Reducing draught from vent behind fireplace

Hi

What is best for boarding up behind my electric fire, there is a big draught coming through the fireplace from an air brick in the chimney just behind the fire place

Could I just use celotex or plasterboard to board up
Just behind the electric fire reducing the draught but yet still allowing air flow in the chimney

Or should I just silicone up some of the holes in the air brick to reduce air flow perhaps by 50%?

That looks like a Baxi installation, it will have air vents going into that sunken box. Fill the box with some thing, bricks and sand, soil? The other thing to do (anyway) is to seal the bottom of the flue which is a huge hole going up to your chimney pot, just leave a 1" diameter hole in the sealing.
Frank

Hi

It is a baxi it says on it, we have no chimney as we took it down, which is why we put a vent in the outside chimney stack just below where the baxi is for airflow

How do you open the box and why fill with sand?

Is it ok to board behind the electric fire to reduce the draught coming in?

The air brick should be installed above the Baxi unit.
Did you drop the chimney stack but the "outside chimney breast" is still in place? Is the flue vented at the top? Has it been swept?

If you want to cover the "box" then simply lay, and silicone seal, a board of some kind over the floor ventilation draught "box" - perhaps foam around the cables.

Behind the elec fire you could build a simple frame and cover it with a piece of plaster board. Seal off the opening completely - just so long as the air brick is providing thro ventilation up the flue.

Tale about a Baxi burner:- I bought a traditional stone cottage, the one living room had a 1970s coal burning fire in it and a very smooth red floor. There was a little hole in this red compound and some marks where it had been patched up. Curiosity got the better of me, so I inserted a bolster under the open edge of this red compound and lifted it, it came away in almost a room sized sheet and underneath there were traditional flagstones. Great I thought. Got rid of the red stuff, only to find in the centre of the room about a yard away from the fire was a concrete square, the hole in the red stuff had been by the side of it. To my amazement, some one had cut the square out about 18" square in the original flags, then cut TWO trenches through the flags to the outside wall and a third trench to the fire. When the trenches had been excavated, there was a 3" air pipe in each one, the shortest one going into the front of the deep Baxi grate. The builder had manged to cut through and ruin 18 3' X 2' flags.
Hence I found out that the Baxi grate boxes have an air vent in their front face!!
Frank

Hi

Yes the chimney stack has been dropped but the outside chimney breast is still in place and is vented at the top.

All I wanted to do is cover the whole behind the fire so it eliminates any cold air draughts coming in. Based on my pictures above would you just attach plasterboard or kingspan to a frame around the opening inside the fireplace which would still enable the ventilation from the air brick and up the chimney yet reducing the draught into the living room.

Just out of interest if I boarded over the grate which has been removed, would I still get ventilation up the chimney via the baxi boiler?

Yes, you must do something about both the sources of ventiltion, the under floor one can be closed of completely. The chimney stack should really be capped and have a small vent at the top and the bottom end should also be blocked off with a small hole 1" diam in it. This is so any water that penetrated the sides of the stack will be dried out by a small air current.
Leaving the baxi grate unsealed will result in air blowing in or out of it, depending on the direction of the wind on your house. When you have a roaring coal fire the hot gases going up the chimney always suck the baxi air upwards under the fire.
Frank

Hi frank

The chimney cannot be capped as it has been taken down to roof level and covered with roof tiles, but it is vented at the top

At the bottom of the chimney stack there used to be a pull out grate so you could empty the ashes outside the home, this has been removed and bricked up but with an air brick installed, but this is causing the draught through the electric fire

How do I seal the baxi?

I was also going to cost the stack the Thomson water seal

My friday post indicated exactly what you must do - talk about taking a horse to water.