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AO Smith Temperature Setting

AO Smith Water Heater Temperature Setting — What to Use & Why

The right temperature setting for an AO Smith water heater. 120°F default, dishwasher requirements, Legionella considerations, scald safety.

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Updated May 2026 · AO Smith Water Heaters

AO Smith ships every residential water heater factory-set at 120°F — the CPSC scald-safety standard. Most households should keep this default.

The 120°F default — why AO Smith ships there

  • Scald safety: 140°F causes third-degree burns in ~5 seconds; 120°F in ~5 minutes
  • Energy cost: every 10°F costs 3–5% more annually
  • Tank longevity: higher temps accelerate anode and tank corrosion

When to consider 130°F

  • Older dishwashers requiring 130°F+ input water (modern dishwashers have internal boost — verify your manual)
  • Legionella concern — multiplies at 77°F–113°F; 130°F+ kills it. Relevant for: vacation properties, immunocompromised members, large tanks with stagnant water
  • Long pipe runs — 130°F at tank → 115–120°F at distant fixture

How to change temperature

AO Smith gas tank (Signature Premier / ProMax / ProLine)

  1. Locate gas control valve at front-bottom of unit
  2. Rotate dial — typically marked A/B/C or 1–9, not °F
  3. Reference dial-to-temp table in user manual (see our AO Smith manuals hub)
  4. Wait 60 minutes; test at nearest faucet with thermometer

AO Smith electric tank (Signature 100 / ProMax electric)

  1. Shut off power at breaker
  2. Remove upper and lower thermostat access panels
  3. Pull aside insulation
  4. Set BOTH thermostats to same temperature with flathead screwdriver. AO Smith electric dials are direct °F markings.
  5. Replace insulation/panels, restore power, wait 60–90 min

AO Smith ProLine Tankless

Digital temperature control on front of unit or via wall remote. Press +/- buttons to set target. Range: 100°F – 140°F residential, up to 160°F on commercial-certified models. Effect is immediate.

AO Smith Voltex Hybrid

Front-panel digital display or iCOMM app. Press temperature button, use +/- to set, or set via app for remote control.

Best of both worlds — high tank + mixing valve

Pros set the tank to 140°F (kills Legionella, supports dishwashers) and install a thermostatic mixing valve at the tank outlet that blends to deliver 120°F at fixtures. Mixing valves cost $150–$300; require a plumber.

Bottom line

120°F is the right default for most AO Smith owners. Raise to 130°F only for dishwasher / Legionella / long-pipe-run reasons. For full maintenance procedure see our maintenance hub.