A tankless water heater — sometimes called an instantaneous or demand-type heater — does exactly what the name suggests. It heats water only as it flows through the unit. There is no storage tank maintaining a reservoir of hot water. When you open a hot-water tap, cold water enters the unit, passes over a heat exchanger powered by natural gas, propane, or electricity, and exits at your set temperature. When you close the tap, the unit shuts off.
This is fundamentally different from a conventional storage-tank heater, which keeps 40 to 60 gallons of water hot at all times — including overnight, while you're at work, and during the weeks you're on vacation. That constant reheating is called standby loss, and it's the core inefficiency that tankless systems eliminate. The U.S. Department of Energy identifies standby heat loss as the primary reason storage tanks use more energy than demand-type heaters.
Here's where expectations often go sideways. "On demand" does not mean "instant." When you turn on a distant tap, the hot water still has to travel through your home's piping to reach you — exactly the same delay you'd experience with a tank. In fact, Natural Resources Canada notes that wait times for hot water can actually increase when switching to a tankless system, because the unit needs a moment to detect flow, ignite, and bring water up to temperature before it even starts its journey through the pipes.
If instant hot water at every tap is important to you, a recirculation pump — either built into the unit or added as an accessory — can solve the problem. But that's an additional cost and an additional component to maintain. It's worth knowing before you buy, not after.
Gas tankless heaters (natural gas or propane) dominate the Canadian whole-home market. They deliver higher flow rates, heat water faster, and can handle multiple fixtures running simultaneously. They require venting to the exterior and a gas supply line sized to their BTU input — both of which add installation complexity.
Electric tankless heaters are simpler to install and don't need venting. But whole-home electric models demand enormous amperage — often 100 to 150 amps on dedicated circuits — which can require a full electrical panel upgrade. Most Canadian homes on 100-amp or even 200-amp service may not have the spare capacity. Small electric point-of-use units (for a single sink or shower) are a different story: they're inexpensive, easy to install, and work well as supplements to an existing system.
A whole-home electric tankless water heater can require three or four dedicated 40-amp breakers. If your home's electrical panel doesn't have that capacity, you're looking at a panel upgrade costing $2,000–$4,000 before the water heater itself is even installed. For most Canadian homes, gas tankless remains the more practical whole-home option.
