Venting old chimney stack/flues

[Cocat2517]

Hi
Property I bought has a fireplace in lounge and another in the bedroom with flues up to a chimney stack that has been dropped below roofline.

As far as I can tell the chimney is not ventilated at the top where it's been dropped. The fireplaces are still open so warm air from the house is going up the flues. I want to brick/board across the fireplaces to prevent heat loss, but I understand ventilation is required?

I'd prefer not to fit airbricks or plastic grills as heat and warm moist air will still escape up flues. Would drilling 3-4 holes (approx 12mm diameter) in the exterior wall through to the flue be ok to allow outside air to pass through into the flues to keep it all ventilated? I'd then fit louvre style grills with insect screen over the holes.

 

[foxhole]

If the chimney has been removed then there will be little air movement up a sealed stack .
Stick chimney balloons in the fireplace to seal .

 

[Cocat2517]

If the chimney has been removed then there will be little air movement up a sealed stack .
Stick chimney balloons in the fireplace to seal .

Yeah there's hardly any air movement, so I was going to drill some holes in exterior wall high up and put a vent, along with one at the bottom so air can enter from outside, travel up & out again to keep it ventilated.

If I put one of those balloons up there won't it stop airflow and cause problems with condensation on the internal walls? I thought you had to keep them ventilated?

 

[blup]

There are different schools of thought, some say there is no need for ventilation as there is no movement of air, others that pre existing conditions in the chimney from the tarry deposits when in use, require ventilation.

I believe technically building regs approval is needed when a chimney is dropped below roof line - on the adequacy of ventilation issue - so if you do introduce it be aware that you would need to satisfy the requirements if challenged.

Blup

 

[Cocat2517]

There are different schools of thought, some say there is no need for ventilation as there is no movement of air, others that pre existing conditions in the chimney from the tarry deposits when in use, require ventilation.

I believe technically building regs approval is needed when a chimney is dropped below roof line - on the adequacy of ventilation issue - so if you do introduce it be aware that you would need to satisfy the requirements if challenged.

Blup

Thanks, this was done I think about 10 years ago, long before I owned the place, so not sure how much involvement building had.

I've seen arguments for/against venting, but wanted to play it safe. So would vents fitted to the outside of flue too & bottom be ok, rather than fitting them inside?

 

[bobasd]

all the flues that gather at the top of the chimney breast might need sweeping.
all redundant flues need ventilating top and bottom.
no need for BCO then or now to be involved.

most dropped stacks are left open in the loft by lazy workers - place your hand on top to feel for an opening. if the top is sealed knock a brick out of the face of the loft chimney breast.

 

[foxhole]

Needs ventilation if it can get wet during rain as it can penetrate the stack . If there’s no air movement you can’t loose any heat ,

 

[Cocat2517]

Stack is closed off in the loft, can't find any air movement. I'm definitely going to ventilate to be on safe side. Question is can I ventilate from external wall only, or must add ventilation on internal wall too?

 

[blup]

It would seem to make sense to ventilate at the top of the stack, not the side, to maximise air flow, and at the bottom as well.

Blup

 

[bobasd]

OP, if the flues at the fireplaces are going to be blocked off then by all means install an external air brick at the bottom of each flue and an external air brick at the very top

 

[Cocat2517]

OP, if the flues at the fireplaces are going to be blocked off then by all means install an external air brick at the bottom of each flue and an external air brick at the very top

Thanks, this is what I wanted to do as I don't want internal vents that are unsightly and let out heat.

The walls are solid slate blocks, not bricks, so won't be able to fit airbricks as such, so was wondering if a few holes drilled through covered by a louvre vent plate would suffice?

 

[blup]

If you drill holes, drill on a downward angle to reduce/avoid rain entering.

Blup

 

[Cocat2517]

If you drill holes, drill on a downward angle to reduce/avoid rain entering.

Blup

Thanks, will do. It'll be covered with a louvre vent anyway, plus it's an East facing gable end with another house fairly close, so quite well sheltered.

Regarding drilling, the walls are made of very hard solid slate blocks and are 12 inches thick, just wondering if it's even possible for me to get through them. I've got a 400mm long masonry bit (12mm) and an SDS hammer drill.

 

[blup]

400mm should be long enough if there are no other obstructions, one way is to build up the hole sizes so each successive drill bit has less to remove.

I found Dewalt long length sds bits very good (through brick and block) but it's quite expensive buying the individual bits.

Blup

 

[foxhole]

You can buy 1m drill bits very cheap , handy to keep .
https://www.toolstation.com/sds-plu...MIiuXmmNyg5AIVTLDtCh2DIwgWEAQYAyABEgI10_D_BwE