Opening a chimney breast

10 Nov 2015
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United Kingdom
Hi all,

I have planned on opening up an old fire place to install a gas oven in a chimney breast and blocking it up above. I haven't planned on adding an extractor as there is a vent in the corner where I can fit an extractor fan.


No lintel can be seen on found above the mini lintel at the opening. I plan on adding a concrete lintel at about 1.6m using acrow strongboys.

The chimney breast is 1.4m, I had planned on a minimum of 150mm on each side for bedding. As such I had planned on having a brick length on each side so 1400 - (215*2) gives me a total opening of 960mm. Is it sufficient to have a 65mm cut down brick each side of the lintel?

Can I have the lintel spanning the entire length of the breast without the cut brick on each side? Or should I consider having a smaller opening?

Any ideas or comments on things I haven't considered would be much appreciated.



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1. Your lintel should typically be installed at 1.7m to 1.8m height from hearth level to underside of the lintel.

2. What are the Mfr's installation dimensions for the gas oven ie. the width of the building opening required?

3. What does the Mfr's instructions say about extraction? Extraction ducting must be planned in advance esp. the terminal.

4. Do you intend to install any other appliance or a unit or fixture in the opening?

5. A gas supply will be needed - a GSI will also be needed for any gas appliance. Plan the gas pipe run.
An elec supply is needed - safety zones must me kept to.

6. When you open up you must remove all soot from the fireplace and have the flue swept.

7. A vent must be fixed thro the chimney breast into the flue - there must also be a vent at the stack terminal.

8. "a vent in the corner" what do you mean?

9. Use a plate or backer board to cover the flue opening at the lintel. The flue vent must be installed just above the plate.

10. Carefully examine the c/b and its return walls for any signs of dampness.
Hi Ree,

Thanks for the reply

  1. I had planned on installing the lintel at about 1.8m (1.6 apr' being the clearance height).
  2. The instructions say that the oven must have 75mm clearance on each side from the top of the burners and 650mm from the top. It stands at max 930mm so height should be ok. I have looked at narrower cookers as a 900mm may be to tight.
  3. I hadn't planned on installing any other appliance in the opening apart from a light fitted above.
  4. A gas supply is already fitted to the base, I assume a gas heater was there before. This I will get moved to a more suitable position by a GSI reg' human prior to starting any work higher up. It requires 13 amp 240v plug socket which I happy to do as I am adding more sockets in the kitchen.
  5. The instructions say that it doesn't need direct ventilation if the rooms is over 11m cubed (which it is), only a window that can open. The vent is a terracotter stile vent fitted on to the external wall.
  6. I shall have the flue swept, are air bricks installed above the lintel suitable for flue ventilation? Ventilation is already present at the stack.
  7. What do you mean by c/b?
Thanks again for the help, if you have anything that you would check prior to any work I would be happy to hear them or any other recommendations.
Much appreciated
So, you are talking about installing a free standing cooker with a gas hob - is that right?

Dont do any first fixing of elec or gas etc until you have finished the brickwork & flue details.

I still dont know how wide the actual appliance is?

A name & ref number for the cooker would help?

"a vent in the corner" means what? Dont use air bricks - a 9" x 3" hit and miss surface vent will do.

You could use a re-circulation hood (c/w lights) but height above hob comes into play.

Could you make & scan a rough sketch (with dimensions) of what you propose?

chimney breast.
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chimney breast plan.jpg
Hi Ree

Yes a free standing gas cooker with hob.

Looking at cookmaster CK90 hob or Rangemaster 60cm 10732, based on my drawings I should have enough room for the CK90.

The "vent in the corner" is louvred vent fitted to external wall.

I had considered a re-circ but I don't see much benefit from it for the additional cost, difficulty in installation and problems with clearance from the hobs.

Thanks again.
Thanks for the diagram - its much clearer than the average contribution.

Believe me, extractors are almost a necessity above a hob, esp in an isolated cooker position.

Apparently you dont have any other elec/mech extractor in the kitchen. You should have one fitted esp. if you are doing up the kitchen.

The lintel can be raised - the significant dimension is 760mm above the hob to the extractor or any bridging. This can be fudged a little.
I'm sure you appreciate that the cooker will project from the face of the c/breast.

Given the built-in advantages of a re-circ extractor, the cheap prices, & the ease of installation its definitely worthwhile.

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