3/8 or 1/2 gas pipe

[Poppin]

I have a very short run from gas bottles to oven and hob, which will be the only appliance on my boat. The run is about 2 meters. I feel that 3/8 pipe is adequate for this, am I wrong? People advise me to use 1/2, just in case. However the thinner pipe I already have, it can be bent by hand, can fit around awkward places and I also believe will go with a bubble tester without needing to make a bypass. Any thoughts welcome! 

[rusty69]

I suspect you may need to give further details about the oven and hob KWh to get any meaningful answers.

 

You could use 1/2 for the main run and tee off with 3/8.

[MtB]

1 minute ago, rusty69 said:

I suspect you may need to give further details about the oven and hob KWh to get any meaningful answers.

 

You could use 1/2 for the main run and tee off with 3/8.

 

 

The OP also needs to state what regulation(s) s/he wants to meet. 

 

If just BSS then 3/8 is fine. If RCR then it probably needs to be 1/2" but as you say, we would need to know the combined heat input of the two appliances.

 

Input, not output. 

[Poppin]

I have not decided on an oven but there are few full sized that are completely gas including the grill. Will probably go for the hotpoint SHY23X. Hob will be any 4 ring hob. 

 

The other issue I have is that the boat builder has made the outlet hole in the gas locker rather large with a 3/4" female thread. As far as I can tell there are no bulkhead gas fittings for this? 

[Tracy D'arth]

2 minutes ago, Poppin said:

I have not decided on an oven but there are few full sized that are completely gas including the grill. Will probably go for the hotpoint SHY23X. Hob will be any 4 ring hob. 

 

The other issue I have is that the boat builder has made the outlet hole in the gas locker rather large with a 3/4" female thread. As far as I can tell there are no bulkhead gas fittings for this? 

3/4" Brass bush the hole and fit a bulkhead fitting with no centre stop so that the pipe goes through uncut.

[rusty69]

Just now, Tracy D'arth said:

3/4" Brass bush the hole and fit a bulkhead fitting with no centre stop so that the pipe goes through uncut.

Yes. I did that. Not sure how legal it is though. 

[Poppin]

11 minutes ago, Tracy D'arth said:

3/4" Brass bush the hole and fit a bulkhead fitting with no centre stop so that the pipe goes through uncut.

Do these exist? Would I need to drill the fitting?! 

[Tracy D'arth]

7 minutes ago, Poppin said:

Do these exist? Would I need to drill the fitting?! 

I just file them out with a rat tail file, the stop is small and not very wide, takes a couple of minutes but eliminates 2 joints, less to leak. Technically they are a slip coupling then. You may find that the 1/2" pipe bulkhead does fit a 3/4" threaded hole, it will be about 19mm clearance.

[Alan de Enfield]

43 minutes ago, Poppin said:

I have a very short run from gas bottles to oven and hob, which will be the only appliance on my boat. The run is about 2 meters. I feel that 3/8 pipe is adequate for this, am I wrong? People advise me to use 1/2, just in case. However the thinner pipe I already have, it can be bent by hand, can fit around awkward places and I also believe will go with a bubble tester without needing to make a bypass. Any thoughts welcome! 

 

 

Well you can either guess or you can use what is detailed in the ISO specifications for small boats (don't forget to allow for bends and joints equivalence) :

 

 

 

 

[Tracy D'arth]

12 minutes ago, Alan de Enfield said:

 

 

Well you can either guess or you can use what is detailed in the ISO specifications for small boats (don't forget to allow for bends and joints equivalence) :

 

 

 

 

This table is erroneous, it makes no consideration  for the wall thickness of the pipe which has changed over the years for commonly available soft drawn copper pipe.

This has come up before on this forum.

[MtB]

52 minutes ago, Tracy D'arth said:

This table is erroneous, it makes no consideration  for the wall thickness of the pipe which has changed over the years for commonly available soft drawn copper pipe.

This has come up before on this forum.

 

Nobody cares. Nobody checks. Use what you like!

 

 

 

[Alan de Enfield]

1 hour ago, Tracy D'arth said:

This table is erroneous, it makes no consideration  for the wall thickness of the pipe which has changed over the years for commonly available soft drawn copper pipe.

This has come up before on this forum.

 

 

 

I'm not quite sure how the wall thickness affects the pressure drop per metre, does it ?

 

Yes the wall thickness has changed over the years and the specification stipulates what wall thickness is acceptable :

 

6.2 Piping

6.2.1 Only solid drawn copper or drawn stainless steel piping, which are galvanically compatible, shall be used for rigid supply lines. Wall thickness for piping shall be greater than 0,8 mm for piping up to 12 mm outside diameter and a minimum of 1,5 mm for an outside diameter greater than 12 mm.

 

6.2.2 There shall be no joints or fittings in piping passing through engine compartments.

 

 

This shows why it is important to read the whole specification.

 

You can even have the complete system made with rubber hoses (as per one of my boats that was built in France) No metallic piping used or needed and the specification is covered in the BSS guidance.

Edited May 19, 2023 by Alan de Enfield

[MtB]

1 minute ago, Alan de Enfield said:

This shows why it is important to read the whole specification.

 

Only if the OP wishes to comply with the specification. 

 

And so far, they haven't mentioned what they want to comply with, so it's a moot point. 

 

 

 

[Alan de Enfield]

Just now, MtB said:

 

Only if the OP wishes to comply with the specification. 

 

And so far, they haven't mentioned what they want to comply with, so it's a moot point. 

 

 

 

 

I was responding to Tracy who suggested that the wall thickness of the pipe was not covered by the 'table'.

[MtB]

2 minutes ago, Alan de Enfield said:

 

I was responding to Tracy who suggested that the wall thickness of the pipe was not covered by the 'table'.

 

And I am pointing out the table may be irrelevant. Unless the OP tells us what regs he wants/needs to comply with. 

[blackrose]

On 19/05/2023 at 23:11, MtB said:

 

Nobody cares. Nobody checks. Use what you like!

 

 

Surely even the most basic BSS inspection will check that all burners on a hob and oven can all be lit at the same time and burn correctly? If the main pipe run is too restrictive they won't.

 

I used some Calor tables 17 years ago to size my main pipe run diameters according to kW output of the appliances and the length of run. They were available online back then but I can't find them anymore.

[BEngo]

1 hour ago, blackrose said:

 

Surely even the most basic BSS inspection will check that all burners on a hob and oven can all be lit at the same time and burn correctly? If the main pipe run is too restrictive they won't.

The BSS looks at this, but it is a non sense check.  The burners are designed so their heat output is controlled by varying the gas pressure to the burner jet,  using the control knob or oven thermostat. The burner itself will, by its design, burn cleanly across the range of pressures the control knob/thermostat delivers. It may produce extra CO at some settings, but the  BSS check cannot look for this. It is also wory remarking that a typical ribbon burner found in gas ovens will burn with a yellow tipped flame.  This is the case regardless of the inlet pressure, within the design operating range.

 

  It follows that if the system gas pressure at the cooker inlet is low because the pipe is undersized (or the regulator is  duff)  the burners will still burn cleanly. It may take longer to fry your egg though.

 

N

 

Edited May 21, 2023 by BEngo