You size a tankless water heater by the maximum flow rate (in gallons per minute) and the required temperature rise. Most Spokane-area homes need 7–11 GPM at a 70°F rise. A small condo may only need 5 GPM; a large home with multiple showers and a soaker tub may need 11+ GPM, sometimes requiring two units.
Typical sizing
- Small home / 1–2 baths — 5–7 GPM
- Average 3-bath home — 7–9 GPM
- Large home or family — 9–11 GPM
- Multi-bath / soaker tub — 11+ GPM or twin units
- Add 1–2 GPM buffer for future remodels
We size with a full peak-demand calculation. See our tankless water heater service.
