Direct water heaters; water heating systems comprised of direct contact water heaters and optional equipment such as circulating pumps, heat exchangers, gas fired or oil burners, induced draft fans, stacks, economizers, electronic programmable control panels; air heating systems comprised of direct contact heaters and optional equipment such as circulating pumps, heat exchangers, gas fired or oil burners, induced draft fans, stacks, economizers, electronic programmable control panels; air and...