Tankless Water Heater
A water heater that heats water on demand as it flows through, rather than storing a tank of hot water, giving endless hot water and a smaller footprint.
A tankless water heater, also called an on-demand unit, has no storage tank. When you open a hot tap, a flow sensor fires a powerful gas burner or a bank of electric elements that heat the water as it passes through, in real time. Because there is no tank, there is no standby heat loss from keeping 50 gallons warm around the clock, and there is no finite reservoir to run dry, the unit delivers hot water as long as the tap is open.
The trade-offs are capacity and install complexity. A tankless unit is rated in gallons per minute at a given temperature rise, so a single unit may comfortably run two showers in a warm climate but struggle with simultaneous demand where incoming water is cold. Gas models often need a larger gas line and dedicated stainless venting, which is why installed cost runs well above a tank swap. Annual descaling is also part of ownership, especially in hard water, since scale chokes the narrow heat exchanger.
The payoff is longevity and efficiency. A well-maintained tankless unit lasts around 20 years, roughly double a tank, and uses less energy by heating only what you draw. For households that regularly drain a tank or want to reclaim closet space, the math improves with every year of service. For a same-day emergency swap, though, a like-for-like tank usually wins on speed and first cost.
Talking to a contractor about this?
Run the project past a licensed plumbing pro first. Calls are answered around the clock and routed to a pro serving your area.
- Anode Rod : A sacrificial metal rod inside a tank water heater that corrodes in place of the steel tank, protecting it from rust for as long as the rod lasts.
- T&P Relief Valve (TPR) : A safety valve on every tank water heater that releases water if temperature or pressure climbs too high, preventing the tank from rupturing or exploding.
- Thermal Expansion Tank : A small tank that absorbs the pressure increase created when water heats and expands in a closed plumbing system, protecting the water heater and valves.