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Mobile ViewWATER HEATERS AGE of WATER HEATERS AIRBOUND HEAT SYSTEM REPAIRS ALTERNATIVE HOT WATER SOURCES Electric Shower Heaters High Efficiency Water Heaters Indirect-fired Water Heaters Instantaneous Water Heaters Multiple water heaters in parallel Multiple water heaters in series Range Boiler Water Heaters Side Arm Coil Water Heaters Solar Water Heaters Tankless Coil for Hot Water Tankless Water Heaters ANODES & DIP TUBES on WATER HEATERS ANTI SCALD VALVES Define Mixing Valves, Anti Scald Valves Table of Scalding Temperatures & Times Hot Water Anti-Scald Regulations How Anti Scald Valves Work Installing & Setting Anti-Scald Valves Which Way To Turn the Mixing Valve Using a Manual Hot Water Tempering Valve Built-in Fixture Anti-Scald Valves Mix Valve Improves Hot Water Quantity Inspect Anti-Scald Valves ANTI SCALD VALVE PROTECTION, Best Practices Water Pressure-Balancing Valves Thermostatic Mixing Valves Retrofits to Avoid Scalding Burns APPLIANCE EFFICIENCY RATINGS AQUASTAT CONTROL Functions BACKDRAFTING HEATING EQUIPMENT BACKFLOW PREVENTERS BACKUP HEAT for HEAT PUMPS BLEVE EXPLOSIONS BOILERS, HEATING CARBON MONOXIDE - CO CHECK VALVES CHEMICAL CONTAMINANTS in WATER CHIMNEY INSPECTION DIAGNOSIS REPAIR CLOGGED SUPPLY PIPING CROSS CONNECTIONS, PLUMBING DEBRIS in WATER SUPPLY, Water Heater DRAIN a WATER HEATER TANK ELECTRIC WATER HEATERS Electric, Gas, Oil Water Heater Efficiency Electric Shower Heaters Electric Water Heater Checklist Electric Water Heater Controls List Electric Water Heater Element Replacement Electric Water Heater Element Tests Electric Water Heater High Temp Cutoff Test Electric Water Heater Repair Guide Electric Water Heater Reset Switch Electric Water Heater Thermostats Electric Water Heater No Hot Water Electric Water Heater Parts Identification Electric Water Heater Reset & Temp Set Hot Water Temperature & Pressure Valve Timers for Electric Water Heaters Water Heater Anode & Dip Tube Check ENERGY SAVINGS in buildings FLOODED HEATING EQUIPMENT REPAIR FLOODED WATER HEATER REPAIR FREEZE-PROOF A BUILDING FROST HEAVES, FOUNDATION, SLAB GALVANIC SCALE & METAL CORROSION GAS BURNER Flame & Noise Defects GAS FIRED WATER HEATERS DRAFT HOODS - gas fired Gas BTUH & Cubic Feet Gas Conversion LP Natural Gas GAS PIPING, VALVES, CONTROLS SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection GAS PIPING, VALVES, CONTROLS HEAT TAPES, Heat, Insulation prevent Freeze-Up HEATING COST FUEL & BTU Cost Table HEATING COST SAVINGS METHODS HEATING SYSTEMS HOT WATER SUPPLY HOT WATER IMPROVEMENTS HOT WATER DELIVERY SPEED UP HOT WATER PRESSURE EXPANSION RATE HOT WATER PRESSURE LOSS HOT WATER QUANTITY IMPROVEMENT Alternative Hot Water Sources & Methods Anti-Scald Valves & Hot Water Quantity CLOGGED PIPING & Hot Water Flow Extra Tanks to Increase Hot Water Insulate Hot Water Piping Insulate Hot Water Tank? Larger Diameter Water Supply Piping Water pipe clog diagnosis Water pipe clog repair guide HYDROGEN SULFIDE GAS INDIRECT FIRED WATER HEATERS MANUALS & PARTS GUIDES - HVAC MIXING / ANTI-SCALD VALVES NO HEAT - NO HOT WATER: HEATER DIAGNOSIS NOISE / SOUND DIAGNOSIS & CURE NOISE CONTROL for HEATING SYSTEMS NOISE, PLUMBING CHECKLIST NOISES, WATER HEATER ODORS & SMELLS DIAGNOSIS & CURE ODORS GASES SMELLS, DIAGNOSIS & CURE ODORS IN WATER OIL FIRED WATER HEATERS PIPING IN buildings, Clogs Leaks Types PLASTIC HEATER VENT RADIANT HEAT RANGE BOILERS RELIEF VALVES - TP Valves on Boilers RELIEF VALVES - Water Heaters RELIEF VALVES - Water Tanks SAFETY, HEATING INSPECTION SCALE REMOVAL, WATER HEATERS SEWER GAS ODORS SOLAR ENERGY SYSTEMS SOLAR HOT WATER HEATERS SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection TANKLESS COILS AQUASTAT CONTROL Functions Clogged Pipes / Tankless Coil De-Scale MIXING / ANTI-SCALD VALVES Tankless Coil Conversions Tankless Coil Leaks Tankless Coil Hot Water Increase TANKLESS WATER HEATERS Electric Shower Heaters Guide to Tankless Water Heaters Operation & Characteristics Problems & Defects Hot Water Delivery Speedup Installation Requirements & Costs Should I Convert to a Tankless Heater? Calculate Water Heater Requirements Capacities of Tankless Water Heaters Life Expectancy & Applications Temperature Pressure Relief Valves - Water Heaters THERMOSTATS, HEATING / COOLING THERMOSTATS, WATER HEATER AQUASTAT CONTROL Functions Electric Water Heater Thermostats TIMERS for ELECTRIC WATER HEATERS VALVES, PLUMBING WATER CONTAMINANT LEVELS WATER HAMMER NOISE DIAGNOSE & CURE WATER HEATERS WATER HEATER ALTERNATIVES WATER HEATER ANODES, DIP TUBES WATER HEATER AIR INLET WATER HEATER DEBRIS FLUSH WATER HEATER DRAIN PROCEDURE WATER HEATER FLUSH PROCEDURE WATER HEATER NOISES WATER HEATER PROPERTIES Electric, Gas, Oil Water Heater Efficiency Water Heater Life Expectancy Comparisons Water Heater Operating Cost Comparisons Water Heater Purchase & Maintenance Costs Water Heater Water Quantity Comparisons Water Heater Recovery Speed Comparisons Water Heater Safety Comparisons WATER HEATER SCALE - De-Liming Procedure WATER HEATER SCALE PREVENTION WATER HEATER SAFETY WATER HEATERS for HOME HEATING USE? WATER ODORS, CAUSE CURE WATER PIPES, Clogs Leaks Types WATER PRESSURE & FLOW MEASUREMENT WATER PRESSURE VARIATION CAUSES WATER PRESSURE TOO HIGH: DANGERS Definition of Static Water Pressure Definition of Dynamic Water Pressure Measure Municipal Water Pressure Measure Pump & Well Water Pressure WATER FLOW RATE MEASUREMENT HOT WATER PRESSURE EXPANSION RATE WATER PRESSURE GAUGE ACCURACY WATER PRESSURE LOSS DIAGNOSIS & REPAIR WATER PRESSURE REDUCER / REGULATOR WATER PRESSURE REPAIR GUIDE - WELLS WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS WATER PUMPS & WELLS WATER PURIFIERS WATER QUALITY TESTS, CONTAMINANTS, TREATMENT WATER QUANTITY IMPROVEMENT WATER SOFTENERS & CONDITIONERS WINTERIZE A BUILDING More Information |
Here we explain how to buy, install, adjust and inspect anti-scald equipment to prevent hot water burns. We explain what a mixing valve, tempering valve, or anti-scald valve is, where and why these valves are installed on hot water systems, and how they work. InspectAPedia offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/Contact.htm.If your hot water temperatures are too low, see Temperature of Hot Water is Too Low This website 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. © Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. Guide to Mixing Valves and Anti Scald Valves on Heating Equipment & Plumbing FixturesDefinition of an anti scald valve or compensating valve used to avoid hot water burnsAnti-scald valves are used on heating and plumbing systems to avoid hot water burns at plumbing fixtures such as sinks, showers, and tubs. An anti-scald or mixing valve mixes cold water with the outgoing hot water either automatically or manually to make sure that a person using the plumbing fixture won't be scalded. We describe and illustrate various types of automatic and manual mixing valves, anti-scald valves, or compensating valves in this article. Sources of hot water scald burn risk at buildings without adequate anti-scald device protectionWatch out: Where no anti-scald valve is installed, the risk of a person being badly burned by hot water can be significant in buildings for a variety of reasons that we will explain here, including:
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. Approaches to controlling hot water temperature to avoid scalding burnsThe high temperature limit control on the water heating device itself can be set to prevent scalding water from being produced. Below at Table of Scalding Temperatures & Times we include a photo of a typical water heater label warning about scalding temperatures, implying that this option is one to consider. A point of supply pressure balancing valve or automatic mixing valve (compensating valve, or a manual mixing valve) can be installed at or near the water heater, or at the tankless coil or other hot water source so that scald protection is provided even if the water heater is set to a high temperature. This approach is sometimes used to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT.
An temperature-sensing thermostatic mixing valve or anti-scald device can be installed at or near the water heating device so that even if the water heater is set to a high temperature (to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT).
In our photo a Honeywell limit control switch is being used to monitor hot water temperature at the tankless coil which is in turn mounted on a steam boiler of an older home in Portland, Maine. You can see the black-handled mixing valve in the lower right of this photo. Cold water from the building is entering the tankless coil via the bottom pipe (green corrosion) and hot water, heated by the coil is leaving at the upper part of the tankless coil, where it turns downwards to enter the left side of the mixing valve. Additional cold water is permitted to enter the bottom of the mixing valve, and tempered (non-scalding) hot water then leaves at the right side of the mixing valve in this photo. In this picture of a more traditional single-function heating boiler limit control, the limit switch is being used on a tankless coil, and in the enlarged version of the photo you'll see that the temperature limit on the control is set to about 140 degF. Below we show a sketch that explains how an anti-scald valve or tempering valve actually works. Tables of Scalding Temperatures & Exposure Times that Cause Hot Water Burns, Laws, Regulations.See Table of Scalding Temperatures & Times for a table of safe temperatures for residential hot water. See Hot Water Anti-Scald Regulations for a table of Hot Water Anti-Scald Limits, Hot Water Anti-Scald Laws & Hot Water Regulations How Automatic Anti Scald Valves, Mixing Valves, or Tempering Valves on Water Heaters Work
The 180 deg .F. water leaving the tankless coil is mixed with 55 degF. water inside the tempering valve. This produces outgoing hot water from the valve cooled down to 140 deg F. In the U.S. most authorities consider hot water at or below 120 deg F to be safe from scalding. Some facilities limit water temperatures to 100 deg. F. Automatic vs. Manual Mixing Valves Work Differently and are Not Equally SafeAn automatic mixing valve or compensating valve such as those sold by Watts Regulator Co. or Sparco (and illustrated below) includes a temperature sensing mechanism that automatically adjusts the amount of cold mixed in with outgoing hot water to maintain the desired output water temperature. A manual mixing valve such as those often installed at older tankless coil hot water systems uses a simple gate valve that is manually adjusted by the homeowner. At a minimum the homeowner may have to adjust this valve seasonally depending on whether or not the building is also being heated by the same boiler as during the heating season the boiler will be kept hotter than during the rest of the year, making the outgoing hot water too hot. Guide to Installing & Setting Automatic Anti-Scald Tempering or Mixing Valves at a Tankless Coil - Water Pressure Balancing TypeWhich Way do We Turn the Anti-Scald or Automatic Mixing Valve to Make Hot Water Cooler or Hotter?Question about tankless coil or other hot water mixing valve operation - example using the Sparco Aquamix AM 102C:
Answer:There should be a direction arrow on the anti-scald valve telling you what it is doing and which turn direction will raise or lower the outgoing water temperature. The Sparco Aquamix AM 102C tempering valve shown (above-left) is marked to explain that if we turn this valve counterclockwise (the direction of the red arrow) the outgoing water temperature will be hotter. Turn this anti-scald valve (and most model) clockwise (in the direction of the blue arrow) to make the outgoing water temperature cooler. Our photo of a Sparco™ Aquamix AM102C anti-scald or tempering valve (above-left) as well as our photo of a Watts™ mixing valve shown earlier in this article both show the arrow that we describe and indicates that turning the automatic mixing valve knob clockwise makes the outgoing water cooler, and turning the automatic mixing counterclockwise makes the outgoing water hotter. We don't describe the valve direction as "up" or "down" because these valves can be installed in more than one position, making "up" and "down" a bit confusing. For hotter output water [on the Sparco or Watts Tempering Valve models shown]: Turn the automatic mixing valve knob counter-clockwise (on the Sparco valve above, in the direction of the red arrow) to make the output water from the system hotter. For cooler output water: Turn the automatic mixing valve clockwise (on the Sparco valve above, in the direction of the blue arrow) to mix in more cold water and thus to make the output water from the system cooler. Note that because these mixing valves are automatic, that is once they have been set they maintain a specified hot water temperature for water leaving the water heater, you don't have to make seasonal changes to the valve adjustment. The automatic mixing valve, tempering valve, or anti-scald valve approach of installing this safety control at or close to the water heater is discussed further at Thermostatic Mixing Valves. Watch out: Be sure to take a close look at the indicating arrows on your own automatic mixing valve as some tempering valve models may work differently. And for manual hot water mixing valves that we discuss below, the direction to turn the valve may not be marked, but is easy to determine, as we will explain. Thanks to readers Bruce Jones and Chris Martino and others for pointing out the need for clarity about about which way to turn the hot water mixing valve or tempering valve. If your automatic tempering or hot water mixing valve has different instructions or operates differently from those discussed here, CONTACT us and send along a photo so that we can add that information here. Guide to Using a Manual Hot Water Tempering Valve on the Domestic Hot Water Supply
This valve must be adjusted by the building occupant to obtain the desired temperature. Our photo (left) shows a manual mixing valve (a gate valve) that is opened to add cold to outgoing hot from the tankless coils water heater. The valve in the center-right of the photo allows cold water to be added to the hot water leaving the coil. (The copper pipes were painted white - don't ask.) A manual tempering valve does not respond to changing conditions on its own. Which Way to Turn a Manual Anti-Scald Valve or non-Automatic Mixing Valve to Control Hot Water TemperatureBy "manual" mixing valve we mean that an ordinary plumbing valve, usually a gate valve or ball valve is used to adjust outgoing hot water temperature, and the building occupants have to adjust the valve by hand, "manually". In most cases a manual hot water mixing or tempering valve (discussed below) will work oppositely from many models of the automatic tempering valves discussed above. On a manual mixing valve or "tempering valve" if we "close" the manual valve by turning it clockwise we are are admitting less cold water into the mixing process, thus making the output water temperature hotter at plumbing fixtures in the building.
Guide to Bath Fixture Anti-Scald Valves, Thermostatic Mixing Valves, or Tempering Valves to Avoid Hot Water Burns
How Can an Anti-Scald Valve Improve the Hot Water Volume & Quantity?Using an anti-scald valve or "mixing valve" or "tempering valve" on a hot water supply system can increase both the actual and the apparent total quantity of hot water available. That is, building occupants get a longer time in the shower, provided the hot water is used with some sense, as we explain here. We will have more "heat" stored in the hot water tank (or more heat stored inside the heating boiler that in turn is going to heat a tankless coil and thus heat water passing through the coil) if we can keep the hot water tank (or boiler) at a higher temperature. Watch out: when we heat the hot water tank or boiler to a higher temperature we also increase the chances of someone being scalded at the tap. Therefore, to avoid scalding, we mix cold in with the outgoing hot water (the right way to do this). Where a mixing valve is not installed (watch out for scalding!) we can be smarter at the plumbing fixture itself by turning on less hot water flow and more cold water flow so that the water is not scalding. This combination of keeping water in the hot water tank (or boiler) hotter, but causing the volume of hot water to flow more slowly at the individual plumbing fixture, mixing in enough cold to get adequate flow quantity and safe temperature, is a risky (scald risk) alternative to using a mixing valve. We don't recommend this alternative, (see MIX VALVE SCALD PROTECTION, Best Practices) but we explain it here as you may encounter this approach, especially in an older building and one where there are no small children nor elderly occupants (who are at greater risk of being scalded). In either case, by starting with a hotter water heater or boiler and by mixing in cold in the outgoing water (or by regulating water pressures at the fixture), we consume hot water in the water heater tank more slowly. That means longer time in the shower. In sum, with careful installation of appropriate safety controls such as an automatic mixing valve or automatic tempering valve (or by careful use of a manual mixing valve), we can heat water in the water heater storage tank or tankless coil to a higher temperature, mixing or tempering it as it leaves the water heater or at the point of use in the building to avoid scalding. The result is more total hot water available from the same water heating equipment. Details about various ways to get more hot water or better hot water pressure and flow are at HOT WATER IMPROVEMENT where we provide a detailed guide to improving hot water quantity and flow when a tankless coil is installed as well as using other methods of hot water heating. Watch out: setting water heater temperature higher to attempt to obtain more total hot water at the plumbing fixtures without also installing and properly setting anti-scald devices can result in dangerous, even fatal hot water scalding burns. How do we Inspect Mixing Valves or Anti-Scald or Tempering ValvesSafety First: assure that the mixing valve has been set to protect the building occupants from scalding. Remember that while these valves may show a target temperature on the valve setting knob, the actual water temperature that comes out of a building faucet or tap will vary and may be hotter or cooler than the actual temperature set. This is not precise lab-grade equipment capable of controlling water temperature precisely, and more, the length of pipe run between the hot water source and the building faucet or fixture will affect the temperature of water received there. A long run of un-insulated hot water pipe will deliver cooler water than a well-insulated water supply pipe of any length. Leaks Second: See Tankless Coil Leaks for a detailed discussion of how to recognize, evaluate, and repair leaks at tankless coils on heating boilers Best Practices Guide to Scald Protection for Bathrooms, Tubs, ShowersOur 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: The high temperature limit control on the water heating device itself can be set to prevent scalding water from being produced. Below at Table of Scalding Temperatures & Times we include a photo of a typical water heater label warning about scalding temperatures, implying that this option is one to consider. A point of supply pressure balancing valve or automatic mixing valve (or a manual mixing valve) can be installed at or near the water heater, or at the tankless coil or other hot water source so that scald protection is provided even if the water heater is set to a high temperature. This approach is sometimes used to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT. An temperature-sensing thermostatic mixing valve or anti-scald device can be installed at or near the water heating device so that even if the water heater is set to a high temperature (to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT). As noted in Chapter 6 of Best Practices Guide to Residential Construction: 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: Noncompliance: many homeowners turn the thermostats up to increase supply. Water heater thermostats are often inaccurate. The ANSI standard for gas water heaters allows the temperature to vary by plus-or-minus 10°F. Stacking effect: water at the top of a gas water heater can exceed the set point by as much as 30°F. Use of Point of Supply Water Pressure-Balancing Valves to Control Temperature & Avoid Scalding
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. Use of Point of Supply or Point of Use Thermostatic Mixing Valves to Avoid Scalding BurnsSome 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.
Retrofits to Avoid Scalding Burns at Plumbing FixturesIn 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. Questions & Answers regarding this articleQuestions & answers about anti scald devices and mixing valves on hot water systems Ask a Question or Search InspectAPediaHTML Comment Box is loading comments...
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