Condensing boiler with shared flue?

26 Oct 2008
Reaction score
United Kingdom
Hi again,

I'm starting a new thread from an old one as my original query was answered (thanks!) and now I have a new query.

My current gas boiler is on its last legs. Ideally, I don't want put in an electric, as it will need a tank. I live in a block of flats with a shared duct, I'm not sure which type of shared duct, but I was thold that it was big. I would like to install a condensing boiler due to the efficiency.

My problem with this is the flue. From what I garnered from this forum, a condensing boiler needs pure air, which can't be obtained from the shared flue as it would contains poc's from other boilers?

One option was to run the flue 5m out the nearest external wall. However this would require a 40cm drop. And as the boiler cupboard is right next to the hallway I would have a 40cm thing hanging down as soon as I walk in. The other option was to put the boiler on an external wall which was either in the bedroom or living room. A big no.

I know I can drop a flue down from the chimney, but the block of flats is managed and the company that manages it are quite anal and are worried about damage to the roof and other peoples properties.

I understand fom the wiki // that flues have to be balanced to cope with gusts etc. So I was wondering about forced / fan assisted flues in some sort of twin flue arrangement. Could I run a straight horizontal pipe to the outside with a fan to take in air and then vent the flue via a different route to the shared flue? Or am I misunderstanding the purpose of a fanned flue (i.e. to provide a reliable airflow)?

Am I way of base with this idea?
If no, are they any decent boilers for this configuration?
Anyone with a similar problem?


Sponsored Links
Condensers can be used with shared flues and there are a number of manufacturers catering for this market.

But it is a case of the freeholder making the expensive changes to the SE Duct to make it compatible. I can't see them doing this for just one flat.
Wow! Thanks simond, you answered both my posts.

I guess it's electric then.

Thanks again,

Sponsored Links
Unforunately, the only external walls are in the lounge or the bedroom. But who wants a boiler in either place?
It's noisy and would dump significant heat into the bedroom.
The amount of heat released from a modern boiler is negligible and as mogget says turn it off at night and if it's a combi make sure it's possible to turn off the pre heat.
I install worcesters and you can barely hear them. also more heat coming of the pipes than from the boiler itself; if you box them in, you could not tell if they were on or off if your llife depended on it.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links