http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
American national standard for gas water heaters
v. 1. Automatic storage type water heaters with inputs of 75,000 BTU per hour or less.--v. 3. Circulating tank, instantaneous and large storage type water heaters.
approved January 7, 1974 ; Secretariat, American Gas Association.