Flow rates with this combination of pipes/equipment

[MrGatch]

At the moment I have a very old 15mm copper water supply entering through a wall in the cellar. This services a 15mm network of cold water and a combi boiler (Worcester 37kW) on 15mm copper throughout.

The house is over 4 floors with a lot of outlets. 5 toilets, 4 showers, 2 baths. Family of 4.

Don't have any major general flow problems, even on the top floor. I measured the pressure at the highest shower and it was about 2 Bar. Flow rate is acceptable (not measured it), unless another tap is opened in which case the flow drops to a dribble.

I'm having a new water main fitted. Standard 25mm MDPE pipe entering in a brand new ground floor location, directly off the main in the street.

Converting the combi setup to a system boiler with 250L megaflow (Super Oso) with a balanced supply. Proposing to run 22mm polypipe from the stopcock directly to the cylinder and a balancing valve. Then proposing to run 22mm polypipe after the cylinder (tee'ing off in 15mm a few times) until it connects with existing 15mm pipework (as it goes upstairs).

I'm paranoid about flow rate with the new setup and am hoping that you guys can tell me I don't need to worry!

I just want to ensure that a few taps can be opened simultaneously and that the bath fills up at a good rate.

If I make an assumption that the source pressure will be 3.5 Bar and flow is good then would an ageing 15mm copper network deliver fast flow-rate water from the megaflow and from the new main?

Am I wise to run some of it in 22mm?

Do I need to enquire about 32mm rather than 25mm MDPE?

Thanks in advance!

 

[ShaunCorbs]

22mm copper to the unvented system which needs to be installed by someone qualified

22mm plastic ends up being like 15mm copper (internally)

 

[Riley]

As I think has been mentioned before look at a secondary return on the hot water to ensure swift hot water delivery

 

[rpm]

At the moment I have a very old 15mm copper water supply entering through a wall in the cellar. This services a 15mm network of cold water and a combi boiler (Worcester 37kW) on 15mm copper throughout.

The house is over 4 floors with a lot of outlets. 5 toilets, 4 showers, 2 baths. Family of 4.

Don't have any major general flow problems, even on the top floor. I measured the pressure at the highest shower and it was about 2 Bar. Flow rate is acceptable (not measured it), unless another tap is opened in which case the flow drops to a dribble.

I'm having a new water main fitted. Standard 25mm MDPE pipe entering in a brand new ground floor location, directly off the main in the street.

Converting the combi setup to a system boiler with 250L megaflow (Super Oso) with a balanced supply. Proposing to run 22mm polypipe from the stopcock directly to the cylinder and a balancing valve. Then proposing to run 22mm polypipe after the cylinder (tee'ing off in 15mm a few times) until it connects with existing 15mm pipework (as it goes upstairs).

I'm paranoid about flow rate with the new setup and am hoping that you guys can tell me I don't need to worry!

I just want to ensure that a few taps can be opened simultaneously and that the bath fills up at a good rate.

If I make an assumption that the source pressure will be 3.5 Bar and flow is good then would an ageing 15mm copper network deliver fast flow-rate water from the megaflow and from the new main?

Am I wise to run some of it in 22mm?

Do I need to enquire about 32mm rather than 25mm MDPE?

Thanks in advance!

Assume nothing.

 

[Riley]

And as I also said before speak with the water company as they will be able to give you indicative flow/pressure figures to allow you to plan accordingly. I do find this all a bit suspect that you do not have an engineer in designing all this for you in what could be a pitfall laden project water wise

 

[MrGatch]

22mm copper to the unvented system which needs to be installed by someone qualified

Good advice on the 22mm copper from stopcock to cylinder.

As I think has been mentioned before look at a secondary return on the hot water to ensure swift hot water delivery

I can't run a secondary return as I don't have access to any of the pipework above ground floor level.

Assume nothing.

I have to make a few assumptions as the water supply is being completely replaced. I'm fairly sure about the pressure being acceptable for the megaflow - its more the flow rate I want to maximise.

And as I also said before speak with the water company as they will be able to give you indicative flow/pressure figures to allow you to plan accordingly. I do find this all a bit suspect that you do not have an engineer in designing all this for you in what could be a pitfall laden project water wise

I called the water company a few days ago and they guarantee 1.5 Bar and flow of 15-20 L/min. They couldn't provide specific details on my street but did say that where I live in South Manchester would generally have very good pressure and flow and that it would be adequate for a unvented cylinder. I'm getting 2-3 Bar now.


Do you guys think I will notice a considerable difference between the old and new setups I've described?

I've read so much stuff on the internet that recommends 32mm MDPE or higher and it sounds unnecessary to me, but I do have the option to do it in 32mm with extra cost and faff if there will be considerable benefit.

 

[ShaunCorbs]

Most places have 25mm alk so what I would do is get the main installed and then test your flow rates at your new stop tap

 

[CHRISX]

Hello MrGatch,

As Member Shaun has stated the `Standard` pipe size for a new Mains Water Supply from most Water Suppliers is 25mm.

I would recommend having a 32mm diameter Main installed - this should give about 28% extra Supply Volume over the 25mm diameter pipe.

We cannot tell You on this Forum how your Mains water supply`s to various outlets on various Floors will or will not be affected by other outlets being opened - however I would definitely get the 32mm Mains pipe installed - it gives You a better chance of being able to use more than one or two Mains water outlets at the same time as some Hot Water outlets.

To try and ensure that there is very good Volume available at each Floor You would have to install a new `Rising Main` throughout the House - starting in 35mm pipe and gradually reducing as the pipe goes up - 35mm - 28mm - 22mm - that will add to the expense but just having an Incoming 32mm Mains pipe supplying the existing Rising Main pipe would not be advisable.

IF there is still a problem after having the 32mm Mains installed and upgrading the Rising Main pipework it would have been worse with a 25mm Incoming Mains pipe.

Regards,

Chris

 

[Riley]

I think as Chris brilliantly alludes to, I really think if you want top performance from your system that you should not rely on the builder. It just sounds like you are doing so much research on this matter that you really want to do it properly, with results your family can all enjoy. I fear that the avenue you are heading down is going to lead to unsatisfactory results and you left with a bad taste in your mouth after parting with your hard earned cash. I really implore you to get a second opinion on your plumbing design

 

[justlead1]

When you increase the pipe size on hot supply, it also increases the volume of system. Which means you will need to pull more cold water off before hot water occurs at tap/shower.(high water bills)
If you do not increase the pipe size on the hot you won't achieve much. So your between rock and hard place. From the new cylinder installation run a 22 mm up through the building and tee off at each floor, whilst doing that run a 15 mm secondary return from the highest point leg and back to cylinder ( if there are no long horizontal runs it may well work on gravity, saving the bronze pump costs)
It is also worth remembering that when comparing sizes of pipe, it done on Sq area.
Eg. 15 mm pipe 176 mm Sq
22 mm pipe 380 mm Sq
28 mm pipe 615 mm Sq
32 mm pipe 804 mm Sq
You can see a 22 mm pipe is more than double to that of a 15 mm pipe etc etc etc.
You will always be limited when working of mains supply as you have no control over available supply.
When the use of CWSC (cold water storage cisterns) were employed. One had a constant to work with, albeit low pressure the pipes could be sized according to the flow rates required. As the storage in houses reduces over time ( the installation of direct main systems, combi, unvented etc) draw lots of water from main system, which were not designed to provide such a demand. That is why you can expect lower provision during high demand times.