The equipment sentence that does the work
Section 1.3 defines adequate and suitable heat as "a minimum air temperature, in the part of the accommodation which is normally heated, of at least twenty degrees Celsius (20°C)", and then adds: "Portable heaters may not be utilized to achieve adequate and suitable heat."
That second sentence closes the argument a landlord with a failing furnace usually reaches for. Space heaters in the living room do not make the unit compliant, even if the thermometer reads 20.
Section 2.6 sets the season: the landlord of every rental unit "which, as between tenant or lessee and the landlord is normally heated by or at the expense of the landlord, shall maintain… adequate and suitable heat between the 15th day of September in each year and the 31st day of May in the following year".
Cooling, but only if it is already there
Section 2.7 obliges the landlord of every rental unit "equipped with a Central Air Conditioning System" to maintain adequate and suitable cooling, defined in section 1.2 as no more than 26 degrees in the part of the accommodation normally used.
The same anti-substitution rule appears: "Portable air conditioning units and air conditioning window shakers may not be utilized to establish suitably cooled air." A landlord cannot discharge a central-AC obligation by handing over a window unit.
As everywhere else in Ontario, none of this requires installing air conditioning where there is none.
Additional dwelling units are named
The bylaw defines "Additional Dwelling Units" or "ADUs" as a self-contained dwelling unit either inside a permitted residential dwelling or in an accessory structure secondary to the main building on the same lot.
Basement suites and garden suites are therefore addressed on their face rather than left to argument about whether a vital services bylaw reaches them — worth knowing if your rental is a converted basement.
Whitby and Ajax run closely parallel bylaws, as neighbouring Durham municipalities often do. If you hold units in both, the heat figure and the season are the same; the drafting around cooling and hot water is not, so read each rather than assuming.