(1) The rules in this subchapter do not apply to:

(a) boilers under federal control;

(b) steam heating boilers operated at not over 15 psig in private residences or apartments of six or less families or whenever a single boiler provides heat for six or less apartment (dwelling) units;

(c) hot water heating or supply boilers operated at not over 50 psig and temperatures not over 250 degrees F. when in private residences or apartments of six or less families or whenever a single boiler provides heat for six or less apartment (dwelling) units;

(d) unfired pressure vessels; or

(e) water heaters or water heating systems operating at pressures not exceeding 150 psig and/or temperatures not exceeding 210 degrees F. which are utilized to supply potable hot water as regulated by the state plumbing code. Maximum operating pressures and temperatures shall be determined by the listing(s) on the manufacturer's data plate. Examples of exempted water heaters and water heating systems include, but are not limited to, lined potable water heaters, hot water heaters of corrosion resistant elements utilized in conjunction with lined potable storage vessels, instantaneous type water heaters designed to deliver potable hot water without storage, water heating systems which utilize an approved heat exchanger to heat potable water and other similar systems.