Q: We just had our fireplace cleaned and the cracks sealed, but still sometimes have a backdraft problem where the smoke doesn’t go up. There’s no flue on the chimney. Any idea how to stop this?
A: Chimneys operate on the basic law of physics, which is: Heat rises. When the inside of the chimney gets hot, the rate of the upward draft will increase as well. If the backdraft only happens when the fire is first lit, then the problem may correct itself as the inside of the chimney gets warmer. When lighting the fire, use newspaper and small kindling to produce a high flame to raise the chimney temperature faster and jump-start the draft effect.
Also, you may need a combustion air source to help maintain the draft. Try partially opening a window in the same room as the fireplace. Also, make sure no exhaust fans (kitchen or bath) are running in the house while you have a fire.
There’s also a correlation between the diameter of the flue opening and the height of the chimney. The larger the flue diameter, the taller the chimney should be to ensure a good draft. If the backdraft is still a problem after the chimney has had time to heat up, then you may need to add an extension on the top of the chimney to increase the draft.