Gas supply question

I think that it was mentioned earlier that they want to build a staircase through where the tank is and don't want to lose the space elsewhere.

Which is all very fine if the pipe isn't buried. If it was easy to see, it would be easy to replace.

I don't really see how you do the sums, though? Most of the present supply is buried out of sight, so theoretical calcs are really hit and miss.

Ideally, an empirical flow test is what is wanted, but what do you do with the waste gas? Flare it off, like an oil rig?

As Andrew mentioned higher up the thread - you can work backward from the current installation. If you do a pressure drop measurement with the current boiler running at full output. Since you know the gas rate[1] of that, it should be fairly easy to arrive at at least at a "no go" conclusion... e.g. if the current boiler is 12kW and the one you plan to install 24kW, and the pressure drop difference between meter and boiler is already 0.9mBar, you know that it is not going to cope with a 100% increase in gas rate.

You may be able to deduce more if you can make a guestimate of the overall pipe run length, and see what diameter it is at least in some locations.

Perhaps they could save space by removing the bath.

My limited experience suggests combis are crap for running a bath.

A bath is a lot more water than a shower, and it will be a pain when they realise it's going to take over 10 minutes of continuous running to fill the bath. By which time it may be cold...

Andy

Is the input to the floor 15mm or 22mm? Is the output from the floor 15mm or 22mm? Is the location of the pipe run known.

If the input pipe size into and from the floor is the same then perhaps this suggests what is under the floor is the same pipe size.

The length of the run can be estimated. Unless the pipe run is rather convoluted then the only T piece will be to the now redundant cooker. The number of 90 degree bends are likely to be fitted before the pipe goes into the floor and after the pipe leaves the floor.

The sums based of equivalent pipe length and pipe bore can give an estimate to see if the original pipe run was more than adequate for the existing installation or if it was marginal, and give some indication if it would be suitable for a larger combi boiler.

Albeit £2k+ a combi boiler with a built in hot water tank

Friends of mine have have an oil combi boiler and although it is a largish floor standing lump it has built in hot water storage. The boiler fires occasionally to heat this tank, as well as firing when their is a call for water. This allows a powerful pumped shower to have hot water for lengthy periods.

Fair enough, so you use the existing boiler to flare off the gas. :)

One small issue is that boiler ratings are not exact. It may say 12 kW, but what it actually consumes could easily be +/- 10%.

uninspectable gas pipes in maybe corrosive conditions are not a good idea. Sure, they work, but are not recommended.

Use of a waste water heat exchanger can change the calculations & options,and save run costs. Make your own if you want it at a sensible price.

Indeed. You need to read the spec carefully to work out if they are talking input power or output. Most will normally give a max gas rate somewhere in the installers manual. However there will always be some variation since the energy content of the gas itself is not fixed among a number of other variables.

The calcs are not that difficult, but do seem to beat some gas installers. I had the same problem, gas fitter didn't investigate, just made an assumption, which would have need a new long pipe right around the house wall. A bit of investigation and a few calcs by me, and it was fine to reuse the existing.

Bad assumption. My 1976 house had 3/4 inch screwed iron piping entering in the lounge through the floor behind the baxi bermuda back boiler then continued along the end gable wall (buried in screed) then a 90 degree right turn into the kitchen and half way along one side of the kitchen it went into a 3/4 T junction with the other two exits sleeved down to 1/2 inch, one continued along the wall, the another 2 or 3 90 degree bends until it exitted behind the cooker into a flush-fit bayonet connector. The other exit from the T piece was also sleeved down 1/2 inch and did 2 more 90 degree bends and then stuck out of the wall just above the skirting and was simply capped off. This was for a gas fridge.

There was no way of knowing that there was a run of 3/4 inch all the way from behind the back boiler into the kitchen. I asked the BG sevice guy once about having a wall mounted boiler in the kitchen and pointed to this