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AQUASTAT CONTROL Functions
CHECK VALVES, WATER SUPPLY
CLOGGED SUPPLY PIPING
DEBRIS in WATER SUPPLY, Water Heater
FLOODED HEATING EQUIPMENT REPAIR
FREEZE-PROOF A BUILDING
HEAT TAPES, Heat, Insulation prevent Freeze-Up
HOT WATER SUPPLY
HOT WATER IMPROVEMENTS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
NO HEAT - NO HOT WATER: HEATER DIAGNOSIS
NOISE, PLUMBING CHECKLIST
ODORS GASES SMELLS, DIAGNOSIS & CURE
PIPING IN buildings, Clogs Leaks Types
PLASTIC HEATER VENT
PLUMBING FIXTURES, KITCHEN, BATH
RELIEF VALVES - TP Valves on Boilers
SEWER GAS ODORS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas Detection
WATER HEATER ALTERNATIVES
WATER HEATER ANODES, DIP TUBES
WATER HEATER NOISES
WATER HEATER SCALE - De-Liming Procedure
WATER HEATER SCALE PREVENTION
WATER ODORS, CAUSE CURE
WATER PIPES, Clogs Leaks Types
WATER SOFTENERS & CONDITIONERS
Guide to hot water temperature settings & devices to avoid scalding: here we provide tables of scalding temperature and times, hot water scalding regulations and guidelines, and advice about use of anti-scalding devices to avoid dangerous, potentially fatal hot water burns. This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. See MIXING / ANTI-SCALD VALVES for our complete article series on anti-scald equipment, devices, both automatic and manual tempering or mixing valves, and their settings necessary to avoid hot water burns.
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What are safe temperatures for residential hot water?
Continue reading about anti-scald protection at How Anti Scald Valves Work.
The U.S. CDC offers this simple safety advice to avoid scalding burns at plumbing fixtures:
Our home page for anti scald devices used in plumbing systems is MIXING / ANTI-SCALD VALVES. The article below, MIX VALVE SCALD PROTECTION, Best Practices, includes excerpts or adaptations from Chapter 6 of Best Practices Guide to Residential Construction, courtesy of Wiley & Sons and written by Steven Bliss.
Watch out: it can be confusing listening to plumbers, home inspectors, and building supply sales staff who toss around terms like "mixing valve", "tempering valve", and "pressure-balancing valve" a bit loosely, all referring to ways to avoid scalding burns at plumbing fixtures, but not all working the same way.
There are several approaches to controlling hot water temperature to avoid scalding burns:
There are many styles of mixer valves in tubs and showers, but all should have some sort of protection against scalding. The young and elderly are at greatest risk due to thinner skin and slower reaction times. More than 35,000 children, most under age six, are treated each year in emergency rooms for tap-water scald burns, according to the National Safe Kids Campaign.
A child exposed to 140°F water for as little as three seconds (see Table of Scalding Temperatures & Times) can sustain a third-degree burn requiring hospitalization and skin grafts. Although most scald burns occur in the kitchen, according to the Consumer Product Safety Commission, the most severe scald burns are caused by water flowing into the tub or shower. In response, many state and local codes now require antiscald protection in residential tubs and showers.
Many organizations advocate setting water heaters to no more than 120°F, which gives bathers significantly more time to move away or adjust the temperature before a burn occurs. While this strategy is helpful, it is not always reliable and can cause other problems:
This is the most commonly used point-of-supply approach. These automatically adjust the water pressure to maintain the mix of hot and cold water to within 2°F to 3°F of where the user set the shower control.
If cold water is diverted to a flushing toilet or other appliance and the pressure drops, the valve automatically reduces the hot water flow proportionately to maintain the temperature.
If the cold water pressure plummets or stops altogether, the flow is reduced to a trickle.
To guard against someone accidentally turning the shower valve to scalding temperatures, these valves typically use a temperature limit stop that prevents the user from turning the shower control past a set point—typically set at or below 120°F.
Some models of thermostatic mixing valves are more expensive than pressure-balancing valves and not widely used in the United States. They can be installed either inline near the water heater or as part of the shower control. The inline type of valve, also called a tempering valve, adds cold water to the hot water as it leaves the water heater to maintain a constant temperature, set by the installer. These are commonly used with solar water heaters but can also be tied to a conventional water heater.
A check valve is required on the cold water side to prevent backflow, and a hot-water expansion tank is recommended to prevent excessive pressure on the hot water side.
In retrofits, point-of-use devices can be installed by a plumber or homeowner to limit water temperatures to 120°F. These include antiscald showerheads, as well as point-of-use devices that fit into individual plumbing fixtures, such as showerheads and bath and sink faucets.
For example, MemrySafe and ScaldShield (Antiscald Inc.) are inexpensive retrofit devices that reduce the water flow to less than 1/4 gallon per minute when the water temperature at the faucet or showerhead exceeds 120°F. These devices do not regulate temperature or pressure, but do offer protection against serious burns.
Frequently Asked Questions (FAQs) about hot water set temperatures, scalding hot water burn hazards, and steaming hot water faucets
Some of the FAQs discussed below are adapted from information provided by the Watts Regulator Company in a 1973 publication.
Question: when I turn on our hot water faucet steam comes out - what should I do?
I was told to open the hot water faucet to allow "excess steam" to escape from our hot water heater tank. Somehow this just doesn't sound right to me. - Living dangerously, Chicago 6/30/12
Reply: there is an immediate risk of water heater explosion
If a water heater is overheating (and thus is unsafe) the water in the tank can flash to steam when it reaches the opening of an open water faucet.
Watch out: Steam coming out of your hot water faucets indicates a very dangerous situation: your water heater tank is dangerously and seriously overheating. There are just two alternatives, and the homeowner has to choose among them by her perception of danger (history of the steam problem for example) and her mechanical expertise:
The safest step is to immediately evacuate the building - a steaming water heater is in danger of exploding.
If you feel safe and competent to do so, you or a qualified person can immediately shut off the water heater's energy source from inside or preferably outside the building. 
After the water heater has been shut down and the building found safe, call a plumber, not the one who fouled up your water heater in the first place, and ask her to have a proper temperature/pressure relief valve installed on the water heater and to check it for safe and proper settings and operation.
Should you open or leave open a hot water faucet if steam comes out? Will that prevent a water heater explosion?
Opening a hot water faucet might buy a little time by sending cold water into the water heater storage tank, but don't count on the flow rate through the piping system to be anywhere near adequate to safely release the amount of heat that would be necessary to make the system safe. Worse, you could cause the water tank to explode.
Watch out: as Watts explains, although incoming cold water might help cool down the water in an overheated water tank, the cool water suddenly impacting the bottom of an overheated water tank can cause a metal stress and a pressure-heat rupture - leading to a water tank explosion. 
Question: is it legal to have showers with no hot water temperature adjustment?
I want to know if it is legal to have showers with no way to adjust the temperature of the water. I hope you are unbiased. [At our facilities] our showers only have hot water coming out. I have RSD and my legs are extremely sensitive to hot and cold, and I can't even stand the mist if I stand back from the shower spray. Is there any law that says you have to be able to lower temps of hot water? I would think by now that there could be built in temp adjustments so there would be no handles to break. Thank you for any help you can provide.
Thank you for the question, it helps us realize where we need to work on making our text more clear or more complete. We must emphasize that an onsite inspection by a competent investigator will certainly find conditions and clues that may not yet have been observed nor reported, so any advice by remote email is of necessity incomplete and a bit theoretical. For example, if the water coming out of showers is hotter than recommended by various safety standards that would be improper. I'm not sure I can say what's legal since rules that pertain to various types of public shower facilities management may be different, but it seems reasonable to me that you could expect basic safety and health standards to apply. That apology made, here are some comments:
There are several types of automatic mixing valves that are designed to be installed on hot water supplies or right at bath fixtures (like a shower) that can be set to a particular temperature - as a safety device to avoid scalding. See the article above for a table of temperatures that suggest what hot water temperature is considered "too hot" or at risk of scalding someone.
In my OPINION, where manual adjustments to shower temperature are not provided, an automatic anti-scalding device should be in place and should be set to a safe temperature. The highest temperature permissible that will reliably avoid scalding is 100 degF.
So start by making some actual temperature measurements, documenting the temp range and the temp variation (if it does) at different times of the day.
Regarding your question of "is it legal" to have no shower temperature control, see the various codes and laws summarized in our table above - Hot Water Anti-Scald Limits: Laws & Regulations
There are plumbing and safety standards that may apply to shower hot water temperature regulation, such as
Please keep me posted on how things progress, What we both learn may help me help someone else.
As for your hope that our reply would be unbiased, InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website. We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles.
Question: too-hot water sagged plastic piping and led to a scalding burn
Home inspector did not check domestic HW temp, but noted that a 10 foot length of unsupported 2" PVC drain had a 4" dip mid length. Discovered later (after burns) HW was 150F, explaining the softening and sag of the drain pipe.
House was built in 2003 with several prior occupants. Heater was Buderus Oil indirect tank, manufacturer provides no install instructions (and does not care) or warnings (like you showed for A.O. Smith re: Aquestat selection).
The installer select a Honeywell with 140-210 range and a 15 degree differential, which means even if you checked HW temp it might be 125 now, and 150 later.
CPSC regulates gas/oil but NOT indrect heaters. Ques: Any other governing body for Mfg??? - Harvey 12/19/2012
the standards and advice for avoiding scalding burns from domestic hot water supply are in the article above. Watch out also for burst piping, leaks and related burns or leak damage where plastic water supply piping is installed on hot water heating systems and building supply.
Buderus provides several models of indirect fired water heaters, Models Buderus SST150-40, SST250-65, SST300-80, and SST450-119.
A review of the installation instructions for that equipment, available free at the company's website (see below) reaches a conclusion very different from your own about the company's concern for safety, including scalding burn hazards. The installation instructions plainly call for and show in the illustrations the installation of an anti-scald device (pointed to by the red line in the illustration above-left - click to enlarge). The following is a direct quotation from that document:
See AQUASTAT CONTROL Functions for a discussion of that heater temperature control and how it affects heat from a tankless coil
For information about Buderus Heating Equipment contact Buderus USA, Bosch Thermotechnology, 50 Wentworth Avenue, Londonderry NH, 03053, Tel: 603-552-1100, Toll Free: 800-283-3787, Website: http://www.buderus.us/
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