Ontario Building Code 188.8.131.52. Vertical Clearances above Ranges
(1) Except as provided in Sentence (2), framing, finishes and cabinetry installed directly above the location of the range shall be not less than 750mm above the level of range burners or elements.
(2) The vertical clearance described in sentence (1) for framing, finishes and cabinets located directly above the location of the range is permitted to be reduced to 600mm above the level of the elements or burners provided the framing, finishes and cabinets,
(a) are noncombustible, or
(b) are protected by,
(i) asbestos millboard not less than 6mm thick, covered with sheet metal not less than 0.33mm thick, or
(ii) a metal hood with a 125mm projection beyond the framing, finishes and cabinets.
So 600mm or 23 5/8".