water-heater-temperature-for-shower
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The person typing “water heater temperature for shower” wants to know whether the heater setting controls the water in the shower, and whether 120 degrees Fahrenheit is the right number. The sources answer yes in general and no in detail. The CPSC and the Illinois plumbing code both use 120 degrees as the reference point. A Baltimore study of 976 urban homes found that “Hot water temperature was unsafe in 41% of homes.” This article explains how the heater setting relates to the water that reaches a shower, what the policy studies reported, and where mixing valves fit. It gives no adjustment or installation steps.
Quick answer
- The heater setting is the main control on hot water temperature, but the water at the shower can differ from the dial. Tank temperature is not constant, and pipes change what arrives.
- The 120 degree figure is a voluntary standard that manufacturers adopted in 1988, based on a CPSC recommendation.
- In the Baltimore study, electric heaters were more likely than gas heaters to have safe temperatures, and homes with more gallons per person were more likely to be at or below 120 degrees.
- Mixing valves are the protection the sources describe for the fixture end. Policy results differ: Washington reported a drop in scalds, New York City did not, and Ontario reported fewer scalds but no change in hospitalizations.
Why the setting does not fix the shower temperature by itself
The NIH study explains that “As a hot water tank is depleted, replenished and reheated, water temperature will not be constant throughout the tank.” That means the water drawn at the moment you turn on the shower depends on how much hot water has been used and how recently the heater has run. A steady setting does not guarantee a steady temperature.
The heater is not the only factor. Both the Illinois standard and the Ontario regulation describe mixing valves as a way to limit the temperature that reaches the fixtures, and the valve section below covers them. The sources do not measure how the temperature at a given shower compares with the tank setting in a given house.
What the 120 degree recommendation is based on
The 120 degree figure has a clear origin in the sources. The NIH study says that the Consumer Product Safety Commission recommends that water heater manufacturers preset heaters to 120°F. The study describes earlier state action: “Efforts to regulate tap water temperature at the state level began in Florida in 1980 when the state legislature called for water heater temperatures to be pre-set at 125°F.” Manufacturers later adopted 120°F voluntarily, and the same study notes that “Few studies on the prevalence of hot water temperatures at or below this recommended level have been conducted since this standard was adopted.”
That gap matters for a shopper or homeowner. A preset tells you what the factory intended, not what the water is doing in a particular house in a particular year. The Baltimore study reports that 41% of its homes were unsafe, so a substantial share of homes still ran above the level the standard describes.
What the Baltimore study found about heaters and households
The study, published in the Journal of Burn Care and Research, recorded hot water temperature, the type and size of each water heater, the manufacture date, the thermostat setting, and household details in 976 urban homes. Its results are specific and worth reading in full. The authors report that “Hot water temperature was unsafe in 41% of homes.”
Several findings relate directly to the heater. The study says that “electric water heaters were more likely to have safe hot water temperatures than gas water heaters”. It also reports that “For 11% of gas water heaters, the water temperature was ≥ 130°F, although the gauge was set at less than 75% of its maximum setting.” In other words, a gas heater can run hot even when its dial is not near the top. And it reports that “Water heaters with more gallons per person in the household were more likely to be at or below the recommended 120°F.”
Homes also differed by tenure. The study reports that homeowners were more likely than renters to have safer temperatures, at 63% against 54%. That is a difference between groups in one city, not a measure of how any single landlord or owner manages a heater.
The authors conclude that “Our results suggest that hot water temperatures remain dangerously high for a substantial proportion of urban homes despite the adoption of voluntary standards to preset temperature settings by manufacturers.” The sample describes urban Baltimore homes. It does not estimate the rate for the whole United States.
What the state and city rules reported
Three policies are described in the sources. Each one reached a different result, and the table below keeps the reported outcome separate from the rule itself.
| Policy | Requirement as the source describes it | Reported result |
|---|---|---|
| Washington state, 1983 | Manufacturers to preset new water heaters, and landlords to set rental water heaters at 120°F | “resulted in significantly reduced household hot water temperatures and injuries resulting from scalds in King County, Washington” |
| New York City, 1996 amendment | Multi-unit dwellings constructed or renovated after 1997 to have water heaters set at 120°F | The evaluation did not find an effect on the incidence of tap water scald burns |
| Ontario, Building Code, September 2004 | New or renovated residential buildings to lower the maximum heater setting to 120°F | A significant decrease in monthly ambulatory scald cases; no significant change in hospitalization length of stay |
The Washington law is described in the NIH study as enacted in 1983 and applied to both manufacturers and landlords. The New York City result is the one the NIH study describes as no effect. The Ontario study reports the change in ambulatory cases and the lack of change in length of stay, and it concludes that hospitalized cases did not change significantly.
The gap between the New York result and the Washington result matters. The NIH study says the Washington law resulted in lower household temperatures, and the New York evaluation did not find an effect on injuries. The sources do not say why the two results differ, and this article does not guess.
Where mixing valves fit
The Illinois standard describes a valve arrangement for water heaters used for space heating as well as hot water supply. It says that “A thermostatic mixing valve, conforming to ASSE 1017, shall be installed on the hot water line to the plumbing fixtures.” The same paragraph requires “A single check valve shall be installed in the cold water line supplying the water heater.” The text explains the purpose of that check valve: “This will prevent hot water backing up from the heating unit to the plumbing fixtures.”
Ontario approaches the problem from the building side. The Ontario study says that “all new residential buildings must have antiscalding mixing valves installed at either the outlet of the water heater or at each hot water faucet in a home”. It also explains when older buildings must comply: “Existing buildings must follow this regulation once a water heater is replaced or the existing plumbing system is extended or altered.” The Ontario text ties that requirement to replacing the heater or altering the plumbing.
The Baltimore authors call for stronger prevention and name mixing valves as one option. The sources do not give a cost, a brand or a model for a valve, and this article does not recommend one.
Who should handle the setting
The CPSC text describes procedures for lowering water heater temperature, and the procedures differ by heater type. It also says that consumers should consider lowering the thermostat to the lowest setting that still meets hot water needs for clothes and dish washing. This article does not repeat those procedures. Work on an electric or gas water heater, a valve or a connection is for a licensed plumber or electrician. A heater-specific job should be done by a professional who can check the heater type, the code requirements and the connections.
Where a shower head fits in
The heater setting does not tell you how a shower head will spray or how much water it uses. For fit and spray, the shower head size guide covers the choice of head. The sources in this article do not discuss spray or flow. For mounting height, the shower head height guide is the place to look. None of these four sources addresses height.
How we chose
The four sources here were saved as text on 2026-10-28. Two are peer-reviewed journal articles hosted by PubMed Central: the Baltimore study and the Ontario study. The other two are the U.S. Consumer Product Safety Commission’s Publication 5098 and the Illinois administrative code section on hot water supply and distribution, published through Cornell Legal Information Institute. The CPSC and Cornell LII pages come from separate publishers. Retail listings, product pages and general blog posts were not used. The choice follows the question: which sources describe heater settings, policy results and valves.
What the sources do not say
- They do not give a shower-specific temperature for any heater type or household size. The Baltimore figures are for water at the homes sampled, not for a shower head.
- They do not give a national estimate for heater setting compliance. The Baltimore sample covers 976 urban homes, and the Ontario study covers one province.
- They do not explain why the New York City evaluation found no effect while the Washington evaluation did.
- The Illinois text covers water heaters used for space heating, and its valve requirement is written for that case. It is not a general rule for every water heater.
- They do not give steps for adjusting, repairing or installing any water heater, and this article does not supply them.
What we could not verify
We could not verify the current manufacturer presets for specific models, the present-day compliance rate in any city, or the cost of a mixing valve. The studies describe conditions at the time they were run, and the policy text describes the rules as written in those documents.
FAQ
Does the water heater setting control the shower temperature?
It is the main control, but not the only one. The NIH study says tank temperature is not constant, and the temperature at the tap can be affected by the pipes between the heater and the fixture.
Is 120 degrees the right setting for a shower?
The sources use 120 degrees as the reference point. The CPSC describes 120 degrees as a setting that may be necessary to reduce or eliminate most tap water scald injuries. The sources do not give a single correct number for every home.
Do electric or gas heaters perform differently?
In the Baltimore study, electric heaters were more likely than gas heaters to have safe hot water temperatures. The study also found gas heaters at 130 degrees or higher even when the gauge was set low.
What is a mixing valve?
The Illinois standard describes a thermostatic mixing valve on the hot water line to the plumbing fixtures, and Ontario requires antiscalding mixing valves in new residential buildings at the heater outlet or at each faucet. The sources describe the valve by its requirement, not by how it is built.
Who should change the heater setting?
A licensed plumber or electrician. This article does not give steps, and the CPSC text describes its own procedures in general terms only.
Bottom line
The 120 degree setting is the reference point in these sources. It is a voluntary standard for heaters, and the studies show that homes still run hotter than that. The heater dial does not fully determine the temperature at the shower. For any question about the heater, the valves or the connections, use a licensed plumber or electrician.
Sources
- U.S. Consumer Product Safety Commission, “Avoiding Tap Water Scalds,” Publication 5098. https://www.cpsc.gov/s3fs-public/5098-Tap-Water-Scalds.pdf (saved 2026-10-28)
- Ill. Admin. Code tit. 77, § 890.1220, “Hot Water Supply and Distribution,” via Cornell Legal Information Institute. https://www.law.cornell.edu/regulations/illinois/Ill-Admin-Code-tit-77-SS-890.1220 (saved 2026-10-28)
- Shields W.C., McDonald E., Frattaroli S., et al. “Still too hot: Examination of water temperature and water heater characteristics 24 years after manufacturers adopt voluntary temperature setting.” J Burn Care Res. 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3605550/ (saved 2026-10-28)
- Clouatre E., Pinto R., Banfield J., Jeschke M.G. “Incidence of Hot Tap Water Scalds After the Introduction of Regulations in Ontario.” J Burn Care Res. 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC7856629 (saved 2026-10-28)
