Why does chimney height matter?

I’ve been told my chimney is too short. Why does height matter?

The National Fire Protection Association (NFPA) and the International Residential Code (IRC) set the building code standards for chimney construction, including height.  For all residential chimneys, they must be 36” above the point where they pass through the roof AND 24” above any structure within 10 feet of the chimney.  The drawing below helps to understand this better.

The height of the chimney affects the draft (the way the chimney pulls air up and out from the home).  A chimney that is too short can affect the draft and can cause smoke from fireplaces to enter the room.  It can also make it more difficult to light a wood stove.  In addition, the minimum height requirements of the chimney help protect the roof from catching fire from sparks and/or burning embers that may make their way up into the chimney.