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 Mobile View HEATING SYSTEMS ANTI SCALD VALVES BOILERS, HEATING BOILER OPERATION DETAILS BOILER CONTROLS & SWITCHES Air Bleeder Valves Aquastat Functions BOILER LEAKS CORROSION STAINS BOILER OPERATING PROBLEMS BOILER PARTS LIST Boiler Pressure Controls & Settings Cad Cell Relay Switch Flame Sensors Circulator Pumps & Relays Draft Regulators, Dampers Expansion Tanks Gauges on Heating Equipment Limit Switches, Boilers Mixing Valves Relief Valves - TP Valves Reset Switch - Primary Control Reset Switch - electric motors Spill Switches Stack Relay Switch Thermostats Water Feeder Valves, Hydronic Boiler Zone Valves CARBON MONOXIDE/DIOXIDE CARBON MONOXIDE WARNING CHIMNEY INSPECTION DIAGNOSIS REPAIR CHIMNEYS & Flues - Asbestos Transite Pipe COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ DEFINITION of Heating & Cooling Terms DRAFT HOODS - gas fired DRAFT REGULATORS - barometric dampers DUCT SYSTEMS DUCT INSULATION, Asbestos Paper DUCTS, Asbestos Transite Pipe DUST FROM HVAC? ELECTRIC HEAT ELECTRICAL POWER SWITCH FOR HEAT ENERGY SAVINGS in BUILDINGS ENERGY SAVINGS PRIORITIES ENERGY SAVINGS RETROFIT CASE STUDY ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE ENERGY SAVINGS RETROFIT OPTIONS FAN CONVECTOR HEATERS - HYDRONIC COILS FLUE VENT CONNECTORS FREEZE-PROOF A BUILDING FURNACES, HEATING DUCT SYSTEM DEFECTS DUCT & AIR HANDLER ODORS FAN LIMIT SWITCH FURNACE CONTROLS & SWITCHES FURNACE OPERATION DETAILS HEAT EXCHANGER LEAKS STACK RELAY SWITCHES GAS PIPING, VALVES, CONTROLS GAUGES ON HEATING EQUIPMENT HEAT LOSS in BUILDINGS HEAT LOSS DETECTION TOOLS HEAT LOSS INDICATORS HEAT LOSS PREVENTION PRIORITIES HEAT LOSS R U & K VALUE CALCULATION HOUSEWRAP AIR & VAPOR BARRIERS HEATING COST SAVINGS METHODS HEATING LOSS DIAGNOSIS-BOILERS HEATING LOSS DIAGNOSIS-FURNACES HEATING OIL CLOUD WAX GEL POINT HEATING OIL EXPOSURE HAZARDS, LIMITS HEATING OIL SLUDGE HEATING SMALL LOADS HEAT PUMPS HEATING SYSTEM INSPECTION PROCEDURE HOT WATER HEATERS HOT WATER IMPROVEMENT INSULATION & VENTILATION INSPECTION & IMPROVEMENT MIXING VALVES NO HEAT - BOILER / FURNACE DIAGNOSIS OIL BURNERS OIL BURNER INSPECTION GUIDE OIL BURNER NOISE SMOKE ODORS OIL BURNER SOOT & PUFFBACKS OIL FUEL TYPES & CHARACTERISTICS Oil Odors: Leaky Oil Tank Piping OIL SAFETY VALVES OIL TANKS OIL TANK GAUGES OIL TANK LEAKS OIL TANK SLUDGE OIL TANK TESTING OIL TANKS, BURIED PLASTIC HEATER VENT RADIANT HEAT RADIANT HEAT Floor Mistakes to Avoid RADIANT SLAB FLOORING CHOICES RADIANT SLAB TUBING & FLUID CHOICES RADIATORS RELIEF VALVES - TP Valves on Boilers Relief Valves - Water Heaters SAFETY DURING HEATING INSPECTION Safety Recalls BLUERAY Recall CHIMNEYS & Flues - Asbestos Transite Goodman HTPV RECALL Heat Recovery Ventilator RECALL Lennox Furnace Manuals Lennox WARNING Weil McLain RECALL SAFETY DURING HEATING INSPECTION SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection STAIN DIAGNOSIS on Indoor Surfaces STEAM HEATING SYSTEMS Cad Cell Relay Switch Flame Sensors Low Water Cutoff Valves, Boilers Mixing Valves Relief Valves - TP Valves Sight Glass, Steam Boiler Pressure Switch, Steam Boiler Spill Switches Stack Relay Switch Steam Vents LOW WATER CUTOFF CONTROLS Water Feeder Valves, Steam TANKLESS COILS Mixing Valves Tankless Coil Leaks THERMAL EXPANSION of MATERIALS THERMAL MASS in BUILDINGS THERMAL MASS in UPSTAIRS THERMAL TRACKING & HEAT LOSS THERMOSTATS Transite Pipe Chimneys & Flues WATER HEATERS ZONE VALVES More Information  InspectAPedia ® Home & Site Map InspectAPedia Blog - News Updates Air Conditioning & Heat Pumps Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure Accuracy & Bias Pledge Contact Us |
Guide to Mixing Valves & Anti Scald Valves on Water Heating Equipment
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| Water Temperature Setting | Exposure Time | Effects of Exposure to Hot water at These Temperatures |
|---|---|---|
| Water at 100 degF or below | See safety note. | Most water heaters are unlikely to scald an adult occupant; |
| Water at 120 degF | 5 minutes | 2nd & 3rd degree burns on adult skin |
| Water at 130 degF | 30 seconds | 2nd & 3rd degree burns on adult skin |
| Water at 140 degF | 5 seconds | 2nd & 3rd degree burns on adult skin |
| Water at 150 degF | 1 1/2 seconds | 2nd & 3rd degree burns on adult skin |
| Water at 160 degF | 1/2 second | 2nd & 3rd degree burns on adult skin |
| Safety Note: Hot Water Scald Burn Warning for Infants, Children, Elderly: great care must be taken when exposing infants or children to warm or hot water as they can be badly burned quickly and at shorter exposure times. | ||
| Source: A.O. Smith | ||
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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). If your hot water temperatures are too low, see Temperature of Hot Water is Too Low If you do not have enough hot water pressure or hot water quantity, see HOT WATER IMPROVEMENTS |
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Anti-scald valves used with water heaters are also called tempering valves or mixing valves. An anti-scald valve mixes cold water in with the outgoing hot water to assure that hot water reaching a building fixture is at a temperature low enough to be safe.
In the sketch shown above, courtesy of Carson Dunlop, a tempering valve is shown installed at the hot water piping and tankless coil on a heating boiler. The drawing shows that hot water leaving the tankless coil has been heated to 180 degF. by the coil which is itself immersed in hot boiler water.
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.
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Our photo at left, taken at a heating boiler in Portland ME, shows a popular anti-scald valve made by the Watts Regulator Company. You can see that the black knob permits the user to set the outgoing hot water temperature leaving the valve, and if you look closely you can see the "HOT" and "COLD" and "MIX" indicators on the three ports of the body of the valve. Hot water enters the valve's right side, cold water enters the mixing valve's bottom, and mixed or tempered hot water leaves the valve at its left side. |
Why does an Anti-Scald Valve, mixing valve, or tempering valve on a tankless coil hot water system increases the total amount of hot water available?
The use of a mixing valve or anti-scald valve at a tankless coil permits us to set the Honeywell 6006 limit control switch or other boiler temperature or water heater temperature limit control to a higher number without having to worry about scalding occupants of the building.
Keeping the water at a higher temperature inside the heating boiler (with a tankless coil system) or in the water heater (with a separate domestic water heater or indirect-fired water heater system) means that there is more heat stored inside the heating boiler or water heater.
By adding cold water to the very hot water leaving the tankless coil or water heater, we draw hot water out of the water heater itself more slowly than we would without this addition.
Therefore we can expect to draw a larger quantity of (tempered) hot water from the tankless coil on such a system than otherwise. We will have more total domestic hot water for washing and bathing, and we have safer hot water (non-scalding) than if we omitted this pair of controls.
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Anti-scald valves are available built right into bathroom sink or shower fixtures, as you can see in our photo at left. These devices permit delivery of very hot water to a building area but protect occupants from scalding by mixing in cold water right at the sink, tub, or shower. As you can see on the control shown in our photo of a shower control in a shower-bath in Molde, Norway, fixture anti-scald valves may include a button and adjustment that lets the user demand hotter water than the control provides automatically. On this bath shower fixture the left-hand control turns water on or off, and the right-hand control permits adjustment of the water temperature. Turning the temperature control "down" or counter-clockwise increases water temperature but the control "snaps" into a locked position at a safe hot water temperature of about 100 degF. The user can obtain hotter water by depressing a red button and turning the control further. |
See HOT WATER IMPROVEMENT for 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.
Safety 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
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BOILERS, HEATING
BOILER OPERATION DETAILS
BOILER CONTROLS & SWITCHES
Air Bleeder Valves
Aquastat Functions
BOILER LEAKS CORROSION STAINS
BOILER OPERATING PROBLEMS
BOILER PARTS LIST
Boiler Pressure Controls & Settings
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Circulator Pumps & Relays
Draft Regulators, Dampers
Expansion Tanks
Gauges on Heating Equipment
Limit Switches, Boilers
Mixing Valves
Relief Valves - TP Valves
Reset Switch - Primary Control
Reset Switch - electric motors
Spill Switches
Stack Relay Switch
Thermostats
Water Feeder Valves, Hydronic Boiler
Zone Valves
WATER HEATERS
ZONE VALVES
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