Managed to get my chimney sheep up the chimney. Not easy as I have to reach behind the protruding hood & narrow opening, and it is a bit squished as I couldn’t get it all the way up, but it now provides a solid block and I can’t believe how much warmer the whole downstairs is. Previously the room with the chimney was always much colder since it faced north as well. Even secondary glazing didn’t help all that much, nor the foil insulation sheet behind radiator and also in front of the damper we had put in, but now it is almost as warm as back of house! Very impressed. Wish I’d bought it 10 years ago (but maybe you weren’t around then!) Only problem will be getting it in and out when we have the occasional real fire, but I suspect practice will make perfect.