Non-balanced flues & extractor fans

[Redeye]

Amongst the many other "features" of the 250 year old house we moved into 4 months ago is a worsening condensation problem. I've got an extractor fan ready to fit in the kitchen window as stage 1 of my attempts to increase ventilation. However, the window I need to put the fan into is right next to the boiler which I have a horrible feeling has a non-balanced flue (a Vokera Excell 80SP).

This appears to be quite a bad thing. However, if I put an air vent in the window at the other end of the kitchen would I still be okay and avoid a bout of carbon monoxide poisoning?

Also, the boiler is about to be replaced, most likely with a Worcester-Bosch. Does anyone know if these normally have balanced flues?

[Christian McArdle]

Yes. It will almost certainly have room sealed fanned flue, unless you have found a seriously Luddite plumber with a supply of ancient illegal boilers. Quite frankly, wait until it is in before commissioning the extractor.

Christian.

[Phil L]

In theory, the extractor should draw air in through the vent that you intend fitting, in practice however this isn't going to work. The first thing to note is that your ex-fan is going to shift XX litres of air per minute, if the vent you install cannot allow this much air or greater to flow inwards, there's a possibility that you will draw exhaust fumes from the boiler...what kind of 'window vent' were you thinking of? - if it's one of those trickle vents then forget it - I'd suggest a 9 X 6 inch

*plastic* vent fitted into a wall, this will give you 100mm2 of free air flow, which /may/ be enough air flow, provided there are no obstructions either indoors or out, personally, I wouldn't risk it at all until your balanced flue is installed. (yes, WB boilers are balanced)

[Redeye]

Thanks for the advice. Further investigation has muddied the waters a little.

The flue on the current boiler seems to be fan assisted which would appear to make it a little less risky to have the extractor fan working too.

The suggestion of having an air brick or vent in the wall is a good one but unfortunatelt a bit impractical as the walls are 2 foot thick and made of stone. This is why I was thinking of putting a vent in the window at the other end as the inlet instead. I haven't really managed to find what I'm looking for yet - what I really want is a vent to act like an air brick to fit in a single glazed window pane.