Flue Liner or Not

24 Nov 2007
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United Kingdom

New here so please be gentle with me.

Right straight to the point, i'm collecting the bits so that I can fit a new heating system before the old one dies, I've got 2 x 28KW gas condensation boilers to replace the old one, question is about the flue, the boiler will go in the basement and there is the existing chimney which is used as the present flue, but no flue liner fitted.

Q1. Do I have to line the chimney? (no fireplaces fitted)
Q2. Can I use plastic pipe?if so, any type, is soil pipe ok?
Q3. Hot gases rise so no problem with gases coming back through 2nd boiler if not being used?

Any recommendations would be helpful
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You have to be competent to legally carry out your own gas work...and clearly you havn't the faintest idea what you're doing.

2 x 28 Kw. What sort of property is this - commercial?

What boilers are they? Are they new? Where from?

Flue pipework is either provided by the manufacturer or they provide the spec for the flue pipe ie 50mm MuPVC or CPVC etc.

A few manufacturers provide flexible flue pipes specifically for chimneys, however reports are that the liners cost as much as the boilers.

Cascaded (joined) boilers have flue components specifcally designed to link the boilers. However its not just a case of "joining" boilers together, what control systems are to be used, are low loss headers required etc etc.

This installation is very large domestic or commercial and no diy task (especially one asking such basic questions).

There are at least 10 documents I can think of that you need to comply with for a start.
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Never said I was qualified to do this job, shall we say project manager.

This is a large domestic property with only 2 people living here so 2 x 28KW boiler that happened to come my way are about right, both boilers will have 3 zones so effectively the heating will follow the occupants around the house in their daily routine, each zone having it's own timer/thermostat.

These are new boilers, Chappee Luna WGB 2C (Baxi)

80mm flue outlet and yes the price of the flue is very expensive hence my questions, if it had been a normal boiler then I wouldn't have asked but as flue gas tempretures on condesation boilers are only about 55C then surely it's possible to use normal soil pipe as the flue???? after all looking at the boilers thats all the manufacture's use.

Maybe I should have posted more info in the first place, but I'm just collecting the bits for a qualified engineer to install the system next year, I'm not a heating engineer but I can do most of the pipework etc under instruction, so not an idiot, just ain't got much money, and a logical mind.

Right straight to the point, i'm collecting the bits so that I can fit a new heating system before the old one dies,

Try fitting it then fire it up, you`ll have lots more `bits to collect` afterwards, :D most of them, yours.

Any recommendations would be helpful.

I recommend you pay a qualified gas fitter to come around, listen to your proposal, asking him to kindly stop laughing hysterically, then give him the job. ;)
Bamber Gaspipe

Thanks for your comments, I should have posted more clearly my intentions, perhaps you'd now like to comment on the updated post obviously posted 2 secs before yours.

Not here for any arguments just useful advise :oops:
"Project manager" reads first time property developer who paid top whack for a bag 'o nails. :D

And I guess the "house" is located in France, although a house requiring 56Kw is more like a 10 bed Chateau. :)

The boilers appear to be Brotje WGB 2 complete with twin pumps for a cylinder and heating circuits. The manuals are comprehensive but only a call to technical will confirm if they are cascadable.

They look top of the range ie complex to setup properly and therefore may have very few that understand them fully. Competent gas work on the continent is hard to find apart from Germany/Netherlands etc.

Manufacturers make their profit from the flues, hence they are often a rip off price for bits of plastic, trouble is you have bo use their approved system for safety.

You need to find someone competent now to design the system to get the most benefit from these boilers.
Looking at the Chappee Luna on the interweb it would appear it is not a condenser. However, since the manuals are Belgian Baxi speak it is difficult to know how many varieties of Luna there are.

If the OP would clarify the install is not in the UK it would help, because no one with an ounce of common sense would try and fit them in the UK.

The OP is clearly a numpty project manager because as any boiler installer knows, the flue is the bit you worry about first in any prospective installation. It is unbelievably naive to buy some hokey cokey boilers and then worry about how the flue can be run.
"Project manager" reads first time property developer who paid top whack for a bag 'o nails. Wrong!!!!!! and the roperty is not in France bit is in Holland.

The boiler are not the twin pump spec, heating only, no hot water.... these boiler will not be connected in cascade.

System has already been fully designed around the boilers which came FOC, maybe that explains more to you :LOL:

Yes rip off prices indeed, nearly £1000 for 2 x 17m of plain plastic pipe, thats why I'm asking the question, use plain soil pipe, can anyone tell me why not????building regs apart.
Thanks GG

That does indeed look rather tasty, seems to be a 'proper' system boiler with weather comp etc .

As you say it doesn't bear much resemblance to the crud Baxi are peddling in the UK market.

And it appears suitable for an open flue... very similar to the Viessmann 300 series.

Anyone speak Belgian? Apart from Rowan Atkinson (their cultural attache).
There is one of boiler manufacturer that does just that and uses waste pipe can`t remember which one though seen it years ago, Not saying you should though.
Most condensing flue pipe is MuPVC which has a higher heat resistance. You would also want to be sure the seals could resist the acidic condensate.

Crikey, if you got the boilers for nought how tight are you :eek: Buy the proper flue!
"....and the property is not in France bit is in Holland.

Ah so I was close..ish ;)

When the boilers are presented to the test house for type approval they will be tested under all conditions with the approved flue. Connecting anything else would invalidate the approval. In the UK that would be illegal and is likley to be similar in Holland where I imagine the industry and installer base is leaques above us over here.

Looking at the manual (that now appears not to be the exact model) it does show 2 boilers connected to a single flue duct (drawing air from lower level)...a C83 flue setup. That would nearly halve the cost of the flue. Of cost fitting a rigid flue pipe down an existing chimney may not be easy (how do you support it and again is it approved for this application since you can't readily inspect it.)

Can you not relocate the boilers or just knock up an outside boiler house?

Keston boilers (that have had issues) always boasted that ordinary 50mm waste pipe could be used. This led to the "wrong" pipe being used. However even Modified uPVC has a marginal upper heat limit. Most proprietry flues are made from polypropylene that will cope with considerably higher temperatures (but it has to incorporate pushfit joints).

The ideal pipe would be Chlorinated PVC since it has a high heat limit and can be solvent welded. Unfortunately due to its licensing agreements and very few manufacturers it's hideously expensive.

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