An altered duct system installed in an existing home shall be considered an Entirely New or Replacement Duct System when:

1. At least 75 percent of the ducting material by linear length is new, and

2. Any remaining components from a previous duct system are accessible> and can be sealed (e.g. register boots, plenums, etc.). See definition of accessible below.

Duct systems that do not meet the definition of an Entirely New or Replacement Duct Systems shall be considered an >existing> or >altered> duct system.