MDPE 32 or 25mm?

[seb963]

Hi,

I have just had Thames Water upgrade my mains connection to a 32mm MDPE, however my plumber has run a 25mm MDPE after TW stopcock from the property boundary into the house, hence I am wondering if this would have already reduced the pressure I would have had into the house. I would have expected him to run a 32mm MDPE.
The house is now on mains pressure system (converted from gravity fed system to unvented with HW cylinder) with one bathroom, but I have the plan to add a second bathroom in the loft, and I am worried that the pressure will not be enough on the 25mm pipe. The pressure on the first floor bathroom is better than with the old gravity fed system but not exceptional.
The question is whether a 25mm is ok, or should the builder have gone for 32mm for the mains inside the house? Having paid £1100 for the TW upgrade, I want to make sure this was worth the money!

Regards

Matt

 

[muggles]

The size of pipe won't affect the pressure, only the flow rate, so upgrading it to 32mm won't appreciably change anything when running one tap upstairs. It may make a difference when running multiple outlets, however

As for what your builder should have done, that rather depends on what you contracted him to do. If you contracted him to run a 32mm pipe, he should have run a 32mm pipe. If you contracted him to run a pipe of unspecified size, he may well have used up the rest of a roll he had over from another job, which in this case happened to be 25mm

I'd have run 32mm if it was me, but that's maybe the difference between using a builder and a plumber to do your plumbing!

 

[Roger928]

I ran 32mm from the main for 100m to the back off a garage on a job. Then T for the garage, reducer and 25mm for 15m into a 6 bed property. Then prv taking 7 bar down to 3.5 bar.
Never been a problem. When I tested 3 showers they all ran back to back easily.
All depends on the driving force.

 

[fezster]

Hi,

I have just had Thames Water upgrade my mains connection to a 32mm MDPE, however my plumber has run a 25mm MDPE after TW stopcock from the property boundary into the house,

As said above already, it is the flow rate which will be affected, so running multiple showers (for example) could lead to reduced flow (whether it's noticeable or not depends on how much water the outlets use). 32mm will be better than 25mm, but how much difference it makes depends on the length of the run. Also, what does the 25mm MDPE then go on to connect to?

If the 25mm MDPE is a few metres and then connects to 22mm (or less) internal pipework, this will have significantly less impact than if the 25mm MDPE is 100m in length, or connects to 28mm internal pipework.

 

[seb963]

The 25mm MDPE runs for about 5 metres and is connected to 22mm internal pipework after the internal stop cock. So, from fezster comments, I take it the 32mm MDPE would not have made a huge difference?

 

[fezster]

The pressure on the first floor bathroom is better than with the old gravity fed system but not exceptional.

Did your installer measure your static and dynamic pressure? Remember that for every 1m you go up in height, you lose 0.1 bar of pressure. Btw, the 25mm MDPE will not have any impact on this whatsoever.

Just to give you my own experience. I have a 32mm incoming MDPE able to deliver >50 l/min. Originally, this was reduced to 25mm MDPE and 22mm internal pipework. I was seeing poor performance when running 2 or more showers (each shower capable of around 20 l/min). I replaced this with 32mm MDPE to 28mm internal pipework (eventually reducing to 22mm). In particular, I believe my Megaflo 22mm PRV was causing a massive restriction in flow.

 

[seb963]

No they did not measure the pressure. I assume I can do this by myself using a water pressure gauge? Static would be with no taps open, and dynamic with at least one tap opened? what is a "standard" reading for static and dynamic pressure?
The current flow at the garden tap is about 20L/min

 

[fezster]

Take the reading from a tap before the PRV. Static with no water being drawn, and then dynamic with water being drawn at varying flow rates. Someone more knowledgeable than me can tell you what the recommended readings are. Most literature I've read states a minimum of 1.5 bar dynamic at the required flow rate.

Also keep in mind that the pressure can vary throughout the day and night.

To measure the incoming flow more accurately, use multiple taps simultaneously.

 

[Roger928]

You'll need a minimum of 1 bar at the kitchen sink with the garden tap flowing 20L/min.

 

[Dan Robinson]

You'll need a minimum of 1 bar static at the kitchen sink with the garden tap flowing 20L/min.

Static pressure under flow conditions? How does that work?

 

[Roger928]

Your right of course. I worded that wrong. I'll correct it.