Help needed for gas pipe size

[10Pints]

Hi

We are in the middle of an extensive kitchen refurbishment which included replacing an old boiler with a new Vaillant eco-tec 831 boiler in a new location. As this involved replacing most of the existing gas pipe we decided replace and hide the gas pipe in the hall way as well because it was fitted around the ceiling and was clearly visible. We also installed a new dual fuel range connected to a spur of the main gas pipe.

This work was done by a registered Gas Safe engineer and after completion I put down a new solid wood floor which has been sanded and varnished. The range cooker was bought second hand and needed to have the jets changed from LPG to Natural Gas so I thought it would be a good idea to have a qualified person do the work and check the cooker over as well so we knew it was safe.

The chap who installed the boiler and new gas main said he didn’t do cookers so I contacted a second Gas Safe engineer who after completing the work he said he couldn’t sign the cooker off because the main gas pipe was 22mm instead of 28mm and if the cooker was used the gas pressure would be too low for the boiler to operate properly which would make it dangerous.

The boiler is 31kW and the range has 5 gas burners totalling 5kW. The total distance from the meter to the boiler is 22.55m with a total of 21 elbow bends. The ‘T’ to the cooker is at 16.4m and has 2 elbows. At 1.3m before the boiler the pipe reduces to 15mm and has 3 of the 21 elbows.

I have attempted to do some calculations myself but as I’m a total amateur I don’t believe my results as they appear to be so far out and I can’t believe a Gas Safe engineer would say a 22mm gas pipe is OK.

According to my calculations even if you connected the boiler directly to the meter without the cooker or any elbow bends then 22.55m of 22mm gas pipe can supply 2.7 m³/hour and a 31kW boiler requires 2.9m³/hour!! I must be doing something wrong.

I have a diagram of the gas system which I will attempt to attach to this post together with my calculations.

View media item 48370
Please can someone double check my sums.

Many Thanks.

10Pints

[/img]

 

[xr4x4]

I don't do gas, but I sounds like to me you should have had a 28mm gas pipe installed for that long run and the big range cooker.

 

[Agile]

Exactly!

It sounds as if you have had someone who has always only used 22 mm for the last 40 years and is totally out of touch with the requirements of modern boilers and cookers and does not want to or even know how to do the calculations.

To compound your problems you have apparently covered up most of the gas pipework!

I am not sure what to suggest. If you wanted to be nasty and had all the work confirmed in writing then you could require the engineer to correct it at his cost. But then the floors and everything you have laid since are a major problem.

Wha do YOU think you should do now?

Tony

 

[gaswizzard]

Well .............total pressure drop at boiler with all appliances running would be around 4.56 mb.

5kw for a range cooker?

The 831 has a discharge rate of 3.3 m3/hr.

Pipework is wayyyyyyyyyyyy undersized , proper jobs cost ££££££££££££.

 

[gaswizzard]

Exactly!

It sounds as if you have had someone who has always only used 22 mm for the last 40 years and is totally out of touch with the requirements of modern boilers

Or maybe a crash course boiler basher/repair who hasn't a clue.

I am not sure what to suggest.

 

[ianmcd]

********

 

[swbjackson]

****

Is the oven gas as well? This can cause problems with food being undercooked when the boiler is run. A fitter that worked for the same firm as me thought he would get away without upgrading a gas pipe. Whole family went down with food poisoning due to an undercooked chicken. Someone had a prolonged shower whilst it was in the oven. You'd have thought that they would have noticed their dinner was half raw but apparently not.

 

[10Pints]

Many thanks to all of you who have replied to my post.

It has confirmed that my calculations although not exactly correct do show that a 28mm pipe should have been used and the 22mm pipe needs to be replaced what ever it may cost.

The Gas Safe fitter concerned is quite a young chap I would guess about 25 so it's not as if he is stuck in the old ways of 22mm. I'm not keen to complain to Gas Safe and potentially damage his business over what could be a simple mistake or perhaps inexperience on his part.

What to do next...

Now I have confirmation that a 28mm pipe is required I will contacted the plumber and suggest that we come to some agreement about the work to be done.

There is a way to run the new pipe without lifting the floor but it will involve a lot of work by knocking a hole through 2 walls going around the kitchen skirting boards below unit level (Ikea units with no room for services), cutting a channel in the stone/brickwork around the cooker that's in an alcove where the old victorian range used to be and removing some wooden panelling.

I don't mind doing this work and I'm even willing to pay the cost difference between 22mm & 28mm pipe and fittings but he will have to supply his labour free of charge.

Hopefully he will agree to this.

Finally many thanks to all of you guys that take the time to reply to posts. I use diynot for all trades and find it very helpful for advice on how to do a job and more importantly to know when not to do a job and get the professionals in.

After a long days graft to come home and sit in front of a computer answering questions from novice/idiots like me when you be enjoying a pint down the local is devotion above and beyond the call of duty.

Keep up the good work.

Thanks again.

10Pints

 

[gaswizzard]

What's with the guess work? , 28mm is undersized , get the job done by someone who knows what they are doing.

If you are supplying materials be in for a shock , 35mm tube and fittings aint cheap.

 

[gaswizzard]

If the first 5-6m are accesible you cold get away with up grading these to 28mm...I am not clear if the new floor is in the hall too...

Total load from meter to first branch is 3.77 m3/h.

Length from meter to first branch is 15.44 metres + 13 elbow = 22.44 metres equiv length.

22.44 x 2 branches = 44.88 metres.

3.77m3/hr at 44.88 metres requires 35mm tubing to first branch.

 

[ALEC1]

The total load to the first branch is 3.77m3, and has equivalent length of 22.44 m, on that I agree...

But whats this about doubling it for 2 branches...

 

[Terrywookfit]

The total load to the first branch is 3.77m3, and has equivalent length of 22.44 m, on that I agree...

But whats this about doubling it for 2 branches...

Got me puzzled also.

Load to first branch is 3.77m3.
28mm pipe will deliver 3.9 m3 over 40m which gives .56 mb drop. Plus any drop from there to appliances.

Or have I been wrong for 40 years

 

[gaswizzard]

The total load to the first branch is 3.77m3, and has equivalent length of 22.44 m, on that I agree...

But whats this about doubling it for 2 branches...

Each sections effective length is multiplied by the number of sections , if the OP had a gas fire added then this would be 3 sections.

 

[gaswizzard]

Load to first branch is 3.77m3.
28mm pipe will deliver 3.9 m3 over 40m which gives .56 mb drop. Plus any drop from there to appliances.

Agreed but effective length from first tee to boiler is...

4.45m of 22mm @ 3.3m3 = .29 mb loss
4.2 m of 15mm @ 3.3m3 = 2mb

I doubt the range cooker being 5kw but if correct then 28mm to first tee with 22mm tube all the way to boiler (.6mb loss) , total loss at boiler would be..

0.56mb + 0.6mb = 1.16mb.

35mm from meter to first tee = .3mb

0.3mb + 0.6mb = 0.9mb. loss at boiler , many ways to skin the cat just all depends on the least amount of damage when replacing the pipework.

 

[Agile]

Each sections effective length is multiplied by the number of sections , if the OP had a gas fire added then this would be 3 sections.

You have lost me with that too.

Can you explain in simple language and say why too?