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?

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

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.

Redeye wrote:
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?

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)

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.