Gas supply question

[Dave Plowman (News]

Including into the boiler? My system 32kw has a 15mm feed into it. But the other side of the cutoff valve only 15mm for a foot or so.

[Andrew]

Presumably the same location for the combi replacement ?.

What size of gas pipe leaves the customer side of the meter at the moment ?.

Since the gas rate of the existing boiler is known then using a manometer to check the pressure drop at the boiler should make it possible to extrapolate the drop at the higher gas rate of a combi.

[Ponyface]

why not install a new boiler and keep the hot water tank and install a pumped shower.

[GB]

They/you need to think more about the hot water outcome they want.

They currently have, say, a 10kW electric shower. The smallest combi is

24kW. This is less than 100% efficient, and there will be losses in the pipework. So, a 24kW combi will provide roughly twice as much hot water as they currently get.

Is twice as much hot water a good enough shower? If not, they will either need a bigger combi or stored hot water. Those are the only (three) choices.

Bear in mind that a horizontal unvented cylinder might fit in the eaves space.

[Dave Plowman (News]

Ideally, yes.

That's something I dunno. Will check next time I'm there.

[Tim+]

It’s really a choice between good hot water flow with no tank (and a new gas supply) or a pressurised tank and keep the present gas supply. Up to them to decide what their priorities are. With a mains pressure cylinder they will still be able to ditch the loft storage tank (unless the HW cylinder is the one I the loft you’re referring to).

Tim

[Andrew]

If it is anything like my house then there will be a 3/4 inch or 22mm feed all the way to the kitchen which will then split into two 1/2 inch or 15mm feeds for boiler and cooker.

[Chris B]

Friend had similar problem, but installer said they would try it with original gas pipework first and if the pressure drop was excessive then an external pipe run would be needed and this would be an extra £XXX on the quote. Turns out it wasn't needed.

[RJH]

In my limited experience it would take an enormous electric shower to get anywhere near the output of a combi

[RJH]

Yes - same here for my 30kW boiler. But mainly 22mm from the meter.

[The Natural Philosopher]

And it would take an enormous combi to get anywhere near the peak output of a stored mains pressure hot water system.

Very few combis can cope with a shower and someone else using hot water. A stored mains pressure system on 22mm pipework can

[Theo]

You can get horizontal cylinders - perhaps it could be mounted in the eaves with minimal loss of usable floor space:

Obviously depends if structurally the wall can take a few hundred kilos of weight.

Theo

[The Natural Philosopher]

Friend of mine has the tank outside in a little boiler house. You can fit a smallish tank almost anywhere.

[Rod Speed]

Plenty of ours are external, nothing added to them, obviously with a cylinder designed to be used like that. Usually on the side of the house which is close to the fence to the house next door, but not always. Works fine.

You can have a full sized tank outside too.

[John Rumm]

Perhaps - the answer is the same though, do the sums and then you know.

[John Rumm]

One thing to keep in mind, is if the manufacturer has stated in the installers manual that it shall have a 22mm feed, then that trumps any calculations, and that is what it must have.

There is - but only once the boiler is installed. You would run it at full output (most boilers have a test mode for that), and measure the pressure at the boilers test point with your manometer / digital tester.

[John Rumm]

That is good point actually - wish I had thought of it! :-)

[John Rumm]

They will have to choose a boiler carefully then - one with a very wide modulation range or otherwise they will likely oversize it for the heating load while trying to get decent hot water performance. That translates to less efficient operation when heating and more wear and tare on the boiler.

[alan_m]

As this is a DIY group there are plenty of on-line web pages detailing how to calculate the pipe size for gas flow, with worked examples.

The calculations are fairly simple based on the length (including equivalent length of fittings , tee, 90 degree bends etc.) and the bore of the pipe and a drop of 1mbar at the the appliance end.

[alan_m]

Presumably the existing shower is electric. Why not just change the shower where the source of the hot water is from the pre heated tank.