Inlet water temperature (°F) by US region
Typical published planning values — NOT a certified spec or professional advice. Efficiency, sizing and life vary by unit and installation; confirm on the EnergyGuide label and the manufacturer’s instructions. Water-heater installation, gas, venting, combustion, the temperature-&-pressure relief valve, and the scald / Legionella tradeoff of a temperature setting are a licensed plumber / gas fitter, manufacturer-instruction and local-code matter — not engineered here.
A tankless is sized by flow at your temperature rise (ΔT = desired output − inlet), and the inlet water temperature falls with latitude and the season. These are LABELED planning ranges — measure your own inlet if you can. A colder inlet means a bigger rise and less usable GPM. Use them with the tankless sizing calculator and the operating-cost calculator.
| US region | Inlet water temperature (°F) |
|---|---|
| Cold / northern | ~40–50 |
| Temperate / middle | ~50–60 |
| Warm / southern | ~60–77 |
LABELED planning ranges — measure your own inlet if you can. The colder the inlet, the bigger the temperature rise (ΔT) and the less usable GPM a tankless delivers. Snapshot: 2026-07-13.