Ohhhh the draught !

[Davey]

So, what was the decision?

[Rick]

why not build in a steel 'trap door' across chimney ... closed when fire not in use.

But as others point out you should have updraught .. not down. You must have a hell of a leakage of air elsewhere that is causing the

-ve pressure. Do you have a non balanced boiler, or non room sealed gas fire somewhere ?

[Davey]

Why go to that bother and expense?

No and no, but: The house is several hundred years old, and has lots of leaks and nooks and crannies and underfloor gaps, and a cellar. Take your pick! Also, the local prevailing wind goes along the house from one end to the other, acting as a venturi between us and the house opposite, only a few yards away. The negative effect in the room with the chimney is reduced considerably if we close the door to the adjoining study. Sorry you asked?