Unnecessary work???

[Black Shuck]

Doing a new kitchen myself, thought to be on the safe side, got a Corgi = =

registered company to sort the gas out.

However, I think they may have done unnecessary work.. Thought I'd ask = =

here to see what others think..

My existing gas point basically needed moving 1 metre, from 1 wall, to t= he =

corner of the same wall. I lifted the chipboard ready for the gas fitte= rs =

arrival. On arrival however, he explained that a 13mm gas feed is =

insufficient for a double gas oven and 5 hob gas stove, and needed a 22m= m =

feed, pointing to the underside of the combi-boiler, as an ideal spur. = I =

kinda went with his recommendation.

A couple of days back, they came back to do the work (I had to remove =

additional bits of the old kitchen to facilitate running the new pipe, =

hence the delay).

To my suprise, they ran 22mm from the boiler halfway along the wall, the= n =

fitted a reducer down to 13mm, then another meter, did a 13mm spur for m= y =

hob, and the rest of the feed in 13mm.

Crude pic here:

does this differ from the original setup of extending the original =

13mm pipe installation? Surely the flow is restricted by the smalled =

pipe? So even the new setup is limited by the last run of 13mm pipe? I= =

would have understood things, if they T'd off the 22 with 2x13mm spurs, = =

but they did not...

Have they created unnecessary work???

[Andy Hall]

This is a case where length matters.

Resistance to flow depends on pipe lengths and fittings as well as diameter.

Take a look at this

design may well be reasonable.

The acid test would be to make pressure measurements at the meter and the two appliances and to check that there is not more than the allowed

1mB drop in pressure.

[Ed Sirett]

Have a read of the Gas Fitting FAQ - there's a section on this.

By 13mm you mean 15mm?

My guess/feeling/intuition is that they were right and probably the pipes needed to be bigger still. Quite probably with hob and double oven the supply in 22mm to the combi is now under sized.

I'm surprise they didn't carry on in 22mm until the first T to the appliance, there may be some small clearances or other awkwardness.

If you care to list out the following information I or someone else can do the numbers. It will depend a lot on where the gas meter is located.

Size and Lengths of pipes all the way from the meter to the appliances. Number of T and L fittings in each pipe.

Rated maximum heat input of each and every appliance.

[Christian McArdle]

This is where you misunderstand. The smaller pipework doesn't limit the flow rate, it just provides resistance. A little bit of 15mm won't harm. It is long runs of 15mm that cause the trouble.

Hence 10m of 22mm pipework followed by 1m of 15mm pipework is almost as good as 11m of 22mm pipework and is much, much better than 11m of 15mm pipework. If you see what I mean.

Think of it as a road network, with 22mm being a nice motorway and 15mm being a twisty B-road, but without any queues. You don't mind a bit of twisty B-road at the end, provided you cover most of the distance on the motorway.

I have no idea if their design is sufficient, though. A large cooker and combi boiler (i.e. at least 24kW, probably more) can be quite limiting on

22mm pipework. My installation has 28mm until the boiler/cooker tee and then continue in 22mm until the appliances, although the runs for both are quite long, particularly after the tee.

Christian.