Any merit to running new dedicated 22mm water supply to combi?

[Laggy]

…from stopcock, rather than using a more convenient 15mm close by that already serves various taps and appliances.

The 15mm has a flow rate of 15l per minute without other taps and appliances running.

Boiler is a 32kw intergas rapid.

Thanks!

 

[ianmcd]

simple answer is no

 

[Madrab]

simple answer is no

The more protracted answer ....

Basic criteria around pipe sizing - a 15mm pipe will flow ~ 20L/Min @ ~2m/s. ~2m/s being the standard threshold when water velocity can start to become noisy and create more wear on pipe and fittings. If the flow exceeded that then the pipe size would increase.

 

[ianmcd]

The more protracted answer ....

Basic criteria around pipe sizing - a 15mm pipe will flow ~ 20L/Min @ ~2m/s. ~2m/s being the standard threshold when water velocity can start to become noisy and create more wear on pipe and fittings. If the flow exceeded that then the pipe size would increase.

So no

 

[Madrab]

So no

Ermmm .... Yup ...

 

[Laggy]

Hmmm, well I’ve tested the supply where I would join my 22mm pipe (right after stopcock) and it does just over 18l/m

I’ve then tested from the convenient 15mm pipe and it does 15l/m

My intergas rapid 32 does 18l/m for 25deg rise, doesn’t that mean I should go with the 22mm option?

 

[Madrab]

Not really, cold water during the winter can get down to 5degC, that would mean the HW would only be 30degC at that rate, ideally hot water at the outlet wants to be >45 degC, so the flow would drop to ~13L/Min. Though 18L/Min still keeps it within the 15mm region.

 

[JCK1]

I ran 28 mm copper from stopcock on ground floor where mdpe comes into house to just before boiler in loft, there are several 15 mm cold water take offs along the way to different sinks baths and toilets , none of take offs impact my combi shower flow or temperature. Toilets refill very fast after flush as there is very small pressure loss in system . Yes it can be called overkill but no regrets

 

[Laggy]

I ran 28 mm copper from stopcock on ground floor where mdpe comes into house to just before boiler in loft, there are several 15 mm cold water take offs along the way to different sinks baths and toilets , none of take offs impact my combi shower flow or temperature. Toilets refill very fast after flush as there is very small pressure loss in system . Yes it can be called overkill but no regrets

Thanks JCK, this was sort of the reply I expected, I don’t see how feeding a 18l/m combi with a 15mm pipe that has all other taps and appliances branched off of it is as good as a dedicated supply from stopcock like others have suggested when there is another 3 l/m available there, and when the boiler is providing DHW and another tap is opened then there is a 15mm and a 22mm supplying rather than just a 15mm..?

 

[denso13]

How difficult is it to do? If not too bad and you want peace of mind go for it. It is also a bit of future proofing for later on.

 

[Laggy]

How difficult is it to do? If not too bad and you want peace of mind go for it. It is also a bit of future proofing for later on.

Cheers for input, it’s not difficult, it’s just going to cost me an extra 200 quid to do it. I was kinda looking for confirmation that it’s worth it, I’m interested to hear why it isn’t though if that’s the case provided there’s some sense to it and it’s not just other people thinking I didn’t do it and it’s fine..

 

[vulcancontinental]

Run a tap over a measuring jug and take the time to fill it at 15/m or 18l/m or simply watch the flow at 3l/m for improvement then think £200.

I don't think it's worth it but it's not my £200. Leave it as it is and get hotter water.

 

[Laggy]

Run a tap over a measuring jug and take the time to fill it at 15/m or 18l/m or simply watch the flow at 3l/m for improvement then think £200.

I don't think it's worth it but it's not my £200. Leave it as it is and get hotter water.

Interesting, I see why the 15mm will result in hotter water, but as this combi will be feeding the shower and I want a big head on it, I thought there might be merit to it as if I run the 15mm at 15l/m then this flow will further reduce where the cold side of the mixer on the shower opens as this comes off the same 15mm further down the line. Thanks for your advice.

 

[oilhead]

The telling comment about your situation is whether you would gain any advantage and this has already been explained as your boiler will lift 18 l/m 25C, or mainly tepid. To increase delivery temperature, you will need to reduce the flow rate. I have had to explain many times that where a cylinder has been replaced with a combi, the 3/4" bath taps fed by 22mm pipes need to be turned to get a reasonable bath temperature.

 

[nitro23456]

The telling comment about your situation is whether you would gain any advantage and this has already been explained as your boiler will lift 18 l/m 25C, or mainly tepid. To increase delivery temperature, you will need to reduce the flow rate. I have had to explain many times that where a cylinder has been replaced with a combi, the 3/4" bath taps fed by 22mm pipes need to be turned to get a reasonable bath temperature.

Turned?