HVAC H1 Class I Lisense is basically for all boilers and hot water heaters.  The following is the definition supplied by the State of North Carolina:

87-21. (a) Definitions. – For the purpose of this Article: (2). The phrase "heating, group number one" shall be deemed and held to be the heating system of a building, which requires the use of high or low pressure steam, vapor or hot water, including all piping, ducts, and mechanical equipment appurtenant thereto, within, adjacent to or connected with a building, for comfort heating.

Class I allows you to work on all structures.