Gas pipe sizing

Zandoni

ComicGeek said:

Zandoni said:

The video doesn’t just just discuss the difference between old and new gas valves, it’s point is that you can’t tell by testing the old boiler. I have just had three quotes for a new boiler and all of them said they will test at the end to see if my gas pipe would need upgrading. 

In my case it’s certainly not easy to do any calculations because my gas supply is in barrel which is buried in the floor. Luckily for me mine was OK and that saved a lot of upheaval.

But testing the old boiler tells you nothing about the pressure losses in the pipework between the meter and boiler. The company fails to state that the more onerous requirement is to achieve a maximum pressure drop of 1 mbar from meter to boiler - it doesn't matter if the lowest working pressure of the boiler is 16/17 mbar, it still needs to achieve the maximum 1 mbar drop.

But what if the better answer is to install a slightly smaller boiler (with lower gas flow rate) rather than digging up your floor and replacing the pipework? Bit late if the larger boiler is already installed.

I still think it's ridiculous not to do the calc first.

Again he saying you can’t tell by testing the old boiler, so that doesn’t come into it.

He didn’t mention a 1 mbar pressure drop but they are Gas Safe so they know the rules.

I’d imagine that they wouldn’t put in a boiler that was too big anyway.

My main point is you can’t always easily do the calculations in an existing installation, my gas pipe is buried in concrete.

ComicGeek

Zandoni said:

ComicGeek said:

Zandoni said:

The video doesn’t just just discuss the difference between old and new gas valves, it’s point is that you can’t tell by testing the old boiler. I have just had three quotes for a new boiler and all of them said they will test at the end to see if my gas pipe would need upgrading. 

In my case it’s certainly not easy to do any calculations because my gas supply is in barrel which is buried in the floor. Luckily for me mine was OK and that saved a lot of upheaval.

But testing the old boiler tells you nothing about the pressure losses in the pipework between the meter and boiler. The company fails to state that the more onerous requirement is to achieve a maximum pressure drop of 1 mbar from meter to boiler - it doesn't matter if the lowest working pressure of the boiler is 16/17 mbar, it still needs to achieve the maximum 1 mbar drop.

But what if the better answer is to install a slightly smaller boiler (with lower gas flow rate) rather than digging up your floor and replacing the pipework? Bit late if the larger boiler is already installed.

I still think it's ridiculous not to do the calc first.

Again he saying you can’t tell by testing the old boiler, so that doesn’t come into it.

He didn’t mention a 1 mbar pressure drop but they are Gas Safe so they know the rules.

I’d imagine that they wouldn’t put in a boiler that was too big anyway.

My main point is you can’t always easily do the calculations in an existing installation, my gas pipe is buried in concrete.

That's part of what I do as a job, almost on a daily basis, of course you can. 

Zandoni

ComicGeek said:

Zandoni said:

ComicGeek said:

Zandoni said:

The video doesn’t just just discuss the difference between old and new gas valves, it’s point is that you can’t tell by testing the old boiler. I have just had three quotes for a new boiler and all of them said they will test at the end to see if my gas pipe would need upgrading. 

In my case it’s certainly not easy to do any calculations because my gas supply is in barrel which is buried in the floor. Luckily for me mine was OK and that saved a lot of upheaval.

But testing the old boiler tells you nothing about the pressure losses in the pipework between the meter and boiler. The company fails to state that the more onerous requirement is to achieve a maximum pressure drop of 1 mbar from meter to boiler - it doesn't matter if the lowest working pressure of the boiler is 16/17 mbar, it still needs to achieve the maximum 1 mbar drop.

But what if the better answer is to install a slightly smaller boiler (with lower gas flow rate) rather than digging up your floor and replacing the pipework? Bit late if the larger boiler is already installed.

I still think it's ridiculous not to do the calc first.

Again he saying you can’t tell by testing the old boiler, so that doesn’t come into it.

He didn’t mention a 1 mbar pressure drop but they are Gas Safe so they know the rules.

I’d imagine that they wouldn’t put in a boiler that was too big anyway.

My main point is you can’t always easily do the calculations in an existing installation, my gas pipe is buried in concrete.

That's part of what I do as a job, almost on a daily basis, of course you can. 

How can you tell the diameter of my barrel pipe buried under the floor, where it terminates near the boiler it’s flush with the wall and converts to 15mm copper?

FreeBear

Well, gas pipe put in. 0.9m of 15mm with 4 90° elbows, and 8m of 22mm with 8 90° elbows. Installer reckons he measured a 1mb pressure drop (I didn't observe the check), and the calculations suggest it should be 1.8-2.1mb.

I think I'll wait for the first service and get a Viessmann approved engineer in and get him/her to double check things. If the install isn't up to scratch, I can chase the company and as a last resort, my credit card Co.

ThisIsWeird

FreeBear said:

Well, gas pipe put in. 0.9m of 15mm with 4 90° elbows, and 8m of 22mm with 8 90° elbows. Installer reckons he measured a 1mb pressure drop (I didn't observe the check), and the calculations suggest it should be 1.8-2.1mb.

I think I'll wait for the first service and get a Viessmann approved engineer in and get him/her to double check things. If the install isn't up to scratch, I can chase the company and as a last resort, my credit card Co.

Note down now, as verbatim as poss, the conversations you've had - that you have enquired about this, and have your concerns. Timed and dated.

alanobrien

This is not a new phenomenon. I recall many years ago British Gas proposing to use 22mm pipe from the meter to the boiler cupboard (approx 10m) when we moved from an old cast iron boiler to a 30kw condensing system boiler.   They insisted it was required  even though there was a 1 1/4" gas pipe riser in the boiler cupboard.   As someone who worked my whole life as an engineer with pumps and gas compressors I put down to an over zealous salesman when i ran some calcs myself.    Two years ago we upgraded to a 34Kw boiler and all was fine.

What makes me more sceptical is a year ago all the gas pipework in our road was relined by pushing plastic pipe through the existing metal pipe right up to the house meter.   That would have reduced the gas volume available but all continues to work fine.    I don't know if they compensated for the volume loss by increasing the line pressure ?   Its a possibility i haven't had any reason to check.  

Best option do the calcs and trust your own calcs.