15mm or 22m for correct gas pressure

[John D v2.0]

How many elbows you going to have on a 1 metre run!!!!

Don't ask me i haven't seen the photos,

 

[Gasguru]

Plenty of 60Kw boilers in domestic properties, and plenty of 50mm gas pipe in larger domestic properties.

What boiler manuals say is irrelevant...they often say 22mm to try and prevent the complete idiots installing on 15mm. In reality 22mm is often insufficient but when you're dealing with muppet installers.

Gas regs state a maximum of 1 mbar drop from meter to appliance inlets.

I would inspect exisiting piperun...and if looked marginal (maybe even calc. the drop) I would leave it as something to be addressed at commissioning stage..ie. upgrade if necessary when the drop can be meausred.

Undersized gas pipework is not an option...it MUST be correct.

 

[bernardgreen]

Nissan luxury Coupe

A gas guzzler, use largest pipes......

 

[durhamplumber]

Plenty of 60Kw boilers in domestic properties, and plenty of 50mm gas pipe in larger domestic properties.

Oh well...another school day.I stand corrected.

 

[Dan Robinson]

Oh well...another school day.I stand corrected.

Been a school week for you really .

Here's 2 we did a couple of years ago:

Prefer to do multiple boilers now though where there's space:

 

[fixitflav]

had a couple of quotes for replacing an existing vented CH System S plan, going to pressurised system (not hot water ) either WB or Vaillent. 15kw. (system boiler or heat only.

last quote said that 15mm gas feed is OK so long as there is 16.5 operating pressure, is that correct figure please? no other gas appliances in the property (flat).
thanks

Out of curiosity, do you mean the new boiler won't be used for DHW?

Not that it affects the gas pipe size. For 15kW the gas flow will be 1.6m3/h tops. According to my calcs, for 15mm (13.6mm ID) pipe x 8m length with 4 off 90° bends, the pressure drop is 0.9mbar. You or your fitter should of course check, but if you agree and your system is something like that, 15mm pipe is OK.

 

[muggles]

Thanks for replies, I suppose that I just assumed that there has to be 16.5 coming out of the gas pipe into the boiler but looks like not so simple. I know a bit about CH systems but nothing about gas pressure, I don't really want to pay for increasing the pipe size to 22mm unless I have to. I thought that 15kw is one of the smaller boilers so not so much gas required?

The gas pressure at the appliance is affected by three things - diameter of pipe, length of pipe, and number of changes in direction. 16.5mBar is acceptable at the appliance only when 17.5mbar or less is being produced by the meter, as the maximum permissible difference between the two is 1 mBar. In reality though, gas suppliers are supposed to provide a minimum of 19mBar at tbe meter, so your existing pipe run may actually already be undersized for your existing boiler

 

[gasbusters]

Thanks for replies, I suppose that I just assumed that there has to be 16.5 coming out of the gas pipe into the boiler but looks like not so simple. I know a bit about CH systems but nothing about gas pressure, I don't really want to pay for increasing the pipe size to 22mm unless I have to. I thought that 15kw is one of the smaller boilers so not so much gas required?

The installer would have to calculate the pipe sizes accordingly and then decide which size is needed. Theres no guess work involved its all calculated via pipe sizing calcs. He would need to take into account the number of pipe bends and pipe fittings along the pipe runs as these all affect the pressure.

As others have stated there is only a 1mb pressure drop allowed between meter and appliance. Any larger drop would mean the pipe is incorrectly sized.

 

[rhinosaw]

thanks for your comments
fixitflav , sorry I wsn't clear, using old copper hot water cylinder indirect

The meter is in a cupboard outside the front door, 28mm going in and out of the meter then the pipe goes into a concrete floor to the kitchen where it must split, there is a 22mm connection coming out of the wall (not used) at the other end of the kitchen to the boiler (15mm connection)

 

[fixitflav]

16.5mBar is acceptable at the appliance only when 17.5mbar or less is being produced by the meter

But 17.5mbar at the meter would be a fault anyway. If that's the case the problem is supply pressure into the meter, or the meter characteristics (most likely the former) and the gas company should be informed.

The previous quote said 15mm gas feed is OK so long as there is 16.5 operating pressure (which is almost certainly true in practice). He didn't say that 16.5mbar is the pressure, the way I read it.

 

[fixitflav]

thanks for your comments
fixitflav , sorry I wsn't clear, using old copper hot water cylinder indirect

The meter is in a cupboard outside the front door, 28mm going in and out of the meter then the pipe goes into a concrete floor to the kitchen where it must split, there is a 22mm connection coming out of the wall (not used) at the other end of the kitchen to the boiler (15mm connection)

You haven't given any lengths, but if the disused 22mm connection is after the buried section, that part is unlikely to be smaller, might even be 28mm. Presumably replacing the buried part is your main concern, so on that basis upping it is unlikely to be needed. But losses need checking.

 

[Dan Robinson]

The previous quote said 15mm gas feed is OK so long as there is 16.5 operating pressure

Operating pressure taken from where?

 

[muggles]

But 17.5mbar at the meter would be a fault anyway.

Not necessarily

 

[fixitflav]

Operating pressure taken from where?

I read it as being at the boiler inlet, but I agree it's not clear. If it's at the meter outlet it's even further outside the regs.

 

[Dan Robinson]

I'm asking you.

And define boiler inlet.