N.Y.C. Admin. Code § 27-869.02: § 27-869.02 Changes in appliance fuels.

(a) Conversion from gas to fuel oil or wood for heating appliances shall be made only if:

(1) the chimney design meets the requirements of this subchapter for the conversion fuel; and

(2) the chimney size is adequate to vent the combustion products from the new fuel.

(b) Conversion from solid or liquid fuels to natural gas fuels for heating appliances shall be made only if:

(1) the chimney design meets the requirements of this subchapter for the conversion fuel;

(2) the chimney is thoroughly cleaned prior to the conversion to remove collected flue deposits, which can spall off when gas is used as a fuel;

(3) the chimney size is recalculated for the new fuel;

(4) drains are installed to remove condensed water; and

(5) gas vents are installed within the chimney for venting purposes if required by the appliance listing.