An on-demand unit that heats water as it flows instead of storing it — endless supply, 15–20-year lifespan, wall-mounted footprint. The trade-offs are install cost and flow-rate limits during simultaneous use, plus gas-line and venting requirements in retrofits.
Water-heater terms connect to tank vs tankless decisions, recovery rate for busy households, anode-rod maintenance against our region's water chemistry, and code requirements like expansion tanks.