anti-scald-shower-valve
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An anti scald shower valve is a shower mixing valve that controls how hot the water at the shower outlet can get. The ASSE International guidance says that shower valves of this kind “shall be automatic temperature and/or pressure compensating valves intended to be installed at an individual shower or tub/shower combination.” The same guidance says the temperature limit stop “must be set at the time of installation, and may need to be periodically adjusted for variations in water temperatures.” The two sources used here explain what the valve is for and when its setting matters. They do not give a procedure for setting the limit stop on any particular valve.
Quick answer
- The limit stop sets the valve’s temperature ceiling. The guidance says it must be set when the valve is installed.
- The guidance says these shower valves “provide both scald and thermal shock protection.”
- Hot tap water is a known source of scald injury. The ASSE guidance says: “Hot water from the tap accounts for more than 25 percent of all scald burns in children.”
- The sources do not say how to adjust a limit stop. Manufacturer instructions cover that, and valve installation is work for a licensed plumber.
Why the temperature ceiling matters
The NIH study gives the scale of the problem: “tap water scald burns cause an estimated 1,500 hospital admissions and 100 deaths per year in the United States.” Its background section adds the time element: “Human exposure to hot water at 140°F can lead to a serious burn within 3 seconds, whereas at 120°F a serious burn takes about 10 minutes.” The same section says the severity of a tap water scald “depends on the temperature of the water and the length of time the skin is exposed.”
The NIH study measured water heaters and household water temperatures, not shower valves. Its headline result is that “Hot water temperature was unsafe in 41% of homes” using the study’s own definition of safe as 120°F or below. That finding is a reason to check the temperature the water actually reaches, but it does not measure how any shower valve performed.
What a shower valve of this type is meant to control
The ASSE guidance says these valves “are intended to control the water temperature to wall- or ceiling-mounted” outlets. It lists hand-held showers, shower heads, body sprays, and tub spouts that are part of a tub/shower combination fitting.
The guidance also sets out the layout the valve should follow. It says “The user has access to flow and/or final temperature controls. No further mixing occurs downstream of the device.” In other words, the shower valve is the last point where hot and cold water are mixed before the bather. The guidance’s matrix labels this location “Point of use”.
The guidance names three types of shower valve that meet its standard: pressure balancing, thermostatic (mechanical and electronic), and a combination of pressure balancing and thermostatic. The saved text does not say which type a given shower has, and it does not say how a homeowner can tell from the outside whether a limit stop is present.
Where the protection can fall short
The guidance includes a condition on the shower head. It says “The showerhead flow rate must not be less than the manufacturer’s published minimum flow rate for the valve (device).” A head that flows below the valve’s published minimum falls outside the condition the valve is listed for. The guidance gives no number for any valve, so the valve’s own instructions are the source to check.
The guidance also covers devices that look similar but do a different job. A device listed to the ASSE 1017 standard is meant for the hot water distribution system. The guidance says that installing a device listed to ASSE 1017 “at the water heater will not provide adequate scald protection.” A setting at the water heater therefore does not replace a limit stop on the shower valve.
Some devices protect against scalds but not against thermal shock. The guidance states this for a group of devices that reduce flow when water gets too hot: “These devices provide scald protection ONLY, and DO NOT provide thermal shock protection.” The same group is described this way: “During the five (5) second response period, the bather may be exposed to temperatures in excess of the set point of the device.” A reader comparing products should check which standard a device is listed to, not only the word “anti-scald” on the packaging.
Devices the guidance compares
The ASSE guidance includes a matrix that shows, for each standard, the protection it gives and where it is installed. The table below copies the matrix’s own columns for the rows that matter most here. It is a reference from the guidance, not a ranking of products.
| Standard (as listed in the guidance) | Scald protection | Thermal shock protection | Installed at |
|---|---|---|---|
| ASSE 1016, individual shower or tub/shower valve | YES | YES | Point of use |
| ASSE 1017, hot water distribution | NO | NO | At, or near, source |
| ASSE 1062, flow reduction device | YES | NO | Point of use |
| ASSE 1066, pressure balancing in-line | NO | YES | Ahead of the control valve(s) |
| ASSE 1069, automatic temperature control | YES | YES | Where the bather has no access to the temperature adjustment means |
| ASSE 1070, water temperature limiting | YES | NO | Near, or integral to, plumbing fixture fittings |
For an individual shower, the guidance points to the 1016 row. The 1069 row covers devices the guidance describes as “Typically installed for gang (multiple) showers and sitz baths,” and it states that they are “NOT intended for individual showers or tub/showers.” Each device should be checked against its own listing.
What to check on the valve and the water
The guidance says the temperature limit stop “may need to be periodically adjusted for variations in water temperatures.” It does not give an interval. A reader who wants to know when to recheck should look for the answer in the manufacturer’s instructions for the valve, because the sources say adjustment methods depend on the manufacturer.
The guidance also states that a device “does NOT negate the requirement” for the point of use valve. That is the reason the shower valve still matters when a water heater or distribution device is in place, and the reason the two should not be treated as one step.
How we chose
This article uses two sources. The ASSE International guidance is a standards-body paper that sorts temperature control devices by standard, and it is the source for the shower valve rules quoted above. The NIH study is a peer-reviewed paper in the Journal of Burn Care Research, and it is the source for the scald figures and for the 120°F reference. Both were opened on 2026-10-28, and their saved text was checked against every quote used here.
The article does not rank products and does not name brands or models. Neither source compares retail products, so the article does not either.
What the sources do not say
- How to adjust the limit stop on any valve. The guidance does not describe the method and points to the manufacturer’s instructions.
- Which shower valve or head to buy, or whether one brand is better than another. The guidance does not make that judgment.
- The price of an anti scald shower valve or of its installation. The NIH study does not give a shower valve price.
- How often a limit stop should be rechecked in a given home. The guidance gives no interval.
- Whether any specific product meets the ASSE 1016 standard. No product was checked.
What we could not verify
The two sources do not give the local code requirement for any city or state. The guidance says the authority having jurisdiction has the final approval of installations, so the local rule must be confirmed with that office. The NIH study covers 976 urban homes in one study period and does not report how many of those homes had a shower valve with a limit stop. Its figures come from water heater data and are not a shower valve test.
FAQ
Is an anti scald shower valve the same as a pressure balancing valve?
Not necessarily. The ASSE guidance lists pressure balancing as one of three types of shower valve that meet its standard, alongside thermostatic and a combination of the two. The valve’s listing or instructions show which type a given product is.
What maximum temperature do the sources give?
The NIH study says that thermostatic mixer equipped valves “limit water temperature to a maximum of 120°F.” The ASSE guidance defines hot water as water at a temperature of not less than 120° F. The limit a home must meet is set by local code, which the guidance says the authority having jurisdiction applies.
Can a homeowner change the limit stop?
The guidance says the limit stop must be set at installation and may need periodic adjustment. It does not describe how. The manufacturer’s instructions for the valve are the place to look, and any adjustment should follow them.
Does an anti scald valve prevent every scald?
The sources do not say so. They describe a valve that controls temperature at the outlet when it is installed and set correctly. The guidance warns that installing the wrong device “can lead to a false sense of security by the ultimate user.”
Does a water heater setting replace a shower valve?
The guidance says no. A device listed to ASSE 1017 installed at the water heater “will not provide adequate scald protection.” It is a distribution device, and the guidance says it does not negate the point of use requirement.
Who should install or replace a shower valve?
The sources do not give installation steps. Valve installation is work for a licensed plumber, and the authority having jurisdiction approves the installation. A plumber can also confirm the valve type and whether a limit stop is present.
Bottom line
An anti scald shower valve is only as useful as its temperature ceiling. The guidance’s main rule is that the limit stop must be set at installation and may need adjustment as water temperatures change. Check the valve’s instructions, confirm the setting was made, and leave installation to a licensed plumber.
Sources
- ASSE International Scald Awareness Task Group. “Guidelines for Temperature Control Devices in Domestic Hot Water Systems.” White paper. https://asse-plumbing.org/media/pbfltxqk/asse_guidelines_for_temp_control_devices.pdf (opened 2026-10-28)
- Shields WC, 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;34(2):281-287. https://pmc.ncbi.nlm.nih.gov/articles/PMC3605550/ (opened 2026-10-28)
