes again! Some of the advice offered here already is confusing, I believe; the Irish/ metric debate can be simply summed thus:

1. Irish 1/2" pipe is 1/2" internal diameter, 14.7mm external. Metric is 15mm external diameter.

2. Irish and metric pipe and fittings, can usually be used interchangeably without too much problem once you remember the golden rule:

"Use metric olives with metric pipe, use imperial olives with imperial pipe".

If using a 1/2" Irish pipe with a 15mm metric fitting, remove the metric olives and replace with imperial olives.

The same approach applies when dealing with metric 22mm and Irish 3/4" pipe, use like with like.

Don't be tempted to use PTFE tape to "make" a metric olive "fit" an imperial pipe. If you remember the above you shouldn't have any problems using metric or imperial pipe and fittings. Hope this helps.

Just to add to the above,

A 1/2" pipe will fit into a 15mm fitting, but a 15mm pipe won't fit into a 1/2 fitting.

Same for 3/4 & 22mm.

jack of all

Deleted User wrote: »

Just to add to the above,

A 1/2" pipe will fit into a 15mm fitting, but a 15mm pipe won't fit into a 1/2 fitting.

Same for 3/4 & 22mm.

True enough, BUT not always the case- I have regularly used 1/2" fittings to plumb in mixers on kitchen sinks, which usually come with 15mm copper tails.

Pauley2

Thanks all for being so helpful. The info you've given is just what I needed!