# Water heater temperature setting, 120 or 140 F: what each number does, what the dial marks mean, and who should not turn it down > CPSC urges 120 F and prints 140 F as a 6-second burn; DOE puts the saving at 4% to 22% a year. Dishwashers without a booster are the exception, with a mixing valve. | | | |---|---| | Source | https://ownerspec.com/plumbing/guides/water-heater-temperature-setting-120-or-140/ | | Publisher | OwnerSpec (https://ownerspec.com/) | | Published | 2026-10-10 | | Updated | 2026-10-10 | | Facts verified | 2026-10-10 | | Disclosure | Contains affiliate links. OwnerSpec may earn a commission at no cost to the reader. | --- ## Short answer Set a residential tank water heater to 120 F unless an appliance in the house needs hotter water. The U.S. Consumer Product Safety Commission's Publication 5098 urges all users to lower their water heaters to 120 F and prints 140 F as a third-degree burn in six seconds for most adults. DOE's Energy Saver page (archived 2 July 2026) says most households only require 120 F and puts the annual saving from turning down a 140 F tank at 4% to 22%. The makers agree: A. O. Smith's electric manual factory-sets its thermostats at 120 F, Bradford White's electric HOT mark is about 120 F, and Rheem's gas control ships at its lowest mark with 120 F as the recommended starting point. The exception DOE names is a dishwasher without a booster heater, which may need 130 F to 140 F; the makers pair that with a mixing valve, not a hotter tap. Dials are approximate, so confirm with a thermometer at the farthest tap. ## Fact sheet - **Answer:** Set a residential tank water heater to 120 F unless an appliance needs hotter water. CPSC urges 120 F and prints 140 F as a third-degree burn in 6 seconds; DOE's archived Energy Saver page puts the saving from 140 F to 120 F at 4% to 22% a year. AO Smith's electric manual factory-sets 120 F, Bradford White's HOT mark is about 120 F, and Rheem names 120 F as the starting point. - **Basis:** CPSC Publication 5098 (120 F recommendation and burn times), the DOE Energy Saver savings project page (archived 2 July 2026), and the installation manuals from A. O. Smith, Bradford White and Rheem for factory settings, dial marks and scald tables. - **Assumptions:** A US residential storage (tank) water heater, gas or electric. Tankless units, which hold a set outlet temperature, are not covered here.; The dial marks and degree values are Rheem's, from its gas FVIR manual, and Rheem labels them approximate. Other makers' dials differ and may print no temperatures.; Dishwasher temperature needs are quoted from DOE and the water heater makers only; no dishwasher maker's manual could be opened this session.; Model plumbing code text is the 2024 IRC as adopted in Texas; codes are adopted locally and vary. - **Method:** Spec comparison of published documents, read on 10 October 2026: the CPSC PDF, the archived DOE page, the CDC potable-water toolkit, three maker manuals and the up.codes text of the IRC. Burn times are printed per source and never blended, because CPSC prints 6 seconds at 140 F while the makers print under 5. No measurements were taken. - **Primary source:** [CPSC Publication 5098, Avoiding Tap Water Scalds (PDF)](https://www.cpsc.gov/s3fs-public/5098-Tap-Water-Scalds.pdf) (government or regulatory source) - **Facts verified:** 2026-10-10 - **Last updated:** 2026-10-10 - **Canonical URL (cite this):** https://ownerspec.com/plumbing/guides/water-heater-temperature-setting-120-or-140/ If the complaint is that there is no hot water at all, the dial is not your problem: start with the [no hot water guide](/plumbing/guides/water-heater-no-hot-water-electric-gas/) and, on an electric tank, the [heating element parts page](/plumbing/parts/water-heater-heating-element-by-wattage-and-voltage/). ## What does each setting do? The three documents that matter print different numbers for the same dial, so the table keeps them apart. | Setting | CPSC 5098 says | DOE Energy Saver (archived) says | Maker manuals say | |---|---|---|---| | 120 F | The temperature CPSC urges all users to set; a five-minute exposure could still result in third-degree burns | Enough for most households; 4% to 22% annual saving against 140 F; slows mineral buildup and corrosion | A. O. Smith electric manual factory setting; Bradford White HOT mark (about 120 F); Rheem recommended starting point; burn in more than 5 minutes | | 130 F | Third-degree burns in thirty seconds for most adults | Lower end of the range a dishwasher without a booster may require | Rheem mark A; about 30 seconds to burn | | 140 F | Third-degree burns in six seconds | Setting some manufacturers use; scalding hazard; the setting DOE says a person with a suppressed immune system may consider | Rheem mark B; burn in less than 5 seconds; Canadian factory preset per Bradford White | | 150 F | Third-degree burns in two seconds | Not addressed | Rheem mark C; about 1-1/2 seconds to burn | Burn times differ by source because each publishes its own table: CPSC prints six seconds at 140 F, while Rheem credits its under-5-second figure to the Shriners Burn Institute and A. O. Smith's Figure 8 prints the same. None of them is blended here. The saving is real but not large. DOE's archived page prints 4% to 22% a year, and the [shower cost calculator](/plumbing/calculators/shower-water-and-energy-cost-calculator/) shows how much of that is the shower. A tank that is also too small for the house is a different problem, sized on the [first hour rating calculator](/plumbing/calculators/water-heater-size-first-hour-rating/). ## What do the dial marks mean? Gas water heaters put the thermostat in the gas control valve near the bottom of the tank, and most of them print words or letters, not degrees. A. O. Smith's info page says its gas dials may show temperatures or words such as Low, Medium and Hot. Only Rheem's manual prints a conversion, and it calls every value approximate. | Rheem gas control mark | Approximate temperature (Rheem AP23060) | |---|---| | Low | 91 F (33 C) | | Hot | 125 F (52 C) | | A | 130 F (54 C) | | B | 140 F (60 C) | | C | 150 F (66 C) | | Very Hot | 155 F (68 C) | Rheem's manual also says water above 125 F can cause severe burns, so on that dial the recommended 120 F sits below the Hot mark. Bradford White's gas manual, in the text version read for this page, does not print its dial marks at all. Rheem's hybrid heat pump tank is the one unit here with a digital control: it ships at 120 F in its default ENERGY SAVER mode, and anything above 140 F needs a high-temperature mode enabled in the controller. ## How do you adjust an electric tank? An electric tank has two heating elements, upper and lower, and each has its own thermostat behind a screw-on panel. CPSC's instructions are: shut off the current at the breaker or remove the fuse, remove the upper and lower access panels, and set both thermostats to a common temperature. A. O. Smith's manual 185762 adds the detail. Do not adjust a thermostat with power on. Fold the insulation up, leave the plastic personnel protectors in place, turn the adjustment knob with a flat-tip screwdriver, then replace the insulation and panels before restoring power. The same manual says it is not necessary to adjust the upper thermostat, but if it is raised above 120 F it should not be set higher than the lower one. CPSC and A. O. Smith differ on that point, so follow the manual printed for your tank. Bradford White's electric manual says its dial turns clockwise to increase temperature. If you have the panels off and the tank is slow to recover, the [element resistance test](/plumbing/calculators/water-heater-element-resistance-ohms-test/) tells you whether an element has failed before you blame the thermostat. ## Who should not simply turn it down? Two cases, and both end in a mixing valve rather than a hotter tap. | Reason to run hotter | Who prints it | What they pair it with | |---|---|---| | Dishwasher without a booster heater may require 130 F to 140 F | DOE Energy Saver (archived) | Mixing valves or other temperature-regulating devices on taps used for washing or bathing | | Dishwashers and clothes washers may require hotter water | Bradford White electric and gas manuals; A. O. Smith; Rheem | Bradford White: an ASSE approved mixing valve if the thermostat is raised | | Suppressed immune system or chronic respiratory disease | DOE's words: "you may consider keeping your hot water tank at 140 F" | Mixing valves at taps used for washing or bathing | DOE's page also says that at 120 F there is a very slight risk of promoting legionellae and that this level is still considered safe for the majority of the population. The CDC toolkit that prints 140 F storage and 120 F minimum circulation is written for building water systems, with thermostatic mixing valves as close as possible to fixtures; it is quoted here, not applied to a house. This page makes no claim of its own about any of that. A mixing valve is a valve that blends hot and cold to a set outlet temperature. Two standards show up, and they are not the same job. Rheem's manual recommends a valve complying with ASSE 1017, Temperature Actuated Mixing Valves for Hot Water Distribution Systems, which sits at the heater. The 2024 IRC as adopted in Texas, Section P2713.3, requires bathtub and whirlpool valves to have a temperature-limiting device to ASSE 1070 with a 120 F maximum setting, and Section P2708.4 caps individual shower valves at a 120 F maximum setting. Codes are adopted locally, so your inspector's copy governs. **Before you turn the dial up** Open the dishwasher manual first. If it lists a booster heater, the tank stays at 120 F and nothing else changes. If it does not, raise the tank and fit the ASSE mixing valve the heater maker names, because every bath and shower in the house will otherwise see 140 F water: 6 seconds to a third-degree burn by CPSC's table, under 5 by the makers'. ## What else changes when you raise it? Hotter water expands more and the tank runs more cycles. Two existing pages cover what follows: a [T&P relief valve that starts dripping](/plumbing/guides/water-heater-tp-relief-valve-dripping/) after a setting change, and the [thermal expansion tank](/plumbing/guides/thermal-expansion-tank-when-required/) that a closed supply needs regardless of setting. DOE's archived page says 120 F also slows mineral buildup, which is the sediment behind a [popping water heater](/plumbing/guides/water-heater-popping-noise-sediment-flush/). ## What should you do first? 1. Read the setting at a tap, not the dial: DOE says dials are often inaccurate, so hold a thermometer under the farthest tap. 2. Check the dishwasher manual for a booster heater before deciding the tank needs more than 120 F. 3. Gas tank: turn the control toward the recommended 120 F starting point, which on a Rheem dial is below Hot. 4. Electric tank: breaker off, both panels off, set the thermostats per the maker's manual, panels back on, power on. 5. Raising it anyway: fit the ASSE mixing valve the manual names and recheck every bathroom tap with the thermometer. ## Frequently asked questions ### Is 120 F hot enough for showers and dishes? DOE's Energy Saver page says most households only require 120 F, and CPSC says to use the lowest setting that satisfies the clothes and dish washing machines. The one appliance that may need more is a dishwasher without a booster heater: DOE says it may require 130 F to 140 F for optimum cleaning. Check the dishwasher's own manual before raising the tank for it. ### What do the A, B and C marks on a gas water heater dial mean? On Rheem's residential gas control, the manual prints approximate values of Low 91 F, Hot 125 F, A 130 F, B 140 F, C 150 F and Very Hot 155 F. A. O. Smith's info page says its gas dials may show temperatures or words such as Low, Medium and Hot without printing a table. Marks are approximate, so measure the result at a tap with a thermometer. ### Why does my electric water heater have two thermostats? Most residential electric tanks have an upper and a lower heating element, each with its own thermostat behind a screw-on panel. CPSC says both must be set to a common temperature after the breaker is off. A. O. Smith's manual says the upper one need not be adjusted, but if raised above 120 F it should not exceed the lower thermostat. Follow your unit's manual. ### Should I set the tank to 140 F because of Legionella? DOE's archived page says there is a very slight risk of promoting legionellae at 120 F, that this level is still considered safe for the majority of the population, and that someone with a suppressed immune system or chronic respiratory disease may consider 140 F with mixing valves at bathing taps. CDC's 140 F storage figure is written for building water systems. Ask your health department, not this page. ### Is a mixing valve required if I set the heater above 120 F? Rheem's gas manual recommends a mixing valve complying with ASSE 1017 near the heater, and Bradford White advises an ASSE approved mixing valve whenever the thermostat is raised for a dishwasher or washer. Separately, the 2024 IRC as adopted in Texas limits shower valves and tub temperature-limiting devices to a 120 F maximum setting. Your local code decides what is required at the fixture. ## Sources - [CPSC Publication 5098, Avoiding Tap Water Scalds (PDF)](https://www.cpsc.gov/s3fs-public/5098-Tap-Water-Scalds.pdf) (government or regulatory source) - [DOE Energy Saver, Do-It-Yourself Savings Project: Lower Water Heating Temperature (archived 2 July 2026, Wayback Machine; the live energy.gov page returned 404 on 10 October 2026)](http://web.archive.org/web/20260702092155/https://www.energy.gov/energysaver/do-it-yourself-savings-project-lower-water-heating-temperature) (manufacturer or vendor document) - [CDC, Controlling Legionella in Potable Water Systems (building water system toolkit module)](https://www.cdc.gov/control-legionella/php/toolkit/potable-water-systems-module.html) (government or regulatory source) - [A. O. Smith, Instruction Manual, Residential Electric Water Heaters, document 185762 (PDF)](https://assets.hotwater.com/damroot/Original/10001/185762.pdf) (manufacturer or vendor document) - [A. O. Smith info center, Water heater temperature setting](https://www.hotwater.com/info-center/water-heater-temperature-setting.html) (manufacturer or vendor document) - [Bradford White, Installation and Operation Manual, Electric Water Heater, 238-44422-00 (PDF)](https://docs.bradfordwhite.com/I&O/238-44422-00_Current.pdf) (manufacturer or vendor document) - [Bradford White, Installation and Operation Manual, Gas-Fired FVIR Water Heater, 238-51012-00 (PDF)](https://docs.bradfordwhite.com/I&O/238-51012-00_Current.pdf) (manufacturer or vendor document) - [Rheem, Residential Gas FVIR Water Heater Use & Care Manual AP23060 Rev 01 (PDF)](https://files.myrheem.com/webpartners/ProductDocuments/BC7547B1-9AD5-4B7E-9C22-4B5FA3CC360F.pdf) (manufacturer or vendor document) - [Rheem, Electric Residential Hybrid Water Heater Use and Care Manual AP23657 Rev 04 (PDF)](https://media.rheem.com/blobazrheem/wp-content/uploads/sites/36/2025/01/AP23657-Use-Care-Manual.pdf) (manufacturer or vendor document) - [IRC 2024, Chapter 27 Plumbing Fixtures, Sections P2708.4 and P2713.3 (Texas adoption, up.codes viewer)](https://up.codes/viewer/texas/irc-2024/chapter/27/plumbing-fixtures) (manufacturer or vendor document) --- Citation: OwnerSpec, "Water heater temperature setting, 120 or 140 F: what each number does, what the dial marks mean, and who should not turn it down", https://ownerspec.com/plumbing/guides/water-heater-temperature-setting-120-or-140/, facts verified 10 October 2026. 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