Gas Pipe Installation and Sizing

[goodgem]

As part of a major extension we have had the gas meter moved outside and the boiler moved to a new utility on the opposite side of the house. This has meant a fairly long run of gas pipe to the boiler and our (CORGI registered) plumber has installed 22mm plastic coated pipe at floor level on top of which will be a UFH system all buried in around a 65mm floor screed.

I have 3 questions really:

1) Is it okay to bury the gas pipe in concrete in this way?

2) Is it okay that the UFH system will heat the gas pipe along with the concrete slab?

3) I've calculated (as best I can) the pressure drop across the 18.6m (inc. elbows, etc.) length of gas pipe from the meter to the boiler (the only appliance connected at present). Based on on estimated 120,000btu boiler size this comes out at 1.24mbar, already over the 1.0mbar 'recommended' limit. I also want to add a duel fuel range cooker and reconnect a gas fire and by my calc's this would bring the pressure drop up to a rather concerning 2.98mbar with everything running at once. Considering the plumber knew of the other appliances, has he installed the wrong size pipe?

Any advice would be greatly appreciated.

 

[ChrisR]

You can put gas pipe, protected, in a screed - there's a section in the books about how to do it, which he should have checked.

Is the pipe too small?
Yes.
Haven't checked your sums but they sound ok.
I wouldn't even bother testing the pressure drop. You always get a bigger drop than the books say. I did a long thing about this...
Anyway, bin the pipe and sack the bloke.
If you put a fussy boiler on the end of that ...

 

[ChrisR]

Found it : 3 up from the bottom of the first page of this thread>
//www.diynot.com/forums/viewtopic.php?t=12871

I remember putting in a tee "for a cooker" which turned out to be a range 18kW on full (about 60,000btu/hr)

 

[goodgem]

That's great ChrisR, thanks for your quick response and it's obvious you know you're stuff.

I've tried working this out in all sorts of ways, using 28mm for the range cooker and gas fire connections from the 22mm pipe, teeing off the 22mm close (within 1m) to the meter and running another 28mm for the range and fire, none provide a satisfactory answer.

The only element of the calc's that may be slightly dubious are the btu/hour rating of the appliances. I have used higher ratings, 37500btu for the range (hob only, 1×1kW, 2×1.7kW, 1×3kW, 1×3.5kW burners), 24000btu (7kw?) for the gas fire and 120000btu (35kw?) for the boiler which I think is actually only a 95000btu but needs replacing because of additional rad's, UFH, new en-suite, etc. Do these numbers sound sensible to you?

Also could you let me know what "book" to look at re. setting the pipe into the screed, I'd prefer to get it right the first time for obvious reasons!!

 

[ollski]

22mm is fine for the 2.9m3 / h that your boiler currently requires but if you are going up to 3.3m3 / h for your new boiler that alone requires 28mm without any additional appliances if the pipe length is 18m....so yes too small.
The regulation regarding pipes laid in screed is in the corgi handbook, citb, viper, tolleys or even possibly in the library in the 'man with fire' book (Gas safety regs).

 

[ChrisR]

YOur figures look close enough - no need to be ultra accurate but remember its the gross gas input and nothe output that matters.
You may find the only way to do it is to take separate pipes back to the meter. Recently put 2 combis side by side, they each had their own 28mm pipe back to the meter. Standard now is a 3/4" meter output - all you can do is go as big as poss asap.

Anything over 28mm is "industrial" - the gas behaves differently in the pipe so you need to do things differently.

Book for solid floors - there's a series if books corgi produce - again and again so we keep havig to buy the new one, which yer man should have.

Here's what some CITB notes I have say - may not be bang up to date but you get the idea: (no I didn't type it all in!)

PIPES LAID IN SOLID FLOORS

Wherever possible, the pipes should be laid on the base concrete. When laid in concrete floors, the pipe must be protected against failure caused by movement. Joints should be kept to a minimum, and compression fittings must not be used.
Three suitable methods of protection are:

1)continuous fully-annealed, factory-sheathed, soft copper tube passed through a larger plastic tube previously set into the floor slab and/or base hard core. Joints should not be located within the larger plastic tube sleeving

2)steel or copper pipe laid on top of the base concrete and covered by a screed. Pipe must be protected by suitable covering, i.e. double thickness PVC tape

3)steel or copper pipe laid into a preformed duct with a suitable protective covering. A soft covering material should be thick enough to accommodate movement and resilient enough to support the concrete cover during setting
Except for corrugated stainless steel pipe conforming to BS 7838, stainless steel pipework must not be buried in solid floors. Galvanised or painted pipes should not be buried without additional protection.


Pipes to be buried in magnesium-oxy-chloride or magnesite flooring, should be of copper with a factory-bonded sheath and jointed with copper capillary fittings. Bends and joints must be protected by wrapping with a suitable plastic tape.
External buried pipes should be of polyethylene, factory-sheathed copper, or factory wrapped steel. All metallic joints must be fully wrapped.

Pipes passing through solid floors should take the shortest practicable route and must be sleeved.
Note: The correct procedures for laying external buried pipes is given in the Institution of Gas Engineers IGE TD/4: Edition 2. Pipes in open soil or below vehicular traffic areas must have a cover of at least 375 mm. Pipes in or below concrete with only pedestrian traffic should have a cover of at least 40 mm.

 

[goodgem]

Fantastic guys, sincere thanks for your advice.

Have discussed with my builder and he is arranging with the plumber to get the pipe replaced for free. Would have been so easy to have been fobbed off but for your advice, so a real result - thanks again.

All the best.