The range an air terminal may extend above a residential type chimney without additional support is from ...

The range for how far an air terminal may extend above a residential-type chimney without additional support is 10 inches to 24 inches. This specification is based on established lightning protection standards which ensure that air terminals can provide effective lightning protection while also maintaining structural integrity and avoiding interference with chimney function. Extending an air terminal beyond this range without additional support can put undue stress on the chimney structure, potentially cause damage, and impede the effective functioning of the chimney. Thus, the selection of this range reflects both safety and effectiveness principles in lightning protection.