How to seal off a tricky chimney draft?

[brrrrrrr]

I have a decorative fireplace in my rented flat, (no actual heating just a metal cover) and behind it a large (pretty cavernous) stone space that leads up to the chimney. I want to block it up, as a lot of cold air is coming down (and heat escaping up) but am finding it difficult. I bought a chimney balloon but found it basically impossible to put it in position. The narrow bit of the chimney that I'd want to block up is about 2 metres from the ground, and it's hard to access via the narrow opening in the fireplace. (about 50cm wide)
Is there a way to block off the chimney without removing the decorative fireplace, mantelpiece etc?
I'd be happy to improvise with papers, old fabric etc - it's just a question of reaching up high enough. I've tried using a long broom but still couldn't manage! Any tips gratefully received.

 

[joni os]

Rock wool insulation enclosed in a bin liner can normally be persuaded to close off most chimneys

 

[Unregistered]

thanks joni - much appreciated, i shall investigate that.
the only problem is how to actually get the stuff into the narrow bit of chimney... it's proving damn difficult! i am trying to avoid taking the whole front off the fireplace, but at the moment i've got a small gap to fit things through (around 50cm wide) then a 2m high gap to reach across to stuff anything into the neck of the chimney - has anyone encountered this kind of thing before, and does anyone have any tips?

 

[lame plumber]

shouldnt block an old chimmney, it will cause damp problems and damage in the long run. fyi you must have the only chimney in the county that sucks air down!!!!

 

[PhoenixServices]

If you close it off you need to provide a vent in the chimney to allow it to breathe. Maybe look at having it professionally capped off.

 

[plumben]

As above a chimney needs to have ventilation to stop any damp forming, ideally you should have it capped at the top with a vent in the side at the top and a vent in the bottom

 

[Allgoode]

As above you can get some good vent cowls that with help ventilate the chimney without the incumbent problems of downdraughts.
Also a bit of boarding behind the decorative fire with a vent grill would help with the ventilation of the chimney.
Hope this helps,
Andy