Gas pipe to boiler

[Gasguru]

...........according to the tables, can accommodate 3 m³/h with a 1 mbar drop, adequate for a combi boiler.

Do you actually run gas pipework? since it seems everyone except you know the tables are pure fiction. Often perhaps 30 or even 40% optimistic.

At 3 m³/h you'll be lucky to run 10 meters equivalent pipe lenght without incurrring a drop of more than a mbar. In addition it appears likely the cooker is also fed off this run.

 

[dp123]

dp123 you're missing the (installer's) point.
If a drop of more than 1mbar exists then it's an illegal installation.
The fact that some boilers are more tolerant than others is of no help to you.
Corgi are informed of all new installations, and may inspect.
If they find one where the gas pipe is undersized (drop more than 1 mbar), the installer's in trouble and may be instructred to replace the pipe at his own cost.

Thanks Chris.

What i find really annoying about all this is the guy that came to do the quote was from a big local firm,he never mentioned testing the pipe output ,didn't even look at the meter and just told the wife we needed a new pipe,how could he make that decision without even looking at the outlet pipe from the meter?

 

[chrishutt]

..bear in mind you may have to replace the lot, with 28mm or above.

Well, I don't buy that. If the equivalent length of the whole run is say 20 metres then 28mm would carry 6³/h, enough for TWO 28kW output combis! Even allowing for the tables being over optimistic that is surely overkill. If 15 metres of the run is 22mm and the exposed parts (maybe including near gas meter) were upgraded to 28mm we'd be home and dry.

 

[Gasguru]

What i find really annoying about all this is the guy that came to do the quote was from a big local firm,he never mentioned testing the pipe output ,didn't even look at the meter and just told the wife we needed a new pipe,how could he make that decision without even looking at the outlet pipe from the meter?

He probably knows as we all do that more often than not the pipe run needs to be replaced.

If its marginal its a case of installing the new boiler, checking the working pressure at the boiler and if low then upgrading the pipework.

Measuring the pressure with the old appliance is not always that simple.

Where does the cooker pipe connect? Is it off the existing 22mm run? How far along?

 

[dp123]

Not missing your point at all , CH. As I said, "MIGHT", and you won't know until you measure it.

The OP is getting hung up on and whether it "works" or not, which as you know, is NOT the point.

I am not getting hung up on condensing vs non condensing boilers, i am getting hung up on the fact the guy that did the quote has told us a 22mm pipe running round the rooms (adding more length) from meter to boiler will be up to the job for the condensing combi when the existing 22mm pipe is not, bearing in mind he doesn't know its 22mm as he didn't bother to check.
If the existing 22mm is the full run minus the last 2 meters then surely it has got to be better than a 22mm pipe run around the rooms with all the elbows needed?

 

[chrishutt]

Do you actually run gas pipework? since it seems everyone except you know the tables are pure fiction. Often perhaps 30 or even 40% optimistic.

Yes I do run gas pipework, but I actually ream the tube ends so maybe my experience is different to yours . Seriously though, I haven't properly assessed the accuracy of the tables, nor do I know of anyone else who has. I'm willing to accept that they are optimistic, but I find it hard to believe that the tables are "pure fiction" though, or that they are as much as 40% out.

 

[dp123]

He probably knows as we all do that more often than not the pipe run needs to be replaced.

If he had looked at the pipe at the meter end than told us it needed replacing i would have taken his advice and got on with it.
I am really glad i found this forum as there is now a chance be it a slim one that the pipe may not need replacing.

Where does the cooker pipe connect? Is it off the existing 22mm run? How far along?

I have looked behind the cooker and the pipe that exits the wall looks to be 22mm and then goes into a 90 bend where the hose is fitted to it.
The cooker is approx 6 meters from the meter.

 

[Agile]

Thats probably a 1/2" iron pipe which is the equivalent of 15 mm copper as its about 22 mm on the outside.

Tony

 

[chrishutt]

Measuring the pressure with the old appliance is not always that simple.

In principle it's perfectly simple, but the measurements will need to be accurate (preferably with digital pressure gauge), especially if the boiler is only running at a lower gas rate for heating.

 

[Gasguru]

So the cooker probably tees off the main gas run to the water heater. Your chances of retaining this existing feed to the boiler are looking even more remote. The cooker would typically add another 50% gas flow rate on the pipe.

In the case of the tables, every discussion on this forum and the other rgi forums have all found the tables to be widly optimistic even with well prepared pipework.

I had a job last week, all newly installed by a local installer (high quality top notch work), 2.6 m/hr to a combi, 9.5 meter actual lenght of 22mm, 5 elbows giving 12m equivalent lenght. The measured drop was a shade over a mbar. The tables would tell you it should cope with 3.9 m/hr that's 50% over the actual flow rate. I know some gas valve isolating valves can be a little restictive but this boiler had a 22mm connection and isolating valve so negligable loss.

 

[Gasguru]

In principle it's perfectly simple, but the measurements will need to be accurate (preferably with digital pressure gauge), especially if the boiler is only running at a lower gas rate for heating.

In reality the water heater may not produce its full output due to low mains water pressure, partially siezed mechanical components etc. I very rarely see water heaters produce anything like their quoted inlet KW. So we won't have a sufficient load on the pipe.

Also the final connection is on very undersized pipework so its a fairly futile excercise. We can also assume the cooker tees off the run.

 

[bengasman]

30 metres of gaspipe to a combi in 22? Unlikely, as you will need to add several metres for the bends. More likely to be 28 unless it is a very low capacity combi. Any rgi should realise that before getting the tables out to verify. If your installer did not spot that, it might be wise to find another one. £600 for a new 30 metre long gassupply does not sound overly expensive if installed properly.

 

[ChrisR]

He's got a 24kW water heater now so it should be simple enough to measure. Idon't remember about the OP's cooker and/or fire position, but remember you're expected to leave room for some additional load.

I've measured long runs of gas pipe with all joints very carefully, completely deburred, with long radius elbows, and always found the tables to be a long way out. One I remember, 28mm at the limit on length, gave nearly double the predicted drop.
Existing pipework is usually put in with far less care, dirty etc, and can give 3 times the drop in the tables. One blob of green growth from using the wrong type of flux and you're stuffed.
Recently I measured a 2mbar drop in a short length of iron which should have been about 0.5 mbar, so I blew it out with a vac (DIY'ers DON'T do this, you're liable to blow yourself up!) and got it down to 1mbar.

I'll bet a pound that he OP's installation would be undersized if it's all 22mm!

 

[chrishutt]

One I remember, 28mm at the limit on length, gave nearly double the predicted drop.

If you're consistently finding the tables out by 100% have you considered drawing the attention of "the authorities" to this? It's pretty outrageous if the whole gas industry is operating on the basis of tables that are 100% out! If that really is the case, and I haven't got any evidence against it, then I take back what I've been saying.

 

[Balenza]

dp123 wrote in his opening post.

We have a water heater and a gas boiler in the garage at the rear of the house.
The meter is in the front of the house and approx 30 meters from the garage

Then dp123 wrote

I have also accurately measured the distance from meter to garage and it is not 15 meters as originally guessed but 11.

Your original guess I have to assume is the 30 meters mentioned in your first post.
Perhaps this guess was in feet ?.
Where has the 15meters came from ?.
Why has the distance suddenly halved ?