New wiki article for review

Perhaps make it clear that the pipe size of a given leg might change en-route and still be complient. Indeed, the union on an appliance may be smaller than the pipe size you need to feed it.

Reply to
Graham.
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One I had bean meaning to write for some time, but it got touched on in another thread, so I thought I might as well do it now:

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Feel free to comment / fix / impove as required.

Reply to
John Rumm

Yup, good points both.

I have added some extra comments here:

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Reply to
John Rumm

I was told that if the union on a combi boiler was 15mm then you could use 15mm, which was handy as it could come off the gas cooker :-)

I don't think we use that Gas Safe registered person much anymore.

Owain

Reply to
spuorgelgoog

:-)

I find you quite often meet the opposite response, where they insist a pipe will need an upgrade, without even doing the calcs. (Presumably applying the heuristic that "combis are high gas rate, and all modern boilers are combis aren't they?", ergo it needs a bigger pipe!)

I once heard an installer say "Ah, you are fitting a modern boiler, they need lots of gas - you will need to upgrade the gas supply to 22mm"

This was a swap from an old 18kW ideal mexico, to a modern condensing Vaillant 418 vented heat only boiler. The fact that they were both 18kW boilers seemed lost on him. The feed was indeed only 15mm, but then it was straight from the meter with an effective length of about 3m. (so good for nearly 3 m^3/h on a boiler that had a peak rate of 1.7)

(However since he was agreeing to supervise and sign off an emergency boiler swap by a non gas safe registered fitter, in rented accommodation, it seemed prudent to not bother trying to win the argument!)

Reply to
John Rumm

One small point: might it be worth making explicit that you can have 2 pipes coming from the meter (well, from a tee there)? Seems to be increasingly common around here (where gas meters are at front and boilers and kitchens at back of Victorian terraces).

Reply to
Robin

British Gas tried that approach when replacing parents' boiler, not knowing Dad previously worked for EMGAS and knew how to do the calcs.

Reply to
Andy Burns

Yup good idea.

I have added a third iteration of the design showing this - dedicated

22mm pipe for the boiler split from a tee just after the meter. This actually produces a cheaper install since it removes 10m of 28mm copper pipe for the expense of an extra 5m of 22mm.

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Reply to
John Rumm

Nice.

I may be being pedantic but I did just wonder if in the third iteration the effective length to the boiler would be better increased to 8.5m to take account of the tee after the meter. Then again, I did also think that might well require me to don full PPE (including box) :)

Also reminds me that the woman who fitted our SMETS2 gas meter told her firm doesn't do anything bigger than 22mm for domestic jobs these days. Her story was that it was just too much faff compared to bashing through a new 22mm.

Reply to
Robin

Small point Perhaps also include the KW consumption of the appliances as well as cubic meters per hour figure.

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Reply to
alan_m

Its already there in effect. In the "Calculate the gas rate" section there is a link to this page:

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That has most of the conversions you could want...

Reply to
John Rumm

Not if you put the tee in such that the straight through direction is toward the boiler, and the 90 tee goes to the lower gas rate other bits.

(which by rights means one ought to add 0.5m to pipe A)

Yup, often the way...

Reply to
John Rumm

3m of 15mm should have been fine for 18kW. But usually the existing feed isn't - the probem is not the kilowatts available, but that modern boilers and current regs dislike pressure drop. Old ones (of both) didn't care so much.

NT

Reply to
tabbypurr

A side issue, but I recently had an argument with the new worktop fitters who were fitting my hob back into place. It had a flexible connection and luckily I caught them just about to change it to solid pipework. They said "flexible isn't allowed any more".

After some "words", then a furious Google, I was able to show that regs say "flexible is ok if the manufacturer says so" or something along that line, and luckily I had the original hob fitting instructions which did say flexible is ok. The guys grumpily conceded they would leave my hob connections flexible, as is.

The gas-fitting FAQ says "Connecting cookers and hobs A flexible hose connection should be used for a cooker."

I guess that needs updating?

Phil

Reply to
Phil Addison

Not to mention the efficiency improvement meaning the new one needs less gas.

Phil

Reply to
Phil Addison

That seems ok to me... you could add the words "free standing" in there to make it more explicit.

Reply to
John Rumm

Just curious (& possibly ignorant) --- the margin between 21 mBar at the meter & 20 mBar needed by the appliance looks rather tight. I assume the appliances also need the pressure not to be above 21 mBar too. Is it not practical to design appliances to accept a wider pressure range?

Reply to
Adam Funk

Its the standard that has been used for a *long* time... Its not that difficult to meet, and doing so saves the operation of one device interfering with another.

Generally, yup.

In reality many do - certainly the more sophisticated devices like boilers etc. Many have their own regulators built in. In practice a boiler may well work correctly down to significantly lower than the nominal pressure (although higher gas rate ones might run into flow rate limitations if its too much lower, even if it can cope with the lower pressure itself).

However you can't assume that all devices have regulators - a hob for example may have the flame lift off the burner if the pressure is too high, or might flame out altogether on too little pressure.

The main danger is when there are concurrent demands that interfere with each other due to lack of system pressure. Imagine the implications of an older hob without flame failure detection, when a boiler fires. That robs the hob of gas and all the lit rings all flame out, the boiler then cycles off and full pressure is then restored to the hob, which is now filling the room with gas.

Reply to
John Rumm

Interesting, thanks.

Reply to
Adam Funk

A standard that has often been ignored in the past. You'd need a sizeable pressure drop to have the hob go out. I've not seen installs that bad. Well, ok I've seen worse, but rarely.

NT

Reply to
tabbypurr

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