Thermal siphoning is when smoke is carried up and out of the chimney and pulled directly back down by a neighboring flue. The natural tendency of heat to rise may explain this common problem. The warm air inside and cold air outside creates a form of draft inside the home. The warm air, or high pressure area (positive), will be on the upper levels with cooler, low pressure areas (negative), at the lower or basement levels. The negative pressure area draws in outside air trying to reach that neutral plane and can do so by pulling from the chimney. This is called stack effect.
Opening a window in the dead of winter is not an option, so what do you do? A top sealing damper could help! A top sealing damper would sit on top of the basement fireplace flue sealing it off from the top when not in use.
Call or contact Boston’s Best Chimney today for an evaluation and start enjoying that fireplace with no worries!
(note: this does not solve smoke transfer issues through cracks of flues)