Flues, flues and flues. Combi boiler flue through chimney?

[BFG]

We have a 1930's house with two chimney bre@sts. Downstairs only have openings. In the front room, there is a back boiler and gas fire, in the kitchen there is a gas fire.

Now, I will take some fairly advanced DIY jobs, but don't know too much about gas appliances, and safety is an issue.

We will replace the back boiler with a combi boiler. I have an idea to mount it in the loft (done it before), however, we don't have a roof with a pine end, so I either have to take the flue out through the roof tiles, or I can mount it on the chimney bre@st and take the flue into the stack. If this is possible in itself, this brings me on to a flue question.

Which brings me to my first question: If I have a combi in the loft, and a gas fire in the front room, both venting into one stack, I presume I need two liners. Or can I join them some how? If I need two, are shaped sections available to allow two flue liners to vent through one chimney pot?

The second question: In the kitchen, we want to replace the gas fire with a real fire. Wood and coal burning. What shouls I do with the flue? I guess it will have a flue liner, being gas. Can I use that with a real fire? Or do I need something else?

Any advice greatly appreciated.

 

[breezer]

I am not a plumber or heating engineer (or C.O.R.G.I registered for that matter)

I was curious to know the answer to your question and i found this

http://www.fp.rdg.ac.uk/wkc1/DIY/gas/msg00080.html

I particualy liked the bit that said "a DIY er in Plymouth decided to do some gas work and
> shortly afterwards there was a bit of a bang, well rather a large bang
> actually and it brought the house to the ground " and i also agree with "but in my humble opinion safety
> comes before cost, every time."


so I would say the answer to your question is get a professional in. Sorry

 

[ogoshi]

If your combi has a balanced flue or fanned flue then the answer is no,you cant vent it into the stack.You must get a corgi registered installer to install your boiler for legal safety reasons

 

[breezer]

I also remember seeing a programme....... and it showed how a balanced flue works. The inner part of the flue is longer than the outer part. As
the hot exaust gasses are under pressure they "shoot out" through the inner part of the flue to free air. As this happens cold fresh air is drawn in through the outer (shorter) part of the flue at the same rate as those of the gasses going out.

So if you were to look at a cross section of a flue you would see gasses going out as fast as air comes in, that is why it is called a "balanced flue"

so that is why a balanced flue is always on an outside wall, so if you put one in a small space it would suck back its own exhaust gasses.

Just thought i would mention it.

 

[amtodd]

Have had similar problems before so have an expert's opinion (not mine):-

According to my favorite plumber he can put a flue liner up a chimney stack for a gas fire, but if the flue is sound - and it needs to be checked by a CORGI registered plumber - it may not need one. If the stack leaks gases into other rooms /loft it may well need to be lined.

However a flue can't be swept properly, so if a solid fuel fire is what you want, you'll need to remove the liner if there is one, and have a smoke bomb test carried out. - renewing the morter on the brickwork will fix stop smoke in the loft.

Removing a liner doesn't need a plumber and can be lots of fun if you like demolishing things. Disconnect the cowl and fixings at the chimney pot and hey presto the lining - complete with accumulated soot and debris - will be in your fire place. If you forget to cover up the fire place, the lining will be there, but the soot and debris will be all over the house.

For a combi boiler in the loft he could put a balanced flue up a chimney stack to terminate in outside air. However the balanced flue can't stop inside the stack nor too close to windows etc., nor join with another flue, balanced or otherwise.

 

[BFG]

If you forget to cover up the fire place, the lining will be there, but the soot and debris will be all over the house.

Many thanks to everyone for your replies - very useful.