Why can't I extend my boiler flue?

[Richard J.]

In our terraced house, we have a Ferroli Modena 102 combi in the kitchen, with a horizontal 100mm concentric flue of 0.5m length, ending on the outside wall which at that point is part of a single-storey extension to our house. Unfortunately, it's rather close to next door's kitchen door and patio, and the smell of the initial exhaust when the boiler starts up is quite noticeable.

According to the manufacturer's manual, the maximum flue length is 4m, but any bend counts as 1m, so a horizontal flue like mine, attached to the top of the boiler by a 90deg bend, has a maximum length of 3m, after the bend.

Fine, I thought, I can add a 90deg bend where the flue emerges from the wall, and then a 1.5m concentric flue going vertically upwards to end about half a metre above the top of the wall. That would be an effective length of 0.5 (existing) + 1 (new bend) + 1.5 (new flue) = 3m. But my local Corgi-registered plumber says that you can't mix horizontal and vertical flues in this way, and he says Ferroli confirmed this to him. The only answer would be a new vertical flue system which would have to pass through the existing flat roof, which I am reluctant to do.

If the boiler will accept either horizontal or vertical flues, why can't you mix them?

[John Stumbles]

Ask Ferroli: it depends what they specify for your boiler. There isn't any fundamental rule against mixing horizontal and vertical runs of a balanced flue (and I'm a bit surprised if they say you can't) but the manufacturer's instructions are effectively law in this matter. Might be worth checking with them for yourself: it should be in the installation manual which you should have (if it's also the service manual). If not you should be able to get one from them, either online or by phoning them. Or there may be a separate manual covering flueing options, which you should also be able to get from them.

[Christian McArdle]

That's up to what Ferroli will allow. I have a mixed vertical/horizontal flue system on my Worcester Bosch Greenstar. Although no mention was made of this configuration in the installation instructions, it was pretty obvious through extrapolation what the performance would be and a call to their technical helpline confirmed that they could see no reason not to install such a system.

In my case it started with the horizontal turret of the horizontal system, about 1m length, then a 90 degree bend upwards into the vertical terminal through the roof.

I suspect that your proposed solution would be just fine, but you mustn't install something that the manufacturer forbids. There may be some incompatibility that isn't apparent to you.

Christian.

[fred]

In article , Richard J. writes

I don't see anything wrong with what you suggest and it would appear that ferroli don't either: If you take a look at the ferroli website & go to the Modena page, then to Flueing, there is a picture of possible configurations on the bottom left. The two lowest and leftmost boilers in that picture have

2x90deg bends with vertical exit (although they don't go above the roofline) and second from right in the top storey has 2x45deg bends and goes through the roof. If 2x90 is indeed off limits, then 2x45 and a slant opening in your wall sounds like it would work.

Could be your guy is telling or being told porkies. Try to talk to someone at frerroli to clarify the situation, if no joy then print the pic & show to your corgi (silly snappy dogs, never liked tem ;-).

[John]

configurations

Quite possibly you can do what you suggest but the normal wall type flue terminal packed in the boiler kit will not be suitable and you will need a vertical terminal. The proximity to the eaves will be a considerable factor affecting the suitability so as others said talk to Ferroli and maybe fax them a dimensioned sketch of your proposal

[Richard J.]

Thanks for all your advice. I e-mailed Ferroli last night with a sketch of what I wanted to do, and got a reply this morning saying it *was* acceptable. Must have been a misunderstanding somewhere when my Corgi spoke to them.

[fred]

In article , Richard J. writes

Good news, thanks for feeding back.