Using 22mm in the middle of a 15mm installation

[valdidshaw]

Hello

I’m tapping into my hot and cold water supply to feed a new WC and cloakroom basin I’m fitting. I need to run about 4m of pipe for each to get them into the cloakroom.

The supply I’ll tap into is 15mm and that’s how I intend to continue it. However, I have a spare run of 22mm copper pipe that I recovered from a previous gas installation.

Would it be OK to recycle this pipe, obviously with reducers at either end so it still starts and ends as 15mm, or would it cause problems in terms of flow etc? Could it cause water hammer?

I’m guessing it would be cheaper to recycle the 22mm pipe in this way rather than scrap it and buy new 15mm. That said, if I do need to maintain 15mm all the way then I’ll probably go for JG plastic instead, so if anyone knowledgeable about the current scrap rate for copper can advise if perhaps I’d be better doing that in any case then that would be great.

Many thanks.

 

[Nige F]

Ex gas pipe It`ll stink of gas forever - I did it myself once

 

[valdidshaw]

I like the smell of gas.

 

[muggles]

You'll not get much for a single length of 22mm pipe, they might not actually want to give you anything for it at all and I'm sure the cost of getting it to your local scrap merchant would mean that it's really not worth it. 15mm copper isn't all that expensive, granted it's more than plastic but the fittings are cheaper, for an installation of this size the cost difference between plastic and copper is going to be virtually nil. Do it properly, in 15mm copper all the way

 

[PRS1]

WIND UP!!!!!!!

 

[moggridgeplumbing]

Are you being serious?

For the cost of a length of 15mm pipe and a bit, is it worth recyclying a bit of 22mm inc fittings? Yeh, the cost of reusing a length of pipe in comparison to recycle value is better, but you are scrapping the barrel.

Stop being a 'tight a**s*' and do the job properly.

 

[valdidshaw]

All very interesting, but can anyone actually answer the main question?

ie. would it be problematic to have a 22mm run of pipe in the middle of a 15mm installation?

 

[Charnwood]

Probably less problematic than asking the question on here.

 

[simond]

It's always difficult answering a question objectively.

If we used an ex Gas pipe for water in a customer's house, that would be very much frowned upon.

If the pipe had been carrying town gas, arguably it could be contaminated with some nasty stuff.

If you have a combi, the use of a 22mm pipe for hot water will delay the arrival of hot water while the larger volume of water is displaced.

From the sound of it, you already have a few opinions so go with them. The scrap value of the pipe is scarcely worth factoring in.

 

[digdilem]

If you have a combi, the use of a 22mm pipe for hot water will delay the arrival of hot water while the larger volume of water is displaced.

Note - I'm not an expert in fluid dynamics, but I don't think it's that simple.

Judging from the little I learned when researching flow rates, only the center mass of the water moves in any significant way. In this instant, I imagine there would be a ~15mm column of water moving through the 22mm pipe, with 'dead' water either side lubricating it (ie, less resistance than the actual pipe wall).

Obviously there is a bigger mass of water, and induction would certainly lose some of the heat to the dead water so you are correct, but not as much as you might expect. (Anyone who is an expert, please correct me if I'm wrong!)

Because of the lubrication effect, I imagine it would reduce flow compared to 15mm, even if the pipework either side is the same. Very ugly though, and will be laughed at by anyone working on the system in the future.

However - since this is gas pipe, and there could be contaminants being passed onto potable water, this is very much a stupid idea.

 

[dcawkwell]

I'd use it for the cold not for the hot due to larger dead time for the hot water.

I don't see any problem. Any dirt in the pipe is soon going to be washed through.

 

[bengasman]

...I’m guessing it would be cheaper to recycle the 22mm pipe in this way rather than scrap it and buy new 15mm.

I'd love to have a look in your house.

 

[TicklyT]

Judging from the little I learned when researching flow rates, only the center mass of the water moves in any significant way. In this instant, I imagine there would be a ~15mm column of water moving through the 22mm pipe, with 'dead' water either side lubricating it (ie, less resistance than the actual pipe wall)......

That assumes a lamilar flow in the first place, which may not be the case. The change in cross-section at the reducers either end may also induce a turbulent flow, mixing the lamina, and increasing the rate of heat transfer to the pipe walls.
And there's more copper to warm up in 22mm than there is in 15mm.