draft coming from old fireplace

[qwertyjjj]

Tis fireplace used to be a traditional fireplace with a damper that was broken - not sure if it was stuck open or it fell out but either way it's open now permanently.
It was replaced about 10 years ago with a slow combustion fireplace but there is a draft coming through the holes in the brick.
The air now comes in through the top of the new combustion burner so can I just block up the holes? The brick is not sold anymore so I am not sure what material to block up the holes with?

https://docs.google.com/file/d/0BwSNadx1dbgxSHBJeTFBQTFyRDg/edit?usp=docslist_api

Holes on the bottom have a draft coming through.
The top ones seem find but must connect to the same cavity behind somewhere.

 

[DAKSY]

The draft is convection air. Warm air is entering the upper heatilator vents, cooling
& dropping thru the masonry & exiting from the lower ones.
You will feel this as a cold air flow.
The best way to eliminate this problem is to keep a fire burning in the insert.
That will keep the entire masonry construction warm.
You can probably block the heatilator vents with a masonry cement mix..

 

[qwertyjjj]

The draft is convection air. Warm air is entering the upper heatilator vents, cooling
& dropping thru the masonry & exiting from the lower ones.
You will feel this as a cold air flow.
The best way to eliminate this problem is to keep a fire burning in the insert.
That will keep the entire masonry construction warm.
You can probably block the heatilator vents with a masonry cement mix..

The fire is only on occasionally though. I am not sure if for the new slow burner, that they inserted another chimney inside the brick chimney or if they used the existing one.
The top vent holes are only a couple of feet above, would enough warm air get in there even when the fire is not on?
The bricks in the holes have smaller vent holes (sideways on, you can;t see them in the picture) so I can probably block those up but do I have to block all 4 vents...top and bottom?

 

[DAKSY]

Block the bottom ones& see how that works. If you start to get a cold draft from the top ones, block them too

 

[qwertyjjj]

Block the bottom ones& see how that works. If you start to get a cold draft from the top ones, block them too

I should add that the slow burner has a fan but I think the air must be coming in through the sides of the burner and or down the window as that seems to be how it gets air.
Unlikely that it's liked to those vent holes at all?

 

[DAKSY]

Very unlikely.

 

[qwertyjjj]

Very unlikely.

There is also a hole on the outside of the building about 6 feet to the left of the fireplace. I cannot work out what that is for.
It doesn't seem to connect to the vents (at least no sound goes through) but it looks just like some type of vent...it is about 2-3 inches.

 

[DAKSY]

Not a clue. Could be anything. Got a pic?