Disruption to my period home with Installation of new boiler

[michael]

A reputable plumbing company in my area has advised me that to replace my existing ten year old combi boiler with a new condenser boiler will require upgrading the gas supply pipework from 22” to 28”.is this true? In my case it would require a run exceeding 50 ft and would cause considerable disruption with the removal of boxed in panels and floor board lifting let alone the cost of running 50 ft of 28” copper.

 

[Flyfisher]

Well, a 22-inch gas pipe seems pretty enormous, so an extra 6 inches shouldn't make much difference. :wink:

Seriously, I guess you're referring to mm rather than inches (")!

We had gas connected to our house last year and had the meter located in a outbuilding to avoid those horrible boxes on the house itself. This meant a long connection from the low-pressure side of the meter to the new gas boiler. I recall the gas fitter being concerned with the distance (around 40m) to the boiler and I think he may have used 28mm pipe - I can check tomorrow if it would help. Fortunately, our gas pipe was mainly external to the house and the boiler was hung on an outside wall so there was minimal pipework inside the house.

I don't know the specifics of your case but the issue is all to do with pressure drops along the gas supply pipe between the meter and your boiler. The pressure at the meter will be X and the boiler will require a minimum pressure of Y. There are standard calculations to determine the pressure drop along each metre of specific diameter pipe. Each bend or tee will also introduce a pressure drop. Our fitter was careful to maximise the bend radius of the pipework in order to minimise the pressure drop.

You could, perhaps, ask your fitter to explain his reasoning for needing 28mm pipework and ask to see a worked example. Perhaps a different model of boiler might be tolerant of a lower pressure supply? Perhaps it would be possible to use a different route for the new pipe, maybe even running it outside, and just disconnect the old one in situ? It might even be an option to relocate the meter closer to the boiler, thus reducing the supply distance and consequent pressure drop (the gas company side of the meter is high-pressure so distance and pipe size is less of an issue, in a domestic context anyway).

I don't know if these points can help your particular circumstances but they are the sorts of questions I'd be asking before resigning myself to tearing apart the interior decor.

 

[Penners]

An excellent, comprehensive answer from Flyfisher, there. My only additional comment is in the form of another question.

Not being a gas user (ever), I'm amazed that the pressure in a gas supply pipe can vary from place to place. My crude knowledge (and "knowledge" is really far too strong a word!) of physics suggests that, when a vessel holds a pressurised gas, the internal pressure is the same in every part of the vessel.

Is that not the case? :?

 

[michael]

Thanks Flyfisher
Sorry yes mm not inches. I’m always thinking in ‘old money’ when dealing with these old properties.
Basically, the gas comes in from the street at one end of the building onto the internal meter in a small cupboard and the boiler is located at the other end of the building in a convenient out of the way place. I guess it would be easier to try and relocate the boiler closer to the meter but this would probably upset the pipe sizing on the radiator system(largest pipes nearest the boiler smallest pipes at the end of the run) so swings and roundabouts on that one I think.
Outside runs are not really an option on my property as the gas comes into the building from under a public pavement and my building abuts the pavement.
The fitter advised me that all domestic condenser boilers require a 28mm gas connection, something to do with them requiring more gas on start up compared with the old combi boilers. I would like to know if this is true.

 

[Flyfisher]

Not being a gas user (ever), I'm amazed that the pressure in a gas supply pipe can vary from place to place. My crude knowledge (and "knowledge" is really far too strong a word!) of physics suggests that, when a vessel holds a pressurised gas, the internal pressure is the same in every part of the vessel.

Is that not the case? :?

Last year I would have been equally perplexed. In fact, you've cunningly disguised an apparently simple question within two operating conditions, so the answer is yes and no. Yes, in a closed vessel (including a series of pipes) the internal pressure will be the same in every part of the vessel but, no, in an open vessel - which is effectively the case of a pipe between a meter and an operating boiler - the pressure can and will vary according to the rate of gas flow, the pipe diameter and the amount of turbulence introduced by tees, angles and even straight joints in some cases, plus a whole bunch of other factors as well. The key requirement is the need for the pipework design to be capable of delivering the operating pressure required by the boiler. Google "gas pipe pressure calcs" to find (loads) more info, including some pretty comprehensive software to handle some serious engineering calculations.

My level of 'expertise' in this area has thus increased dramatically from being blissfully unaware of the whole subject to now knowing for sure that it's actually quite complex and I don't really understand it at all. It's given me a whole new respect for those Corgi chappies, or whatever they're called these days.

 

[Penners]

I've done a bit of rootling around the electric interweb, and it seems that condensing boilers generally require a 22mm gas supply pipe for smaller models and 28mm for larger models. So, assuming yours is the latter, 28mm seems to be kosher.

What's the make and model of the proposed new boiler?

 

[Penners]

My level of 'expertise' in this area has thus increased dramatically from being blissfully unaware of the whole subject to now knowing for sure that it's actually quite complex and I don't really understand it at all.

Well, given my question above, I'm actually quite proud to be in your "don't really understand it all" camp. Mind you, I think we are at different ends of the "don't understand" spectrum.

Many thanks for your explanation.

 

[Jon Maine]

We had to have a section of 28mm pipe installed, not all of the way but a fair way just to help keep the pressure correct. Not sure how it works but it solved our problems.

 

[Flyfisher]

The fitter advised me that all domestic condenser boilers require a 28mm gas connection, something to do with them requiring more gas on start up compared with the old combi boilers. I would like to know if this is true.

My inclination is to disbelieve it as an absolute requirement in all cases because I got the firm impression from our gas fitter that it was the distance and pipe layout that was the important factor. Penners' post also seems to support that.

Our fitter also made a point of asking if we were planning on having a gas cooker as well (we're not) because that would have required an even larger pipe to have been used to allow for a tee and the pressure drop when both appliances were operating. I also doubt that a 28mm pipe would be required if the meter was next to the boiler. A domestic boiler might have a 28mm gas connector, but that's not the same as needing a 28mm supply pipe in every case.

Jon's experience also makes sense and might be applicable. By using a large pipe for the first part of the run the pressure will remain higher for longer so the final pressure might not drop below the boiler requirement over the last (and now shorter) bit of thinner pipe. If that makes any sense.

I must again stress that this is all amateur rambling based on very limited knowledge, but it might help to formulate some pertinent questions.

 

[Feltwell]

Totally ill-informed comment here, but here goes.....

Your old boiler was a combi, your intended new one is condensing but is it also a combi?

We replaced a standard non-combi boiler with a condensing non-combi boiler, so we still have a hot water tank. The boiler has to heat a 3 storey 5 bed house. It runs quite happily off a 15mm gas feed pipe, although it is quite a short run from the gas meter (probably no more than 3m).

We have 22mm running off the meter, which then splits to 4 x 15mm feeds (boiler, cooker, gas fire, gas poker connection)

Maybe you could investigate if having a "standard" condensing boiler with hot water cylinder instead of a combi will reduce the need for the gas supply to be so large? As a combi has to have an "instant" effect when you turn the hot tap on, maybe it needs more gas at those moments than a "standard" boiler that is gradually heating the hot water cylinder contents.

But - I could be talking out of my rear!

I've found the plumbers forum on Screwfix's website to be useful on occasions for getting opinions of those in the trade.

 

[JoceAndChris]

Thanks for the recommendation of the plumber's forum Feltwell, very useful indeed and will be stored as reference for future major work to be carried out by poor father-in-law.

 

[chuckey]

My gas boiler is 85000 BTU O/P because its about 30 years old, I doubt if its efficiency is above 60% so for an equivalent gas consumption a modern condensing boiler would be rated at 90/60 X 85,000 or 127,000 BTUs. The boiler pipework as installed (from the meter) was 6m of 3/4" copper, then 7m of lead (3/4"?), then 3.5 m of 3/4" iron when it split into two feeds, one for the cooker the other via 1m of 1/2" copper to the boiler. Seems to work OK, your quoted pipe sizes do seem to be VERY big for an efficient boiler ( or is it a big boiler?).
Frank

 

[Jon Maine]

Things have changed, the requirements are different for reasons I either don't know or can't recall.

 

[Aidan]

Spot on, Mr. Flyfisher.

An excellent, comprehensive answer from Flyfisher, there. My only additional comment is in the form of another question.

Not being a gas user (ever), I'm amazed that the pressure in a gas supply pipe can vary from place to place. My crude knowledge (and "knowledge" is really far too strong a word!) of physics suggests that, when a vessel holds a pressurised gas, the internal pressure is the same in every part of the vessel.

Is that not the case? :?

It is, when the fluid is stationary. When fluid flows through a pipe or duct there is a loss of energy due to friction and the energy loss causes a loss of pressure. Also the fluid flows from the high pressure region to the low pressure region.

At times of peak demand there are significant pressure losses in the mains. However the mains operate at a higher pressure than the installation in the house and there is a governor (pressure reducing valve) on the meter. The only concern is the pressure losses from the meter to all the appliances. The pressure loss from the meter outlet to each appliance must not exceed 1 mbar at the maximum load.

I wouldn't be inclined to trust the gas fitter to have made precise calculations, but everyone will tend to oversize the pipe rather than risk getting it wrong and having to pay for it to be re-piped.

 

[Aidan]

The fitter advised me that all domestic condenser boilers require a 28mm gas connection, something to do with them requiring more gas on start up compared with the old combi boilers. I would like to know if this is true.

No. Read the manufacturer's installation instructions for the boiler proposed, usually available on the web. It usually has to be 22mm to within 1 or 2 feet of the boiler. A larger size tube may be required for a long and/or convoluted run causing excesssive pressure losses, as descrbed above.

 

[Flyfisher]

Just to put some numbers to my previous post, I've measured our gas pipework:

Meter ---- 1m x 28mm copper ---- 35m x 32mm Plastic ---- 2m x 28mm copper ---- Boiler

The boiler is a Valliant ecoTEC plus 624.

I don't know the internal diameter of the plastic pipe but I doubt it's more than 28mm. It has quite thick walls and is intended for underground installation, albeit within a separate conduit pipe.

Given that 28mm seems fine for our 120 feet of gas piping, it begins to look as if this could be overkill for 50 feet - as per Aidan's comment about the gas fitter 'playing safe'.

Anyway, food for thought. Please let us know the eventual outcome.

 

[Aidan]

Just to put some numbers to my previous post, I've measured our gas pipework:

Meter ---- 1m x 28mm copper ---- 35m x 32mm Plastic ---- 2m x 28mm copper ---- Boiler

I trust that the 32mm plastic is external; internal plastic pipes are verboten.

Another approach would be to measure the existing pressure loss between meter outlet and the inlet of the existing boiler at the peak flow rate, measured by the gas meter. Knowing the pressure loss at one flow rate, it is a simple calculation to work out the pressure loss in the same pipe at any other flow rate. You'd need an accurate digital pressure meter, not the U-tube water manometer most gas fitters have.

On a more important topic, how would you suggest I'd go about learning to cast a fly? It's one of those things I've always wanted to do, but never got around to.

 

[skier-hughes]

Get a good experienced flyfisher to show you how!!
I await a good written description!!

 

[Flyfisher]

I trust that the 32mm plastic is external; internal plastic pipes are verboten.

Yes. The meter is in an outbuilding and the short copper pipe connects to the plastic one, which was laid in a 21-inch trench inside a yellow conduit. It then reconnects to copper where it exits the ground at the house. The boiler is mounted opn an external wall and the gas pipe goes through the wall and straight into the boiler. I can't actually see the gas pipe inside the house.

On a more important topic, how would you suggest I'd go about learning to cast a fly? It's one of those things I've always wanted to do, but never got around to.

Now that's a dangerous question and could easily provoke the biggest post ever, so I shall try to retrain myself.

If you've never tried at all then it'll probably be worthwhile arranging a lesson from a registered flycasting instructor. It's not rocket science but without understanding the basic principles you'll probably struggle to practice effectively. For example, you don't really cast the fly in the same way as casting a weighted bait or lure (it's far too light), you're really casting the fly line so technique is key. Game or country fairs often have stands offering free 'have a go' flycasting with instruction and this can be a very good introduction.

There's also the type of flyfishing to consider. Trout or Salmon? Dry or wet fly? Single or double-handed rod? While the basics are similar, the different types of flyfishing are more or less tolerant of casting technique. For Salmon fishing, a 'dainty' presentation of the fly is less important than being able to cast a long line and thus cover as much water as possible. For dry-fly trout fishing on a river, good presentation is far more important than distance as you can usually get fairly close but may only have one chance of gently dropping the fly in just the right place without spooking the fish.

Once you have your chosen rod and line and a basic understanding of the principles from a friendly fisherman or instructor then it's really just a case of practicing. I used to practice casting to a hat in a suitable field - use a fairly large fly (e.g. mayfly) and snip off the hook to avoid it catching everywhere (and, incidentally, always wear glasses when flycasting!). 30-40 minute practice sessions will soon improve your technique, but don't over-tire yourself as your casts will worsen and you'll get frustrated.

I think that's enough before we get chased off by the thread-drift police. PM me if you have any other questions.

 

[Penners]

It's not rocket science

No, it's much more difficult.

A decent rocket scientist can learn his trade in 5 - 10 years. A flyfisherman is still trying to get it right on the day he finally floods his waders and sinks to a watery grave.

:wink: