boiler install gas pipe size

[g35brit]

I need a new boiler and would prefer a 35KW combi boiler but wanted to know if my existing gas pipe will allow it. I wanted to check this first so i can look at my boiler options before getting somebody around.
I don't have any other gas appliances and my existing pipe is 22mm. The gas meter is located next to our front door in a box at ground level. I have no wish to take up my Oak floor to lay a new pipe.
I have attached a rough sketch of the gas pipe run and would appreciate any advise. Thanks .

 

[Scott_D]

How many elbows & tees on the gas run

 

[g35brit]

How many elbows & tees on the gas run

Seven elbows no tees as shown on the sketch I attached.

 

[SimonG]

Your gas safe engineer will take care of all that. Get them in early.

 

[Scott_D]

20m of 22mm isn’t big enough for a 35kw boiler

 

[steadyon]

1. Your gas run is roughly 20 metres.
2. You appear to have 7 elbows. I'd suggest you count this as 10 (allowing for ones by the meter which may have been missed), so a further equivalent 5 metres.
3. The manufacturer's data will tell you exactly, but a 35 kW boiler will require around 3.8 cubic metres of gas per hour.
4. A 25 metre run of 22 mm pipe will only support a flow rate of 2.6 m cubic metres / hour, so is inadequate.
5. Subject to a specific site survey, you would need 28 mm pipe for the run.
6. Because gas is compressible, a required flow rate may be achievable with a mixture of pipe sizes. This would need a precise on the spot calculation. It can't be done over the internet. However, it MIGHT allow you to avoid damaging a floor.
7. For those who might consider this too much information, all the above is freely available on the internet. Mostly at https://copperplumbing.org.uk/sites...achments/domestic-gas-planning-and-sizing.pdf

 

[ShaunCorbs]

Gut feeling 28mm required as it’s around 20m

24kw is pushing it for 20m on 22mm

 

[g35brit]

Ok thanks all. New pipe was my gut feeling but it's a real pain having to lift an oak floor and chase across a newly tiled kitchen floor.
I was looking at a 35k Worcester greenstar 8000 lifestyle as we have a Bosch Worcester floor mounted 400 high flow at the moment, the difference being the floor mounted has a hot water storage tank in it.
I have 5 bedrooms, one bathroom and one shower room and no other gas appliances so maybe a smaller KW would be ok. What do you think?

 

[Chuck]

I need a new boiler and would prefer a 35KW combi boiler but wanted to know if my existing gas pipe will allow it. I wanted to check this first so i can look at my boiler options before getting somebody around.

If you can find space for a hot water tank somewhere you could have a (much?) smaller boiler and the pipe capacity would no longer be an issue.

 

[ShaunCorbs]

I would say unvented cylinder and a boiler if you have the space

if not could you go external with the gas pipe and back in close to the boiler ?

 

[king of pipes]

Sorry to say a 35kw boiler will need a new 28mm gas supply , you would be better to fit a unvented hot water cylinder paired with a new lower kw output boiler for a family home. Kop

 

[g35brit]

I would say unvented cylinder and a boiler if you have the space

if not could you go external with the gas pipe and back in close to the boiler ?

Yes we looked at that as we can avoid going across the front of the house because the front room has carpet and suspended floor. But it would go the full length of our sideway and across the back. We have rendered walls with a black plinth along the bottom which is set back from the render 10mm so even if we tucked it under there it will stick out a fair amount, possibly 35/40mm.
Would look pretty ugly.
[automerge]1600508996[/automerge]

Sorry to say a 35kw boiler will need a new 28mm gas supply , you would be better to fit a unvented hot water cylinder paired with a new lower kw output boiler for a family home. Kop

The only place I have room for a cylinder is below the new wall hung boiler where the existing floor mounted boiler is but I'm not sure that would be enough space. I have attached a picture.
[automerge]1600510574[/automerge]
Thanks for all the advise, even though my original plan was for a smaller neater boiler perhaps I should go like for like and fit a direct replacement (greenstar 440 CDI high flow) which has a 7.5 - 29.2KW rating , I'm guessing that will work with my pipes.
Just trying to get my head around my best option before getting the engineer around . When you book an engineer through Bosch online you have to pick the boiler you want .

 

[Pathfinder]

I need a new boiler and would prefer a 35KW combi boiler but wanted to know if my existing gas pipe will allow it. I wanted to check this first so i can look at my boiler options before getting somebody around.
I don't have any other gas appliances and my existing pipe is 22mm. The gas meter is located next to our front door in a box at ground level. I have no wish to take up my Oak floor to lay a new pipe.
I have attached a rough sketch of the gas pipe run and would appreciate any advise. Thanks .

Sorry to say a 35kw boiler will need a new 28mm gas supply , you would be better to fit a unvented hot water cylinder paired with a new lower kw output boiler for a family home. Kop

I you go up the wall just inside the wall with 28mm pipe at where meter is across in ceiling to where 22mm pipe where 10meter pipe is go half way on that pipe and join with reducer you have plenty of gas for 35kw boiler.

 

[steadyon]

1. The range of the boiler is irrelevant I'm afraid. The testing must be done at full output, and your pipework will not cope with a 27 kW load.
2. As already stated, the absolute maximum your current pipework can support (subject to survey) is around 24 kW, and given the number of bends / elbows I suspect it won't really even support that.
3. If any of the long lengths on your diagram could have larger diameter pipes installed without major disruption, you might be able to upgrade those to 35 mm pipes and leave the remainder as 22. But this is a calculation which MUST be done by a Gas Safe Registered engineer who has full view of the site.

 

[Chuck]

The volume of pipework being discussed here looks to me as though a commercial installer is going to be needed.

 

[g35brit]

Is it possible for a gas Safe plumber to come around, open the gas pipe where the existing boiler is and actually take a pressure/flow reading so I know what I have exactly?

 

[Timmy D]

Is it possible for a Registered Gas Engineer to come around, open the gas pipe where the existing boiler is and actually take a pressure/flow reading so I know what I have exactly?

If the old boiler works, they can use it to get a ball park figure.

You need to measure the operating pressure.

Now saying that, I see very little benefit of the above if your diagram is correct. Pressure loses and acceptable pipe sizes can all be worked out with a calculator.

I’ve had to remove a 6 month old 30kw boiler before and replace it with a 12kw due to gas pressure issues.

The 12kw supplied a 160ish litre unvented cylinder, which in turn fed a one bed/bathroom flat. No issues with running out of hot water or heating.