Gas pressure at boiler

srcandas

Is there any practical way to have measured the gas pressure/flow at the input to a boiler?

Thus meaning you can choose a replacement boiler which will work?

:beer:

booty40uk

The gas Working pressure at the meter should be 21mbar +\- 2mbar . ie 19 to 23mbar. There should be no more than a 1mbar drop between the meter and the appliance through the pipe work. So at the appliance you should have a minimum of 18mbar working pressure. In an ideal world you will have 20mbar.

It is a simple task to check this but you will need an RGI'S to do it.

srcandas

booty40uk wrote: »

It is a simple task to check this but you will need an RGI'S to do it.

Booty tx but if it is simple why doesn't an RGI do it and not guess??

From RGIs had views from "yes no trouble, that will work", through to "not a chance guv but we can rip your house apart putting new pipes in"

The pipe is 22mm from gas meter, then under solid floor to where it appears as 15mm into the boiler. Logically the 22mm to 15mm occurs 2 meters before the boiler where a supply for a gas cooker Ts off (no gas cooker but I've seen the sealed off pipe).

There must be a method better than flipping a coin

Gloomendoom

I have the same problem. My old inefficient boiler gets enough gas to heats the house adequately using a 15mm pipe, yet I have been told that a modern, much more efficient, replacement boiler will require a 22mm feed, even though it needs less gas to generate the same amount of heat.

unclebulgaria

There is an easier way by using a formula that takes into account the resistance in the piping supplying the gas to the appliance. Copper and Steel have different resistances and how many elbows, bends and distance will determine the size of the pipe to supply your boiler. I can guess quite accurately whether a pipe will suffice but usually do the math to confirm it.
Modern boilers are more efficient but that doesn't mean they use less gas when operating, just use it more efficiently.
Manufacturers also specify what pipe size is required as minimum.

Gloomendoom

unclebulgaria wrote: »

Modern boilers are more efficient but that doesn't mean they use less gas when operating, just use it more efficiently.

I'm baffled.

I'm no physicist, but doesn't the first law of thermodynamics apply to modern gas boilers?

booty40uk

I am assuming you are looking to have anew combi installed?

The manufacturers instructions for all boilers will specify the size of pipe required to feed their boiler. This is the size of pipe that must therefore be used. Any deviation from manufacturers instructions and they would more than likely not honour any warranty.

As far as I am aware, all modern condensing combination boilers require a 22mm connection to the boiler. At least the models I fit do.

I don't totally disagree that 15mm may be ok to obtain the correct flow and pressure but as an rgi I would install as per MI's to cover myself and possibly the customer in case of a future warranty call out.

Hope that makes sense.

srcandas

booty40uk wrote: »

Hope that makes sense.

Booty and UncleB that makes sense -- in a sense

But are the boiler requirements saying it needs a 22mm connection with a certain flow/pressure. Or are they saying that the pipe must be 22mm from source to boiler?

And in my case I could simply replace the last two meters of 15mm with 2 meters of 22mm (not too much digging :cool:) and this would meet the need. But would it?

One can make assumptions as to the route of the pipe below ground and thus apply the algorithm but one cannot be 100% sure.

Gloomanddoom glad to know I am not alone :beer:

And having been assured it is ok and having been assured it isn't where does that leave me :rotfl:

Gloomendoom

booty40uk wrote: »

I am assuming you are looking to have anew combi installed
As far as I am aware, all modern condensing combination boilers require a 22mm connection to the boiler. At least the models I fit do.

Actually, no, I specifically don't want a combi. Can you recommend a non-combi boiler that can be used with a 15mm feed, assuming it meets the minimum pressure and flow requirements.

keystone

I'm guessing that you have had a quote (more than one?) to replace the existing and they all suggest that the gas supply pipework needs upgrading. You are trying to avoid that?

Its the flow that matters. Modern boilers almost invariably need a higher flow rate than older ones and thats dependent on pipe size for a given pressure. So the pipe needs upgrading to 22mm from 15mm from the meter all the way to the boiler. It's not a whim of the installer it will be in the MIs and shouldn't be ignored.

Sorry but its a fact of life.

Cheers

srcandas

keystone wrote: »

I'm guessing that you have had a quote (more than one?) to replace the existing and they all suggest that the gas supply pipework needs upgrading. You are trying to avoid that?

You are miss-reading if this relates to me. I have quotes from qualified RGIs which say:

The pipes DO need replacing
The pipes DO NOT need upgrading
The pipes may in part need upgrading

No one is trying to avoid anything. Just looking for honest answers no matter what cost that may lead to.

keystone wrote: »

Its the flow that matters. Modern boilers almost invariably need a higher flow rate than older ones and thats dependent on pipe size for a given pressure. So the pipe needs upgrading to 22mm from 15mm from the meter all the way to the boiler. It's not a whim of the installer it will be in the MIs and shouldn't be ignored.

Sorry but its a fact of life.

It maybe a fact of life but when changing a boiler there seem to be many conflicting facts of life. Each RGI I have met seems determined that they are right

I image I am in a similar position to many one or two people households in small houses. A combi is very attractive but costs and inconvenience escalate along with the range of solutions - each promised to be perfect for conflicting reasons.

But we will get there :beer: