100cm2 ducting to outside required - any ideas ?

[mikej2005]

My mother-in-law has a floor-standing Worcester Bosch combi in an airing cupboard.

The installation instructions require a 100cm2 duct to be installed from the adjacent room (a landing in this case) to the outside and she only currently has a cylindrical duct with a diameter of 10cm2 (ie. 78.5cm2)

She has the boiler on an annual British Gas contract and the last time they serviced it, they hung an advisory notice on it and told her that the current vent didn't meet the minimum specs required, so would need to be changed.

I can only seem to find ducting of the type she already has or smaller, so can anyone point me towards a suitable duct, with internal and external covers, that will meet that 100cm2 requirement ?

Seems like a lot of hassle to go through to gain an extra 22cm2 of ventilation, particularly on a landing which is open to the downstairs hallway and pretty much the whole house. The vent covers aren't allowed to be closable either, so she's going to have one hell of a drafty landing once this has been sorted, that's for sure !

I guess this is just a consequence of having an older combi of this type ?

 

[JohnD]

you could put a second 100mm duct in (or add a smaller one) which might be easiest.

Or use 6" pipe instead of the 4" pipe you currently have

My mother has two 100mm vents in her boiler cupboard, one higher than the other, so I suppose it gets a bit of convection.

I don't know if you could ventilate the boiler cupboard rather than the landing, like this. If so, you could draughtproof the airing cupboard door and pipe-holes in the floor and ceiling so the cold air does not blow into the rest of the house.

I should think it will be pretty good for drying clothes in there.

 

[mikej2005]

I don't know if you could ventilate the boiler cupboard rather than the landing, like this. If so, you could draughtproof the airing cupboard door and pipe-holes in the floor and ceiling so the cold air does not blow into the rest of the house.

Unfortunately not - the airing cupboard doesn't have any external walls and requires two huge vents itself - a top one of 200cm2+ and a bottom one of almost 500cm2 !

Sorting out vents large enough for that has been a nightmare, as the ratings for even the larger square vents commonly available are actually a lot lower than they appear.

This external vent is the last thing I need to sort. Are 6" vent covers fairly easy to get hold of ? I've only seen 4" so far.

 

[JohnD]

I haven't got any myself, but 6" extractors is the next size up from 4", so I would though they were available. You may need to contact someone in the ventilation/extraction trade.

 

[twgas]

exactly what model is your mum-in-law's boiler, so that correct advise will be given

 

[mikej2005]

exactly what model is your mum-in-law's boiler, so that correct advise will be given

Sorry, I didn't have the model number to hand when I posted the message - it's a Worcester Highflow 3.5 (or 4.5) BF, OF or RSF, according to the manual.

I'm not familiar with the different types of flue, but it goes out the top of the boiler into the loft and up through the roof. The ventillation to the airing cupboard is required as stated above - one smaller high-level vent and one larger, low-level vent, plus this additional ventilation to outside if the airing cupboard opens into a room (British Gas, in this case, are not differentiating between a landing and a room)

 

[Gasguru]

You will find the manuals in the installer section on the Worcester site.

However on the likely basis that the boiler is of 29.6 Kw gross the required ventillation would mean a the top vent of 270cm and lower vent of 542cm and an external vent of just over 100 cm.

It would appear your existing compartment vents are undersized. From the 1st June this year the ventillation standards are being tightened up and for most installations that means they will have to have perfectly sized vents (since you are really only allowed 1 minor fault on ventillation and flueing with open flued appliances). It is common to have a minor fault with the flue installation..hence ventillation has to be perfect, otherwise the fault category has to be upgraded ie appliance not to be used.

The existing wall vent is undersized...the easiest way would be to increase the diameter with a 127mm core drill. You can then fit a purpose designed core vent from Stadium (or others). They are available from merchants.

As for the compartment it is normal to dispense with individual vents and have a louvre door instead with the Kw sized boiler you have.

I would also advise you fit a carbon monoxide alarm (not a spot detector) the hallway due to the proximity of the bedrooms.

 

[mikej2005]

Thanks for the comments. To answer a few of your points :

WB have manuals for many of the Highflow models, but not the 3.5/4.5 unfortunately. Luckily, the mother-in-law does have one however - I just don't have one to hand here.

Your vent figures are spot on - I used two vents for the lower opening, so that one is fine and the top one is within a few cms of the required value. Louvre doors would be an option I guess.

She does have a CO alarm on the landing.

I'll look into the external vent suggestions.

Cheers.

 

[petit_pablo]

If BG have told you it needs upgrading then did they not leave a quote for a core vent to be put it that would provide 100cm2

 

[mikej2005]

If BG have told you it needs upgrading then did they not leave a quote for a core vent to be put it that would provide 100cm2

No they didn't, but I'm more than capable of doing the work myself - I'm just trying to suss the options and source the materials.