The Stack Effect & Your Chimney

The Stack Effect:  Also called the Chimney Effect.  It refers to the movement of air into and out of buildings, chimneys, etc.  Indoor air density is different from outdoor air density, and this causes either a positive or negative buoyancy force.  It helps with natural ventilation and infiltration.

The Stack Effect and Your Chimney:  Drastically different temperatures between outside air and gases inside a chimney create a strong Stack Effect.

Your basement is the lowest point in your home, making it the most susceptible to issues caused by The Stack Effect.  Issues may include back drafting.

Prevent back drafting and improve chimney flow by opening a basement widow.  This will cause the Neutral Pressure Plane to move to the basement level, which reduces or eliminates negative pressure.

Do You Have Negative Air Pressure?

Here are some simple suggestions to test if you have negative air pressure (before lighting a fire in your fireplace).  Please always use caution!

1.  Open the damper on your chimney.  Hold your hand inside the fire box, near the damper.  Do you feel cold air coming down the chimney?

2.  Light a piece of paper and hold it in the same postition.  Did the fire go out?  Did air blown the flames down?

If you answered yes, you have negative air pressure.

Open a window or door to balance the air pressure in the room, and try the two suggestions again.  The flames will be drawn up the chimney if the air pressure has been equalized.

Symptoms Caused by The Stack Effect

Negative air pressure can cause the following:

  • Chimney flow reversal
  • Inability to light a fire
  • Weak, unreliable draft
  • Excessive smoking (when loading door is open)
  • People feel ill when inside your home (and better when outside)
  • CO is detected in your home

Can We Do Anything?

Yes!  There are products available to equalize the pressure and feed fresh air to your fireplace and other fuel-burning appliances.  There is hope!

To learn more, the CSIA Certified Chimney Sweeps at Doctor Flue, inc. can provide you with information.  We’ll help you find the right solution for your house and budget.

Call us today at 1-800-GET-FLUE or visit us online at

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