Estimate gas pipe capacity.... Main Medway

[DIYSOS]

I have an existing 22mm gas pipe run, currently serving an old (multipoint?) on-demand water heater. I'm looking to install a new CH boiler, and would like to estimate the max boiler (KW/BTU) that can go onto the end of this run without incurring the (not insignificant nowadays) Corgi cost of upgradiung this pipe.

a) The 22mm pipe is about 10m long, runs along outside walls but has 8 x

90degr bends along the run. Nothing else braches off it, just the old boiler at the end. I wouldn't know the pressure at the meter. Can this be calculated?

b) Alternatively, the existing on-demand water heater is a 'Main. Medway (automatic)' . It's about 420 x 750 and was in the house when I moved in (1988) and would guess it's early or mid 1980's. It has a distinctive winter/summer knob in the bottom right hand corner. I'm guessing it might be

20KW but don't really know - if you have one of these, and/or know what the power rating is please let me know!.

Thanks,

DIYSOS

PS - hope a) doesn't prove to be smaller than b) !!!

[DIYSOS]

Sorry I mean can the pipe carrying capacity be calculated - not pressure at meter.

[Alan]

In message , DIYSOS wrote

The following link may help

[John Stumbles]

Each 90 deg bend is equiv to 0.5 metre pipe length so you've got 14m equiv in all. I'm not looking up the tables and charts (you don't get everything for free :-) but off the top of my head you start getting into trouble with a 28kW appliance at about 20m of 22mm pipework, so 14m should be OK for similar. If you need 35kW maybe you should be thinking of more insulation, alternatively you have such a big and expensive house you can affort to pay someone to work it out for you :-)

I don't know the rating of the water heater but it sounds as if the pipework was generously specced for it.

[DIYSOS]

Many thanks for the helpful replies.

OT, now this probably can't happen but...

I seem to be staring at 2.5k to 3k to fit a new central heating boiler for a DIY CH system.

So, I'm amused by the concept of re-using the existing GWH to power a thermal store. IE take it off the mains water supply, and re-plumb into a primary water loop with thermostat and pump feeding the store. The 'stat starts the pump and the flow fires up the boiler - in theory!. Space heating and DHW taken off the store as usual. No new boiler and better still no Corgi - cost virtually nothing!.

Like I say, for various reasons this probably can't happen, it might even be dangerous (so don't try this at home, OK?) though I can't think why unless water runs out?. And the boiler would be working for hours on end, not just

20 mins a day... and I know it's probably SEDBUK Z. But I can dream!.

Cheers,

DIYSOS

[DIYSOS]

... of course I'm 3 years too late anyway, being SEDBUK 'Z' boiler would fall foul of Part L anyway.

Anyway I digress... thanks again for the earlier replies.

DIYSOS

[Paul Barker]

I'd allow for a few sockets also and say 15m of pipe which gives you 3.

m cubed per hour. The calorific value of natural gas is 10.76 so you ca use a 35.5 kw appliance on the end of this pipe run

-- Paul Barker

[Doctor Evil]

It is not dangerous at all, it will work. This sort of thing is common in the USA. Chaffotaux made an boiler with multi-point controls about 20-25 years ago. The pump pressure opened a water valve.

Boilers are so cheap these days it is probably not worth it.

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[Andrew Gabriel]

The Main range are all around 30kW input (different models varied by a couple of kW). I've got the spec of the Main Medway hidden somewhere if someone wants the exact figure.

[Andrew Gabriel]

Mine measures at 77.2% efficient, which makes it SEDBUK E (actually, only 0.8% off from SEDBUK D -- would probably get there with some fine tuning).

Unlike a conventional stored water system, there are no losses from a cylinder or primary circuit, so you would need to adjust this upwards to compare overall system efficiency with that of a conventional boiler and stored water system.

[DIYSOS]

Wow 30KW!. And that applies to my 1980's model. Makes wonder why my shower isn't warmer - I've a vague suspicion limescale has built up over the years and never been removed during servicing, but I can't be sure.

DIYSOS

[DIYSOS]

Boilers may be 'cheap' but putting one in certainly isn't (:->) - unless you DIY it, of course.

So this idea actually seems doable and the boiler efficiency is almost acceptable then (before April at least). So near and yet so far - I'm almost glad it's hopelessly situated in a bedroom wardrobe to make me feel better about not trying it out.

DIYSOS.

[Andrew Gabriel]

I used to take the heat exchanger out occasionally, stand it upside down in an old plastic bath, and pour descaller through it until it stopped fizzing. Made an enormous difference to the performance. This was a 1978 Main Medina, which had no thermostatic control. It was too powerful for a shower (choice of being burned, or having the water jets drilling holes through you), and you couldn't turn it down. I replaced the whole thing in 2000; see

replacement unit has thermostatic control, better modulation control, and has internal teflon coated pipework which hasn't scaled up since.

[nick smith]

.....sssnnnniippp>

What's happening in April ?? are we all going condensing or something ??

Nick

[Doctor Evil]

Having an existing multi-point heat a thermal store is no problem, even after April. It is already there. It is not a replacement or a new installation.

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[DIYSOS]

I did wonder about this, the boiler installation is indeed not new (in fact it's very old!) but the change of use is very radical!.

Indeed we are.

DIYSOS

[Doctor Evil]

It's not radical, it is heating water by gas, just as it always has done.

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[DIYSOS]

Very true... but what about this boiler interlocking... how to connect 'roomstat' to the boiler... would it *really* be every bit a safe as a modern boiler if used this way - and readily seen as such should I sell up... ie would the new setup 'pass' CORGI inspection... how long would this boiler last if used flat-out for hours on end instead of 10 mins a day (probably longer than a modern one!), what about running costs and the planet... and as it's a new CH system with no Corgi involved, am I supposed to raise a Building Notice?.

These are some of the unanswered questions in my mind that may or may not be valid, but fortunately I don't have to addrtess them - yet!. The boiler is in a bedroom where my thermal store (or HW tank) would probably need to go, so I'm unlikely to proceed anyway - until I find out how much the new boiler installation will be, of course!.

As my old boiler was really an OT subject, and my original question about the gas supply have been comprehensively answered, I plan to bid this thread farewell - so thanks all for your input.

DIYSOS

[Doctor Evil]

As you have a heat bank between the boiler and the rads the boiler is not connected to the rads. The boiler operates not even knowing the rads are there just heating the water mass. The cylinder stats act as the interlock.

Corgi is interested in the gas safety side. A multi-point connected to a thermal store has an interlock via the cylinder stat. The stat controls the pump. The pump is on the return to the multi-point and opens the gas valve via pressure.

Does the multi-point have a thermostat?

A modern boiler will be far cheaper to run.

Not that I an aware of. Others may know better.

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[DIYSOS]

I think so, though as it seems to be heading for the skip I doubt this will count for much...