The provisions of this chapter shall not apply to: (1) Boilers under federal control; (2) portable boilers used in pumping, heating, steaming and drilling in the open field; (3) portable boilers used solely for agricultural purposes; (4) steam heating boilers, hot water heaters and hot water heating boilers, when used in private homes or apartment houses of not more than five families; (5) hot water heaters approved by a nationally recognized testing agency that are equipped with adequate safety devices, including a temperature and pressure relief valve, (A) (i) having a nominal water capacity of not more than one hundred twenty gallons and a heat input of not more than two hundred thousand British thermal units per hour, (ii) used solely for hot water supply carrying a pressure of not more than one hundred sixty pounds per square inch and operating at temperatures of not more than two hundred ten degrees Fahrenheit, and (iii) not installed in schools, day care centers, public or private hospitals, nursing or boarding homes, churches or public buildings, as defined in § 1-1, or (B) (i) having a nominal water capacity of not more than ten gallons and a heat input of not more than twenty thousand British thermal units per hour, and (ii) installed in any occupancy; (6) antique or model boilers used in public, nonprofit engineering or scientific museums and operated for educational, historical or exhibition purposes having a shell diameter of less than twelve inches and a grate surface area of less than one square foot; and (7) public service companies, as defined in § 16-1.