Cover title. "ANSI Z83.6-1974" Approved May 24, 1974. "A consolidation, revision, and redesignation of American national standard for unvented gas-fired infrared radiant heaters, Z21.43-1968, and Addenda, Z21.43a-1971 and Z21.43b-1972, and American national standard for vented gas-fired infrared radiant heaters, Z21.51-1971, and Addenda, Z21.51a-1971 and Z21.51b-1973."