32mm mdpe or 25mm

[Madrab]

Did you mean this thread

Yup @Hugh Jaleak, it would help if I actually put the link to the thread into the post wouldn't it .... DOH!!

 

[Londoner2]

I was faced with this last sept.

In the end 25mm was put in and no issues. We used a Thames WATER approved contractor who said i can put in 32mm if i want but will not make a difference if your internal pipes are 15mm. We have 25mm mdpe, then about 1.5m of 22m copper then a 15mm t junction for the rest of teh house.

 

[Madrab]

will not make a difference if your internal pipes are 15mm

It's a big failing of a lot of installations where people cut their distribution pipework to 15mm as it's easier/cheaper to install.

A lot of people don't realise that the outlet experience (how good the water coming out of the tap is personally appreciated) is to do with water velocity (noise) and resistance (pressure and flow reducing friction), not just the flow and pressure especially when looking at whole house overall performance. Depending on the size of the house and how many and the types of outlet are used within the property will determine on how the pipe runs need to be designed and what size the pipes actually need to be.

It is quite a technical excercise to get the design right, not what a lot do and just fit and hope for the best. Basically it comes down to whether the customer is happy or not but if they've never seen how good it can actually be, then they don't know what they're missing.

Perfect example was one re-pipe I did at the tail end of last year. Mains stop tested @ 2.5bar @ 18L/Min on a 25mm MDPE supply but at the street it was confirmed as 3.5bar @ 26L/Min so we knew there was headroom there to optimise.

3 bed/3 bath (2 en suite) semi in glasgow circa 1980's with a system boiler and unvented HW. Lousy pressure and flow (average 1.5 bar with 10L/Min dynamic) anywhere except the kitchen and utility (2bar @14L/Min). The customers reason for wanting it looked at was down to the showers not being able to cope being run at the same time without significant impact to each other. All pipe work was found to be 15mm 1m after the main stop tap on a 25mm supply except the feed to UV which was 22mm but then the distribution from the unvented dropped to 15mm 1m after the cylinder (absolutely criminal IMO) .

Increased the mains to 32mm and replaced 75% of the distribution pipework to 22mm until the last branch to each outlet. Bends were kept to large radius' and removed 18 elbows and tees with better planning. All flexi's removed and outlets hard piped where possible, stop tap and ISO's changed to full bore. All free flow outlets subsequently increased to an average of >2bar @ around 20L/Min flow dynamic, all showers changed to bristan bar showers and all 3 will now run well at the same time - customer couldn't believe the difference or the reduction in water noise.

 

[xdrive]

I've ended up with 25mm pipe but will use 22mm for distribution and then tee off with 15mm. Isolation valves will be full bore. Hope it works out ok.

 

[xdrive]

I was faced with this last sept.

In the end 25mm was put in and no issues. We used a Thames WATER approved contractor who said i can put in 32mm if i want but will not make a difference if your internal pipes are 15mm. We have 25mm mdpe, then about 1.5m of 22m copper then a 15mm t junction for the rest of teh house.

How many showers? Is the flow good?

 

[xdrive]

Whilst I'm doing it would you T off blue pipe for outside garden tap?

 

[Madrab]

Whilst I'm doing it would you T off blue pipe for outside garden tap?

Nope ... ideal is control all the outlets by one main full bore 1/4 turn lever valve. Even then tho the would be another isolation/service valve and a dbl check valve/drain off before the tap.

 

[Madrab]

Oh don't get me wrong, there will be a definite benefit going to 25mm as long as the mains is good, especially if you carry 22mm up and out as the main distribution pipe size.