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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 PLEXVENT ULTRAVENT RECALL
PLUMBING FIXTURES, KITCHEN, BATH
RELIEF VALVE, TP VALVE, BOILER
SEWER GAS ODORS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCH, FLUE GAS DETECTOR
WATER HEATER ALTERNATIVES
WATER HEATER ANODES, DIP TUBES
WATER HEATER NOISE DIAGNOSIS, CURE
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.
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What are safe temperatures for residential hot water?
This photo of the warning labels on an A.O. Smith gas fired power-vented domestic hot water heater includes text warning consumers about serious burn hazards and even death from exposure to water that is too hot.
(Click on the photo to enlarge and read the text more easily).
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:
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 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.
See ANTI SCALD VALVES / MIXING 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.
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.
The unit will compensate for changes in either pressure or temperature to maintain a constant delivery temperature and flow rate.
If the cold water fails or the tempered water is still too hot for any reason, the unit will shut off the flow.
As with the pressure-balancing valve, the installer sets a temperature limit stop to prevent the user from turning the shower control to scalding temperatures.
We illustrate this approach as it is installed in a modern bathroom in Molde, Norway at BUILT-IN FIXTURE ANTI-SCALD VALVES.
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.
This table has been moved to HOT WATER ANTI-SCALD REGULATIONS
Suggested citation for this web page
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Frequently Asked Questions (FAQs)
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.
Reply:In addition to the scalding temperature data given in the article above,
Regarding your question of "is it legal" to have no shower temperature control, see the various codes and laws found at HOT WATER ANTI-SCALD REGULATIONS .
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/
Question: Does federal law limit washing machines to 120°F?
(Feb 21, 2014) Anonymous said:
We can only get warm water (no hot) in the washers in the laundromat at my apt complex. The manager says "Federal law requires that water temp for washing machines be no hotter than 120 degrees". True or BS?
True (though as a building code not a "federal law"), but not exactly.
Water should not be hotter than 120°F AT THE POINT OF USE as there would be a serious risk of scalding burns.
For sake of illustration and EMPHASIZING that I am NOT describing your building, for which we have no data, water could be set at 120F at the water heater, which would be safe, but if the water has long pipe runs through the building it could be arriving at much lower temperatures.
Solutions to this problem vary: some buildings use a continuous circulating hot water loop so that everybody gets hot water quickly; some use point-of-use water heaters; some send much hotter water through the building but install anti-scald devices at each fixture.
Question: New Hampshire apartment gives water that is unbearably hot
(Feb 26, 2014) TeeWee said:
I live in an apartment in NH, and the water that comes out of the kitchen sink is unbearably hot. I usually remember to keep the faucet in the middle range when washing dishes, but quite often, it will suddenly get hot fast, and I get scalded. This happens ALL the time. And now, I used a thermometer to see what the temperature was, and it was 150 degrees! I did this a few times and with two different thermometers, and it was the same thing. I have a six year old, and while I don't let him play in the sink, he was washing his hands and he got scalded too. Do I have a right to ask the property managers to turn down the temperature? No one else in the building seems to have a problem with the temperature being that high. I just moved in a few months ago, and I don't want to be the tenant that ruins the hot water for the people who seem to like it like that. Thoughts?
The temperature you cite is above the common 120°F standard and more important, it's unsafe and is a scalding hazard. (States vary in the codes and standards they have accepted, and allowable temperatures vary as well, with some such as CA being the lowest (105deg). No one recommends allowing hot water to be delivered at the tap at the high temperature that you cite.
New Hampshire has adopted the IPC which sets a maximum temperature of 120F - as you can read in the table in the article above. You are welcome to print and attach the InspectApedia article on scalding temperatures to your letter to your management.
You can view the NH building codes at www.nh.gov but that should not be necessary to address this safety concern.
Notify the property owners and managers immediately by telephone and in writing.
The solution may be to regulate the temperature of hot water at the source or by regulating hot water temperature at individual apartments at the point of hot water entry, or by the installation of anti-scald devices at each plumbing fixture (the most troublesome and costly approach).
WATCH OUT: the time to receive a SCALDING BURN at 150F, the temperature you cite, is basically instant! And it's not just you. You know that the water can be scalding. But a visitor to the building, or perhaps in your case a babysitter, unfamiliar with the local building's unsafe water temperatures, could easily be scalded.
Question: Condominium is delivering 150F hot water - is this allowed?
(Feb 28, 2014) FingerOfFate said:
I live in a condo building where all units share a single boiler for both heat and hot water. There are a mix of owner occupied units and rental units. Recently, water as hot as 150 degrees or more regularly comes out of the faucets. The building management company responded to my concerns about the unit owners' liability for scalding injuries garnered a response telling me to put an anti-scalding device on my shower.
Built in the 70's, most of the units predated the building code requiring these devices. I am assuming that there is a grandfather clause that does not compel any owners to put in such devices in individual units at this point. And if we can not compel them all to do so, I think any liability would fall on the Condo Association- i.e. all of us that own units.
The management company tells me that the current mixing valve used on the main boiler has only two possible temperature settings; one that outputs water between 110 and 160 degrees (the current setting) and the other that sends out water between 70 and 110 degrees.
With that as background, I have 3 questions:
1. Do the regulations for maximum temperatures only apply to water in showers, or do the regs apply to all sinks, in all rooms?
2. Assuming the answer is "all," wouldn't the smart thing be to install a better mixing valve with tighter temperature variations and a more appropriate temperature range rather than worry about individual units' showers?
3. What is the typical range of temperature variation expected at the output of a main boiler mixing valve such as the one currently in use here?
1. Since one can be scalded at any fixture, the scalding concern applies to all fixtures, not just showers; there may be special shower regulations for some circumstance (such as prisons)
2. Not necessarily; building size, piping layout, and the need to get hot water to everyone may be reasons for regulating hot water at individual points of use; that's what manufacturers and industry recommend (no surprise)
3. Typically a residential heating boiler operates between around 120 F in summer and 180 to 200°F during a call for heat. That does not mean that water reaching fixtures having been heated by a tankless coil or an indirect water heater will be at those temperatures.
The mixing valve or tempering valve at the boiler is what is set to regulate the outgoing temperature at that location;
A tempering or mixing valve will generally be accurate +/- 3 deg F of its set point.
Question: what is the maximum temperature for bath water?
3/17/2014 sally chettleburgh said:
council are saying we can only have or bath water temp set at 40 degrees they say its law is this right
Sally, 4°C is about 104° F - below scalding; you can read the various anti-scald temperature limits in the tables above. "Law" is most likely referring to your local or state or provincial building authorities who indeed have just that - authority. But I'm not sure who "council" refers to in your note.
Question: California regulation on maximum hot water temperature
3/20/2014 Renee goodwin said:
For apartments in California what is the law and the code for the minimum and maximum water heater temperature
First let's separate maximum water heater temperature (set by the manufacturer for the device) and maximum safe hot water temperature delivered at the plumbing fixture such as a sink or shower - where we need to avoid scalding burns in California as well as everywhere else.
For a variety of reasons, including recent interest in reducing the development of Legionnaire's bacteria in water heaters, the water heater temp will generally be quite a bit higher than the delivered hot water temperature at the fixture.
In our table above we show data for California as follows:
Questions & answers or comments about scalding, hot water burns, steaming water faucets.
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