Gas-fired swimming pool heaters and swimming pool boilers shall comply with all applicable American Standards Association requirements for this class of service, including the American Gas Association (A.G.A.) and the American Society of Mechanical Engineers (A.S.M.E.) standards. Oil burning equipment must be listed by Underwriters' Laboratories or other nationally recognized testing agency. All equipment shall be of the direct or indirect type and shall carry the corresponding seal of approval by the appropriate agencies.
('69 Code, § 6-113)