In a nutshell
A tank holds a fixed volume at temperature and needs time to reheat once drained. An on-demand unit warms water in passing: no running dry, but a ceiling on how many taps it can serve together. For a small to mid-sized household with modest simultaneous use, either works. For larger families with several showers at once, sizing becomes critical.
Working through it
1. Consider Toronto winters
Lake Ontario water entering a house in February is much colder than in August. A tankless heater must raise that cold water to shower temperature in a single pass. The colder the inlet, the lower the flow it can deliver at full temperature. Size for winter, not summer.
2. Check gas supply and venting
Gas tankless units need a large gas input. Older houses may have a small gas meter or narrow lines, which may need upgrading in consultation with Enbridge. Venting usually goes out a side wall, with clearances from windows, doors and property lines. Tank-type heaters often vent through the old chimney or a power vent.
3. Compare features
| Storage tank | Tankless | |
|---|---|---|
| Hot water supply | Limited by tank size | Endless, but capped by flow |
| Space | Takes floor space | Wall-mounted, compact |
| Standby losses | Some heat lost from the tank | Minimal |
| Maintenance | Periodic flushing | Regular descaling in hard water |
| Rental availability | Common | Available, less common |
4. Account for hard water
Toronto's moderately hard water leaves scale inside heat exchangers. Tankless units need periodic descaling, and some owners add a softener or scale filter. See our water heater flush page for upkeep basics.
Clues worth noticing
Signs it is time to rethink your water heater:
- Showers running cold partway through.
- A tank over ten years old with rust at the base.
- Rental charges that feel out of line with the age of the equipment.
- Plans to finish the basement and reclaim space.
Electric options
Some homes have no gas, especially condos. Electric tanks are simple and reliable. Whole-house electric tankless units need very large electrical capacity, often more than an older panel can supply. Heat pump water heaters are another option, using less electricity but needing space and a basement that does not get too cold.
Signals that it needs a licensed plumber
Call for an assessment of your gas supply, venting route and household demand before choosing. We can explain the options on our tankless water heater page and the replacement process on gas water heater replacement. If the current tank is rented, read rental water heater first.
Odd smells from drains while the heater is being changed are unrelated but worth noting; our sewer smell essay explains the common causes.
Calls we field, answered plainly
Will a tankless heater save money?
It reduces standby losses, but upfront cost, gas upgrades and maintenance affect the overall picture. Results vary by household.
Can a tankless heater run several showers at once?
A properly sized unit can, but undersized models struggle in winter. Sizing for your peak use is key.