On 16 Feb 2007 17:10:57 -0800, wrote:


wrote:
The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

http://healthandenergy.com/backdrafting_of_chimneys.htm

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.


I saw a house on TV a while back that had this problem and I think the
solution was to install a small fan made for this purpose on the top
of the chimney.

Restaurants sometimes use this type of fan for safety reasons, but it
will definitely create a upward draft.