Rheem ships every residential water heater factory-set at 120°F. This is the CPSC scald-safety standard and the right setting for most households. Some homes have reasons to deviate — dishwasher manufacturers spec 120°F input, Legionella prevention guidance pushes toward 130°F+, and energy-conscious owners sometimes target 110°F. This page covers the trade-offs and the actual procedure for changing temperature on each Rheem product family.
The 120°F default — why Rheem ships there
Three reasons:
- Scald safety: at 140°F, third-degree burns happen in ~5 seconds of skin contact. At 130°F, ~30 seconds. At 120°F, ~5 minutes. The CPSC and OSHA recommend 120°F as the upper bound for residential delivery.
- Energy: every 10°F increase raises annual operating cost by 3–5%. The difference between 120°F and 140°F is meaningful over a 12-year tank life.
- Tank longevity: higher tank temperatures accelerate anode consumption and tank-shell corrosion. Tanks running at 140°F+ regularly fail 2–3 years earlier than tanks at 120°F.
When to consider 130°F
- Dishwasher manufacturer requirement: some older dishwashers require 130°F+ input water for proper sanitization. Modern dishwashers (post-2015) include internal boost heaters and work fine with 120°F input. Check your dishwasher manual.
- Legionella concern: Legionella bacteria multiplies in stagnant warm water (77°F–113°F). Maintaining tank temperature at 130°F+ kills the bacteria. Relevant for: vacation properties with intermittent use, immunocompromised household members, large-tank installs where water sits unused for days.
- Long pipe runs to remote fixtures: hot water cools traveling through long pipes; 130°F at tank can deliver 115–120°F at the far fixture.
When to consider 110°F
- Households with small children: 110°F essentially eliminates scald risk
- Single-occupant adults with low demand: energy savings without compromise
- Drought-stricken regions where every drop matters: lower temperature means less need for cold-water mixing at fixtures
Trade-offs of 110°F: insufficient for dishwashers without internal boost; Legionella risk increases; long pipe runs may deliver only 95–100°F at the far fixture.
Best of both worlds — tank high, mixing valve at fixtures
The professional approach for households with conflicting priorities: set the tank to 140°F (kills Legionella, supports dishwashers, provides hot reserve), install a thermostatic mixing valve at the tank outlet that blends tank water with cold to deliver 120°F at all fixtures. Mixing valves cost $150–$300 and require a plumber to install but solve every trade-off simultaneously.
How to change temperature — Rheem gas tank
- Locate the gas control valve at the front-bottom of the unit
- Identify the temperature dial — typically marked with letters (A, B, C) or numbers (1–9), not °F
- Reference the dial-to-temperature table in the user manual (or our Rheem manuals hub)
- Rotate the dial to the desired setting
- Wait 60 minutes for the tank to stabilize at the new temperature, then test at the nearest hot-water faucet with a thermometer
Typical Rheem gas dial mappings:
- "WARM" or position A: ~95–105°F
- "HOT" or position B / mid-range: ~115–120°F
- "VERY HOT" or position C / upper range: ~130–140°F
- Highest setting (often marked "HOT" with arrow): ~150°F
How to change temperature — Rheem electric tank
- Shut off power at the breaker
- Remove the upper and lower thermostat access panels
- Pull aside the insulation
- Set both thermostats to the same temperature using a flathead screwdriver. The dial has direct °F markings on Rheem electric models.
- Replace insulation and panels
- Restore power
- Wait 60–90 minutes, test at a faucet
Important: set BOTH upper and lower thermostats to the same temperature. Mismatched settings cause the tank to cycle erratically.
How to change temperature — Rheem tankless (RTGH, RTEX)
Tankless models have digital temperature control on the front of the unit (or via remote control / EcoNet app):
- Press the +/- buttons on the unit's display or wall remote to set the target temperature
- EcoNet-connected models: open the EcoNet app, navigate to the unit, set temperature directly
- Temperature change takes effect immediately — no waiting period
Tankless Rheem typical range: 98°F – 140°F residential, up to 160°F on commercial-certified models.
How to change temperature — Rheem ProTerra heat pump
Front-panel digital display or EcoNet app:
- Press the temperature button on the front panel
- Use +/- to set target temperature
- EcoNet: set in the app for remote control
ProTerra has 4 operating modes — Hybrid, Heat Pump only, Electric only, Vacation. Temperature setting applies across all modes; recovery speed depends on the mode selected.
Testing actual delivered temperature
- Let the hot-water tap run for 2 minutes (clear the cold water from the pipe)
- Hold a digital thermometer in the stream for 30 seconds
- Verify the reading matches your tank setting within 5°F
If delivered temperature is significantly below tank setting: check for a malfunctioning mixing valve at the tank, leaking hot-water pipe, or undersized hot-water pipe causing heat loss.
Bottom line
120°F is the right default for most Rheem owners. Step up to 130°F only if you have specific dishwasher, Legionella, or pipe-run reasons. The professional solution for conflicting priorities is tank at 140°F + thermostatic mixing valve at outlet for 120°F delivery. For specific products see our Rheem water heater lineup. For maintenance procedures see our Rheem maintenance hub.