The Rinnai default output temperature is 120°F. Residential cap is 140°F. Commercial units can go to 185°F with installer-set override. This page covers when to deviate from 120°F and how.
Why 120°F is the default
- Scald safety: 120°F water causes a third-degree burn in 5-10 minutes. 140°F does it in 5 seconds. The Consumer Product Safety Commission recommends 120°F for households with children or seniors
- Energy: every 10°F you raise the setpoint adds 3-5% to gas consumption
- Heat exchanger longevity: higher setpoints accelerate scale formation. 120°F vs 140°F roughly doubles the descaling interval
When to raise above 120°F
- Dishwasher and washing machine demand: some appliances expect 130-135°F at the supply. Solution: raise unit to 135°F and install a thermostatic mixing valve (TMV) at the hot-water output to deliver 120°F to fixtures. Most installs do this.
- Legionella prevention in larger homes or homes with infrequently used fixtures. Periodic 140°F flush kills bacteria.
- Hot-water loop temp loss — if your recirculation loop is long, the loop drops 5-10°F by the time water reaches the farthest fixture. Compensate by raising the source.
How to change the setpoint
- On the controller: press the temperature up/down buttons. Range 98°F to 140°F residential.
- In ControlR app: Home → Temperature → slider
- For commercial override (above 140°F): requires an installer to enable via the technician menu. This is intentional — Rinnai limits residential units to 140°F as a liability boundary
Temperature recommendations
| Household | Recommended setpoint |
|---|---|
| Children under 6 or seniors over 65 | 120°F, install anti-scald TMV at every fixture |
| Standard household | 120°F |
| Dishwasher/laundry needs 130°F+ | 135°F unit + 120°F TMV at fixtures |
| Concerned about Legionella | Weekly 140°F flush program (commercial setup) |
| Commercial / restaurant | 140°F minimum; 180°F for some sanitizers |
Common temperature problems
- Water not getting hot enough at setpoint: scale on the heat exchanger reducing output. See our flushing guide
- Lukewarm at start of draw: cold-sandwich effect, not a setpoint problem. See recirculation
- Temperature swings during draw: low gas pressure or modulation issue. See troubleshooting
Bottom line
Stay at 120°F unless an appliance forces you up — then use a thermostatic mixing valve to deliver 120°F at the fixture. Don't max the unit out to 140°F as a general policy; you'll pay for it in gas and descaling.