Insulation in unused fireplace?

[Chud]

Hopefully someone can answer this:

1930's build house, we've got an unused fireplace in our lounge, it obviously had a gas fire in there at some point as there's an aluminium flex flu coming down into the fireplace and a register plate about a foot above the opening.

We plan to line the fireplace and put shelves in it for DVD player, sky box etc. I'm going to line the top to stop dust etc raining down the chimney onto the electronics - that top lining will obviously need to have a vent in it to ventilate the chimney but can I put a layer of earthwool etc between the lining and the register to damp down the airflow to prevent actual draughts or am I just going to create condensation issues in the insulation?

 

[John D v2.0]

Not totally sure, but your draught would mostly be upwards because your room will be warmer than outside so the buoyancy will push the air upwards.
You need ventilation to disperse any condensation but you also need to make sure the chimney is capped and no water coming down in the rain.