Gas Fire ventilation

[Disk]

I understand that a room containing a gas fire with an input greater than 7KW requires additional ventilation of 5sq.cm for every kw over 7kw.
Does the size of the room not have a bearing on the amount of additional ventilation required?
Instead of using an 'airbrick' through the cavity wall, is a grille in the internal door to the room (which leads into the hall and stairwell and does not contain ano gas appliance) a suitable means of providing the additional ventilation?

 

[chrishutt]

Does the size of the room not have a bearing on the amount of additional ventilation required?

No. Why should it? Ventilation must be to outside, either directly or indirectly (via other rooms), but ventilation must comply to British Standards and/or manufacturers instructions.

 

[ollski]

I understand that a room containing a gas fire with an input greater than 7KW requires additional ventilation of 5sq.cm for every kw over 7kw.
Does the size of the room not have a bearing on the amount of additional ventilation required?
Instead of using an 'airbrick' through the cavity wall, is a grille in the internal door to the room (which leads into the hall and stairwell and does not contain ano gas appliance) a suitable means of providing the additional ventilation?

Usually, though not always, a gas fire exceeding 7kw will require 100 cm2 of ventilation, but depends on the requirements in the manufacturers instructions. The vent must communicate with outside air eventually and if there are 2 or more internal vents on the way to the outside vent each one must be 50% bigger than the requirement.

 

[PEDANTICVINDICTIVEMAN]

Depends on the fire, floor vent ok as long as floor ventilation adeqaute, but flueless fires have to have a vent in the wall, like at my house

 

[Disk]

Thanks for replies.
Whilst looking for the best place to fit a ventilator I have found that there is already a traditional clayware ventilator fitted low down in the cavity wall.
However the vent is only visible externally.
Internally the walls are dry lined with plasterboard and you cannot see the vent because it only extends to the face of the internal blockwork which is covered by the plasterboard, consequently there is a hell of a draught behind the plasterboard.
Is this what the vent is supposed to do (ie vent the back of the plasterboard) or should it have been carried through to the face of the plasterboard as a proper room ventilator? If so I can use it as the vent for the fire

 

[Gasman1015]

No, you cannot use that as the vent, if it is an air brick it is not the correct size.
You can buy a purpose made one such as a black hole.

 

[Disk]

If its not for fire ventilation then does anyone know the purpose of this airbrick?
It can't be to ventilate the gap between the plasterboard and inner block wall surely, this defeats the object of any insulation in the wall cavity.
If its not serving any useful purpose then it could be replaced with a Black Hole.

 

[Paul Barker]

Your asking us to use our chrystal balls.

We cannot comment on what your airbrick was for. It is quite obvious though this entails a little fortune telling, that the dry lining was done more recently than the airbrick was installed, and that the airbrick is no longer serving it's designed purpose.

 

[Disk]

Apologies, I didn't explain clearly enough.
The house was built 10-15years ago and in keeping with many houses then and now, was built from new with the all ground floor internal walls lined with plasterboard on plaster spots rather than a more traditional 2 wet coat plaster.
The air brick also looks like it was built in during construction.
I cannot fathom the air bricks purpose other than perhaps the builder did not finish it properly.

 

[ollski]

Apologies, I didn't explain clearly enough.
The house was built 10-15years ago and in keeping with many houses then and now, was built from new with the all ground floor internal walls lined with plasterboard on plaster spots rather than a more traditional 2 wet coat plaster.
The air brick also looks like it was built in during construction.
I cannot fathom the air bricks purpose other than perhaps the builder did not finish it properly.

Is it ventilation for the cavity under a suspended floor?

 

[Disk]

No, ground floor is concrete slab.

 

[Paul Barker]

I suspect the builder did not finish it properly. Maybe the air brick was an option and if not taken up it was dot and dabbed over?

Anyhow I've now forgotten what your requirements were. What do the fire manufacturer's instructions say? DFE's are quite hard to spot these days as oposed to ILFE's. On the whole ILFE's don't require ventilation and DFE's require 100cm squared (unless stated otherwise in manufacturer's instructions), whatever their net heat input. Because of which I find it's always best to go by manufacturer's instructions. If there is no mention I would check with the manufacturer as to how they class their fire. Of course if you ask ther girl on the switch whether it's a dfe she won't have a clue, but quaint fire manufacturer's girls act a bit like Doctors receptionists. You have to get past them first to get to the person with any knowledge or training.

 

[Disk]

Thanks for all responses, I will be fitting a 'Black Hole' vent giving 100sq cm free area.
However can someone tell me why BS5440 Part2 2000 requires a Free Area of 5sq cm for every 1KW input above 7KW, ie 35sq cm for a 14kw input fire, but everyone here and the manufacturer tells me to use 100sq cm?
Looking at the specs from Stadium Group plc who manufacture the 'Black Hole' vents, their products are based on the 5sq cm calculation ie a 70sq cm Effective Free Area vent is sufficient for a max 21KW input fire : (21-7)*5.

 

[ollski]

Thanks for all responses, I will be fitting a 'Black Hole' vent giving 100sq cm free area.
However can someone tell me why BS5440 Part2 2000 requires a Free Area of 5sq cm for every 1KW input above 7KW, ie 35sq cm for a 14kw input fire, but everyone here and the manufacturer tells me to use 100sq cm?
Looking at the specs from Stadium Group plc who manufacture the 'Black Hole' vents, their products are based on the 5sq cm calculation ie a 70sq cm Effective Free Area vent is sufficient for a max 21KW input fire : (21-7)*5.

BS 5440pt2 is to be used where there are no specific instructions from the manufacturer.
A dfe fire generally burns under an open 9x9 chimney and the flue is not guided, hence shifting a lot of air changes through the room which needs replacing.

 

[Paul Barker]

Yes, what the manuifacturer is telling you is that this is a dfe fire. They are a special case.

Actually you must fit into one of 3 categories to have a dfe fire.

1/ Ignorant of efficiencies
2/ the sort of person who wears contact lenses despite the pain (in other words care more about looks than performance)
3/ Stinking rich

Basically a dfe fire is like lighting a bunch of bunsen burners under the chimney.

Craisy government of ours wants to make our lifes hell over central heating boilers but you can float neat gas up your chimney as much as you like, and then ensure a draft whistles round the house through the required ventilation which has to be there whether the fire is on or off day and night 365 days a year.

Only reason domestic boilers in the UK have to meet tough criteria is because it's one tangible thing the government can control and makes them look good in the world stage.

Time they looked at electricity generating and the vanity of gas fire industry.