Unvented cylinder. G3 reg.s regarding pipe size (D2)

[Mr.B]

I've looked in the current threads and not found the answer to my question, but apologies if it HAS been answered and I haven't seen it.

For the avoidance of doubt I won't be carrying out any work myself.

Here goes .... I've read through the G3 regulations (with regard to the D2 pipe) and also numerous items of advice regarding pipe size, pipe material, the fall on the pipe, sleeving it through walls, the 300mm drop required below the tundish etc.

But I haven't seen any reference to this set of circumstances :-

If I base my run on 8 metres from the tundish to the point of discharge outside, and the installer uses 6 x elbows or bends and uses 22mm copper pipe I get the calculation as follows.:-

9 metres max, less 6 x elbows or bends @ 0.8m each = 6 x 0.8m equals 4.8 m

9 metres less 4.8 metres equals 4.2 metres.

And as my run is 8 metres the installer can't use 22mm pipe.

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That means he would need to move up to 28mm pipe, in which case there's plenty spare capacity as 28mm pipe allows for an 18 metre run and if I subtract the 6 bends (at 1x metre per bend) I have capacity for 12 metres ... and I only need 8.

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My question is .... can the installer come away from the tundish in 28mm and run the bulk of the route in 28mm - but reduce down to 22mm for the last, say, 3 metres?
The only reason I ask is I'm planning the logistics of the route through my bathroom and garage and the last couple of metres would be easier to run in 22mm. To be honest I'm not clever enough to work out exactly what the total resistance figure would be by mixing two different sizes of pipe but I'm hazarding a guess by reducing down from 28mm to 22mm for the last couple of metres and assuming it would comply with regs.
On the other hand it might be that it's not permitted to mix sizes - but I can't see it written down anywhere..

Ta.

 

[muggles]

No, you can't reduce. It must be the same size throughout its length

 

[Mr.B]

That was easy ... much obliged. Nothing more to say on that - the 22mm isn't suitable for that length so it'll be 28mm. Ta.

 

[ianmcd]

28mm copper is stupidly expensive these days there are some much cheaper PE pipe that is suitable for D2, at the end of the day the chances of the pipe having to take a complete discharge are minimal but yes of course do it right

 

[Mr.B]

Yes, I guess it'll cost around £100 for three lengths and half a dozen end feed elbows.

Having said that it's a bit of a drop in the ocean compared to the total cost of the job, should I choose to do it.....

........ unvented cylinder, a replacement boiler to replace the 1995 Ideal Classic FF250 - plus re-siting the new boiler to a different wall in the garage - plus installing a flue out of the tiled garage roof instead of the present wall sited flue. Plus new controls.

I've looked long and hard to see if I could avoid having to run 8 metres of 28mm copper (with 6 bends in the run) but can't see how. There's a soil pipe nearby (adjacent to the bath taps) but it's really tight under there and whilst I could tee into the existing bath waste I realise that's not permitted and I simply don't think we could boss straight into the soil.

I suppose it's physically possible to do the whole D2 run in polypropylene 32mm pipe and take that outside and point at the ground as you would with the copper but I don't know how acceptable (or legitimate) that would be.

My other conundrum is whether to risk pressurising the heating system by using a system boiler ... or fit another heat only and keep the F & E. I realise there are arguments on both sides.

 

[ianmcd]

I suppose it's physically possible to do the whole D2 run in polypropylene 32mm pipe and take that outside and point at the ground as you would with the copper but I don't know how acceptable (or legitimate) that would be.

No reason why you cant, just make sure the PE is temp rated for what you want to do, you will regret getting rid of your Ideal classic, dont expect your new boiler to give you such good service

 

[Mr.B]

No reason why you cant, just make sure the PE is temp rated for what you want to do, you will regret getting rid of your Ideal classic, dont expect your new boiler to give you such good service


It hasn't gone yet ....

Remember, I did say above .... it's a bit of a drop in the ocean compared to the total cost of the job, should I choose to do it.....

And I haven't committed myself yet. In fact I only just had a new fan fitted (I did post a short thread about it a week or so ago)
It's a little bit like Trigger's Broom insofar as it's had a gas valve, an air pressure switch and two fans ... but it was fitted in 1995 / 6 and I've had custodianship of it since 2005 and the bloke I use to fit parts and service it works for mate's rates.

I really ought to simply wait (and wait) until either the boiler becomes un-repairable or maybe until the vented copper cylinder leaks. I've fitted a couple of three way valves and one Grundfoss pump and that's about it. It's had gallons of inhibitor in it.

To be honest if/when the time comes to bite the bullet I'll be frightened senseless at the thought of all that work and the possibility of problems occurring afterwards. I have posted on here before about my uncertainty regarding a choice of boiler. I used to be uncertain, now I'm not so sure.
I WAS just going to swap the heat only boiler and might have gone for Ideal or Baxi due to availablity of installers and spares - and Intergas appeal to me except the installer and spares situation concerns me where I live. Ditto Viessman and Vokera. Worcester is a NO for me and Vaillant is on the fence.

If I went for a System boiler (i.e. with a new unvented cylinder) I think I'd almost certainly settle on an Ideal Vogue.

I'd obviously ask a prospective installer about which unvented cylinder but I don't fancy a bubble top. I imagine it would be an OSO, or Gledhill, RM/Joule, or suchlike.

By far the simplest course of action is to do nothing. But the day will eventually come when my hand is forced (and the day gets closer each and every day).