How They Work
How Tankless Water Heaters Work
No tank, no stored hot water — heat happens when you open the tap.
A traditional heater keeps tens of gallons hot around the clock, reheating as stored water cools. A tankless unit reverses that: opening a hot tap sends cold water through the unit, burners or elements heat it in passing, and hot water exits the other side. Close the tap, and heating stops.
That on-demand design is why tankless units hang on a wall — there's no tank to house, and no stored supply to deplete mid-shower.
Here's the part marketing skips: a tankless unit can only heat so much water at once. Every unit carries a rated flow — how many gallons per minute it can lift by the needed temperature rise. Stay inside that rating and hot water keeps coming. Exceed it — two showers plus the dishwasher on an undersized unit — and temperature drops. That's physics, not a defect — and why sizing matters more for tankless than for any other water heater decision.