chimney effect

chimney effect

The chimney effect, also known as the stack effect, is the tendency of heated air or gas to rise in a duct or other vertical passage, as in a chimney, small enclosure, or building, due to its lower density compared to the surrounding air or gas.


The presence a chimney enhances the effect for several reasons:


  • The lower effective section increases the air speed in the chimney; this lowers the pressure in the chimney, creating a greater difference in pressure with the rest of the interior space, thus accelerating the air movement (Venturi effect).

  • Being tall, the chimney increases the temperature difference between the air intake and exhaust points, increasing the Venturi effect.

  • Even a slight wind lowers the pressure at the chimney exhaust, and consequently increases the efficiency of air extraction.