Tank or tankless in an Ontario winter
Tankless is not simply the newer, better version of a tank. They fail in different ways and they are sized by different numbers, and in an Ontario winter one of those numbers moves a long way.
The difference that actually matters
A tank stores hot water and reheats it, so it is limited by how much it holds and how fast it recovers. Tankless heats water as it passes through, so it is limited by flow: how many litres a minute it can raise to temperature at once. A tank runs out. A tankless does not run out, it runs cool if you ask for more than it can heat at that moment.
Why an Ontario winter changes the sizing
A tankless unit is rated by how far it can raise the incoming water temperature at a given flow. Municipal water arriving in February is a great deal colder than in August, so the same unit that comfortably runs two showers in summer may manage one and a half in winter. Size for the cold-weather rise, not the headline number on the box.
What suits a tank
Predictable demand, a household whose hot water use clusters at the same times, an existing vent and gas line that already fit, and a preference for a lower installed cost. Tanks are simple, and simple things have fewer ways to be wrong.
What suits tankless
Long or overlapping demand, limited floor space, a household that runs out of hot water rather than merely waiting for it, and a willingness to spend more on the install. Venting and gas supply often need work, which is a real cost and should be quoted before you book rather than found on the day.
The honest tie-breaker
If your current tank meets your needs and you are replacing it because it is old, another tank is usually the sensible choice. If you regularly run out of hot water, tankless solves the actual problem and a bigger tank only postpones it. Anyone who recommends tankless without asking how your household uses hot water is selling a category, not solving a problem.