New Plumbing and Heating system advice.

[TheCableGuy]

Dear Members,

I would really appreciate any advice you can give on this matter.

I am having a new central heating system fitted along with a new combination boiler to a 3 story house. Everything (pipework) is being replaced with new.

I am an electrician and have been around many plumbers and have a working knowledge of systems, but not a recent knowledge (new reg's etc for the last 10 years).

It was always my understanding (whether good practice or otherwise), that rising 'main' pipes are in at least 22mm and then radiators are fed off in 15mm.

The plumber has from the 1st floor used 22mm pipe, but has then risen to the 2nd floor in only 15mm and is feeding 2 radiators. I questioned this but he assured me that you can run 3 radiators off a 15mm.

Is this allowed when you include a rising main?

Is it even good practice when you are fitting a new installation?

I know it is a pressurised system, but surely the top of the house is under the least pressure and at risk of flow restriction?

Also we are fitting a combination boiler from the ground floor kitchen and feeding a bathroom on the 1st and 2nd floor with an en-suite also on the 1st floor. However, again I noticed yesterday the he has run all pipes from the boiler in 15mm.

Again I have questioned this for reasons of restricting flow as it need to feed 3 bathrooms. One will have a Shower fed from the combination boiler and 2 will have a separate cold feed to 2 electric showers I will be fitting.

This cannot be correct to run the entire feed from the boiler in 15mm?

The answer I received was that the boiler (Worcester Bosch) has a 15mm fitting, so it only feeds the house from a 15mm port.

I was of the impression that even of this was the case the boiler is pressurised and still needs to benefit from a higher flow rate given by a larger run such as 22mm pipes. That means that the house is reliant on 15mm pipe-works, is this correct?

Thanks in advance for taking the time to read this feel free to 'put me straight' if I have assumed something which, is not the case.

🙂

 

[GQuigley67]

the hot water pipe from combis is always 15mm, the 15mm feeding your 3 radiators will be fine.

your main cold water will be feeding everything now, so you would probably be better having your cold pipes 22mm branching off 15mm.

and you would of been better with a system boiler and unvented cylinder probably rather than a combi imho

 

[AWheating]

15 mm is correct for the hot pipework, anything bigger will just waste money/water. The cold could of maybe benifited being 22mm but that would depend on the cold supply into your hose and how the boiler is piped up. For example if the cold main has a low flow rate and you pipe cold fixtures in 22mm then you could end up starving the hot supply from the combi, so it all depends on what you have, if you went with 22mm cold pipes branching to 15mm then you will need to ensure that the combi is the very first connection after the stop tap to help hot water flow rates.

15mm can supply 3 rads depending on there size, although longer runs of 15mm will increase noise, make sure your heating is balanced correctly and it should be fine.

 

[GasmanxxxR1]

Everything your plumber has done sounds good tom me. Its how i would have done it. Yes 15mm should be enough for up to three rads

 

[stevetheplumber]

completly normal to run the top to on 15mm

 

[shorticus]

I'd agree with all said above but would add that the performance of your topfloor bathroom maybe compromised if you don't have good supply pressure specifically dynamic i.e. if you still get a decent supply when someone fushes the downstairs loo. Combi's really aren't the best solution to a three bathroom house and to have any chance you really need to have a high rate model, which Worcester have you got?

 

[Gray0689]

Should of gone standard boiler unvented cylinder combis not good for this many bathrooms IMHO

 

[ecowarm]

combi and 3 bathrooms??????????????????????????????????????????????????????????

 

[TheCableGuy]

I'd agree with all said above but would add that the performance of your topfloor bathroom maybe compromised if you don't have good supply pressure specifically dynamic i.e. if you still get a decent supply when someone fushes the downstairs loo. Combi's really aren't the best solution to a three bathroom house and to have any chance you really need to have a high rate model, which Worcester have you got?

Thanks for everybody's input here.

Hi, Shorticus

The proposed boiler is a Worcester Greenstar 42CDi.

I know 3 bathrooms sound a lot for a combi, however 1 is an en-suite and will only make use of hot water for a hand basin as I am installing an electric shower.

1 bathroom is a dedicated shower room and is on the 1st floor above the boiler, with a thermostatic valve to allow for variance from starvation that I am familiar with using combi's in the past.

The top floor bathroom is a normal bath with an electric shower fitted, again to save taxing the combi.

As we are having a loft conversion we have no place for tanks and cylinders if we want to make the most of space, so thought this was a good option.

Pressure is good, so I will have the cold increased and plumbed as you advise as good cold feeds up and around the house seem to have a high importance with the 2 electric showers.

I thought the boiler was up to the job, but feel free to comment.

Thanks again.

 

[GQuigley67]

because everything is fed off of the mains now, you would be hoping for alot of pressure and flow rate to cope, so if you have your cold properly sized to suit then you should get the most from your combi i.e having a big sized pipe coming into the house and branching off in 15mm to each individual outlet.

 

[shorticus]

Thanks for everybody's input here.

Hi, Shorticus

The proposed boiler is a Worcester Greenstar 42CDi.

I know 3 bathrooms sound a lot for a combi, however 1 is an en-suite and will only make use of hot water for a hand basin as I am installing an electric shower.

1 bathroom is a dedicated shower room and is on the 1st floor above the boiler, with a thermostatic valve to allow for variance from starvation that I am familiar with using combi's in the past.

The top floor bathroom is a normal bath with an electric shower fitted, again to save taxing the combi.

As we are having a loft conversion we have no place for tanks and cylinders if we want to make the most of space, so thought this was a good option.

Pressure is good, so I will have the cold increased and plumbed as you advise as good cold feeds up and around the house seem to have a high importance with the 2 electric showers.

I thought the boiler was up to the job, but feel free to comment.

Thanks again.

as is often the case with these things one has to sometimes make compromises, the 42cdi should give you around 17-18 litres a minute with a 35 degree temperature rise. This should be fine in the warmer months when the supply is around 10+ degrees but you may find it takes a little longer to fill a bath in winter when the supply drops to 5 or 6 degrees and the one shower that you've got from it also might not perform at it's optimum. If you've lost your storage space then you're limited in options but at least you've chosen a boiler with a decent output.
All the best
Shorty