Two standards, by the clock
Section 1 defines the term in two halves: "between 11:00 pm of any day and 6:00 am of the next following day an air temperature in the centre of each reasonably ventilated room of not less than 16.67 degrees Celsius (62 degrees Fahrenheit) and between 6:00 am and 11:00 pm of any day an air temperature in the centre of each reasonably ventilated room of not less than 20 degrees Celsius (68 degrees Fahrenheit)".
That overnight setback is permission, not an obligation to lower the heat. A building that holds 20 degrees around the clock is compliant; one that drops to 18 at 2 a.m. is also compliant, and one that drops to 15 is not.
The measuring point is the centre of the room, and the room must be reasonably ventilated. That differs from the municipalities that specify a height above the floor, and it means a compliance reading taken to Toronto's or Oakville's method is not the reading Ottawa's bylaw describes.
No season at all
Section 3: "No landlord of a building or part of a building which is rented or leased as dwelling or living accommodation and which, as between the tenant or lessee and the landlord, is normally heated by or at the expense of the landlord, shall fail to maintain at all times adequate and suitable heat therein."
"At all times" is the operative phrase and the bylaw sets no dates anywhere. A cold night in August is governed by the same rule as a cold night in January.
The qualifier is the same one that appears across the province: it bites where the accommodation is normally heated by or at the expense of the landlord. Where the tenant holds the heating account, the municipal duty does not attach — though the landlord's obligations under sections 20 and 21 of the Residential Tenancies Act still do.
The notice mechanism
Section 4 is unusual in being mandatory on the enforcement side: where a landlord fails to maintain adequate and suitable heat, "the Chief shall issue" a written Notice requiring the landlord to maintain it and "specifying the time allowed for compliance". That wording was amended by By-law 2026-225.
So the first formal step in Ottawa is a dated notice with a deadline attached, which then becomes the document a later prosecution is built on. Sections 6 to 8 deal with failure to comply and sections 9 and 10 with offences and penalties.
For a landlord the practical consequence is that the clock is written down by the City rather than argued about afterwards. What you can show you did between the notice and its deadline is the whole of your position.