Is it worth running 22mm from 20mm mains?

[SJRSJR]

Hello

I have 20mm MDPE mains on an outdoor stopcock about 8m from the indoor stopcock which is 15mm. It then goes to 22mm into the boiler and 15mm to the nearby downstairs sink. CH is all 15mm but the hot and cold to the upstairs is 22mm.

A timed bucket fill suggests a flow of 15l per minute and water pressure gauge indicates 5.8 bar.

While I’ve got renovation going on I was thinking I could re-route 22mm from the outdoor stopcock to indoors so it’s all 22mm.

I realise pressure is constant and flow will change but still not quite sure how noticeable a difference it’ll make!

 

[Harry Bloomfield]

water pressure gauge indicates 5.8 bar.

Are you sure that is correct, it is quite high pressure?

 

[JohnD]

the hot and cold to the upstairs is 22mm.

A house that has a water tank in the loft commonly has 22mm pipes to the bath taps, for a better flow that will fill the bath quickly despite low pressure.

A house with a combi boiler commonly has 15mm to the bath taps, to deliberately restrict the flow, because a combi can't deliver hot water fast.

If you ever get an unvented cylinder, it can deliver hot water very fast, so it is better not to have restrictive pipes.

 

[SJRSJR]

Are you sure that is correct, it is quite high pressure?

I tested it on the garden tap near to where the mains comes in, it was the only one that fitted the adaptor. I've marked where it came to, hope I read it correctly!

A house that has a water tank in the loft commonly has 22mm pipes to the bath taps, for a better flow that will fill the bath quickly despite low pressure.

A house with a combi boiler commonly has 15mm to the bath taps, to deliberately restrict the flow, because a combi can't deliver hot water fast.

If you ever get an unvented cylinder, it can deliver hot water very fast, so it is better not to have restrictive pipes.

At some point I'd like to add a cylinder. Frustratingly I think it used to have a cylinder as there's a old airing cupboard, but now it's just got a combi.

So I'll crack on and replace the pipe. Should I put a PRV on it? If so is there a good make? Thanks

 

[Johntheo5]

Thats massive pressure, if you do install a UVC then its max set pressure is 3.0bar via its PRV, so any final pressures at shower heads/taps etc will be a max of 3.0bar minus the losses between the PRV and the shower heads etc.
You can do your own calcs from the link, below.
20mm (15.4mm ID) of MDPE shows a dP (pressure loss) of 0.016bar/meter at 15LPM or 0.04bar/meter at 25LPM. A total length of 20M will loose 0.32bar at 15LPM and 0.8bar at 25LPM.
22mm (19.0mm ID) of MDPE shows a dP (pressure loss) of 0.0057bar/meter at 15LPM or 0.016bar/meter at 25LPM. A toal length of 20M will loose 0.114bar at 15LPM and 0.32bar at 25LPM.

Friction Loss Calculator

Calculate the friction loss in pipes for different materials using the Hazen-Williams equation.

www.omnicalculator.com

 

[Harry Bloomfield]

I tested it on the garden tap near to where the mains comes in, it was the only one that fitted the adaptor. I've marked where it came to, hope I read it correctly!

If that is where it read, then yes - 5.8bar. At that pressure, I would be concerned about pipes letting go. I would try another gauge, just to be sure, and then think about installing a pressure reducer. 5bar, is normally considered the absolute maximum domestic mains water pressure.

 

[Nozzle]

If that is where it read, then yes - 5.8bar. At that pressure, I would be concerned about pipes letting go. I would try another gauge, just to be sure, and then think about installing a pressure reducer. 5bar, is normally considered the absolute maximum domestic mains water pressure.

I run my compressed air system (10bar) through 22mm pipes, all the joints are soldered.

https://yorkshirecopper.com/wp-content/uploads/Technical-Guide-full-issue-02_14_Really2.pdf

The pipe is good for at least 39 bar at 65C, reducing with increasing temperature. Less for fittings

Nozzle

 

[Madrab]

No issue with altering the mains to 22mm, it will increase flow to the house. Change the 15mm stop tap to 22mm too, again to maximise flow. The pipework within the house up to the airing cupboard could also be increased in preparation for an unvented.

To give a outline on pipe sizes, 15mm pipe can flow a large amount of water as long as it has the pressure to do so, the only issue there will be is if the water velocity is great enough at an outlet then it will start to create turbulence within the supply pipework, which can then promote increased water noise and wear in the couplers, fittings, outlets etc. 22mm pipework flowing the same volume of water will be at a much lower velocity minimising turbulence and therefore noise and wear.

Ideally water velocity should be kept below 2m/s, the ideal being 1.5m/s

5.8bar of dynamic pressure within the domestic pipework is too high - you need to get a pressure reducing valve fitted after the mains stop tap and limit it to 3bar, no need for it to be any higher

 

[Harry Bloomfield]

I run my compressed air system (10bar) through 22mm pipes, all the joints are soldered.

https://yorkshirecopper.com/wp-content/uploads/Technical-Guide-full-issue-02_14_Really2.pdf

A domestic water system will likely have a mixture of pipe types and fittings in it, it's the lowest rated, or badly made joint which gives first. My own compressed air system runs at 10bar, and uses yellow gas piping throughout.

 

[SJRSJR]

Thanks for everyone's input. I'm off to get a PRV pdq!

Does the PRV go before ALL the pipework in the house including the boiler? I read somewhere that you should maximise the pressure going into the boiler but from what's being said here that sounds risky to me.

All the 22mm pipe is Hep, I was going to match it. Is that a problem?

 

[Harry Bloomfield]

Make sure it's a 'Pressure Reducing Valve', not a 'Pressure Relief Valve'. Don't worry about the boiler, adjust the pressure in your pipework, down to around 2 to 3bar, via the PRV.

Yes, it goes inline, before all of your internal pipework, probably by the stop tap, if you have one indoors.

 

[Madrab]

Does the PRV go before ALL the pipework in the house including the boiler?

Yes - Ideally directly after the main internal stop tap.

All the 22mm pipe is Hep, I was going to match it. Is that a problem?

Not at all, no reason not to use HEP. The fittings can be a pain though, they're meant to be demountable but at least 50% of them take the insert with them and then they're useless. I use JG fittings on HEP pipe and it's inserts, those fittings are truly tool-less and demountable every time.

 

[SJRSJR]

Further to my original question I’ve now bought a Philmac fitting to connect 20mm blue MDPE pipe to 22mm Hep20 pipe. What I forgot to buy was a 20mm pipe insert for when I cut the pipe.

I might be able to salvage one but if not does it have to be a Philmac insert? (I can get a Floplast or Speedfit one locally.) I'm not even sure what make of pipe it is and I'm getting a bit confused as to whether I should be matching the insert to the pipe or the fitting. Thanks

 

[Madrab]

All the OD sizes of the different manufacturers of pipe all follow specific standards therefore the OD's are the same, the ID's are different though and can be a little larger or smaller. Therefore the fittings are generally interchangeable as they have to be able to take either copper or plastic which all have the same OD but the inserts can be different. So it's all down to whether the insert fits the pipe nice and snugly, shouldn't be an issue with the fitting.

An example would be where HEP pipe has a slightly smaller ID than JG therefore their inserts aren't the same size and the JG inserts are really tight into HEP and the HEP inserts are loose in JG.

 

[SJRSJR]

Thanks for the explanation. I’ll see if I can identify the pipe brand otherwise it sounds like it’ll be trial and error until I get a snug fitting.