Mixing Valves & Anti Scald Valves on a Tankless Coil How to install & set hot water temperature at a tankless coil
ANTI SCALD VALVE at TANKLESS COIL - CONTENTS: how is the hot water temperature controlled at a tankless coil on a boiler: automatic anti-scald valves or automatic compensation valves on heating boilers & at tankless coils: location, use, control, setting, safety.
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Anti-Scald protection at the tankless coil hot water system on a boiler:
This article explains how to install or locate the hot water temperature control at a tankless coil hot water system on a heating boiler. We describe what the tankless coil temperature control looks like, how it works, and how to set the output hot water temperature to avoid scalding burns. This article includes the hot water temperatures you can expect when using this type of mixing valve or anti-scald valve at a boiler.
In this article series 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.
Guide to Installing & Setting Tankless Coil Hot Water Mixing Valves
Above, a Sparco Aquamix AM 100C automatic tempering valve or anti-scald valve. At page top, a Watts automatic anti-scald valve installed at a home heating boiler tankless coil used to provide domestic hot water.
Automatic Anti-Scald Tempering or Mixing Valves at a Tankless Coil - Water Pressure Balancing Type
The Watts anti-scald valve shown above or the Sparco anti-scald valve shown earlier (or an equivalent product) is normally installed at a heating boiler tankless coil outlet or at the outlet of a stand-alone water heater.
This mixing or anti-scald valve contains an internal temperature sensor which permits the valve to add cold water to the outgoing hot water in order to limit the temperature of the hot water leaving the valve.
Our photo at left, taken at a heating boiler in Portland ME, shows a popular Watts™ 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.
Turning this Watts Reg. Co. automatic mixing valve clockwise makes the outgoing water temperature cooler. Turning the Watts mixing valve counterclockwise makes the outgoing water temperature hotter.
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.
Which 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:
I'm not sure which way to turn my hot water mixing valve. When you turn "down" on valve does it send less cold water or more. I believe it's less. Let me know. - U.S.A.
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.
Tankless Coil Hot Water Mixing Valve Output Temperatures
Using the modern Watts Regulator Co. Series LF1170 / LFL1170 Hot Water Temperature Control Valve instructions as an example, these valves control water temperature in the following ranges:
Table of Hot Water Mixing Valve Output Temperatures [Watts Series LF1170 & LFL1170]
Hot Water Mixing Valve Model
Cold Inlet Temperature
Hot Inlet Temperature
Factory Preset Outlet Temperature
Output Temperature Adjustment Range
Water supply pressure
60-70 °F (16-21 °C )
120 °F (49 °C)
90-160 °F (32-71 °C)
45 psi (3.15 bar)
Watts LFL 1170-M2
90 °F (31 °C)
60-120 °F (16-49 °C)
These mixing valves require a minimum supply pressure of 30 psi (207 kPa), and function with hot inlet water temperatures ranging from 120 to 200 °F (49-93 °C ), and with cold inlet temperatures from 40-85 °F(4-2 °C ).
Valve outlet temperature accuracy is +/- 3°F (1.7 °C ). There are other restrictions including a requirement that the difference between hot water and cold water pressures at the valve must not vary by more than 25%. The maximum tolerated pressure is 150 psi (10.3 bar). Lower pressure restrictions may apply when using CPVC or PEX piping & end connections.
Source: "Instructions Series LF1170 and LFL1170 Hot Water Temperature Control Valves", Watts Regulator Co. (2013)
Tankless Coil Anti-Scald Valve Safety Warnings
Watch out: read the installation instructions from the manufacturer of the product you are installing, both to make sure it's installed properly and thus will work as expected, and also so that you understand what to expect by way of hot water temperature control the product handles.
WARNING: Thermostatic mixing valves are intended to increase the supply of hot water available from the coil. They are not intended to prevent a scald hazard.
Similarly, the Watts Regulator Company's instructions for the installation of the Series LF1170 & LFL 1170 Hot Water Temperature Control Valves includes this warning: [Bold font is our emphasis]
WARNING: FAILURE TO COMPLY WITH PROPER INSTALLATION AND
MAINTENANCE INSTRUCTIONS COULD CONTRIBUTE TO THE VALVE
This Hot Water Master Tempering Valves cannot be used for tempering water temperature at fixtures. Severe bodily injury (i.e., scalding
or chilling) and/or death may result depending upon system water
pressure changes and/or supply water temperature changes. ASSE
standard 1016, 1069 or 1070 listed devices should be used at fixtures to prevent possible injury.
These Hot Water Tempering Valves are designed to be installed at or near
the boiler or water heater. They are not designed to compensate for system pressure fluctuations and should not be used where ASSE standard
1016, 1069 or 1070 devices are required. These valves should never be
used to provide “anti-scald” or “anti-chill” service.
The components of the system must be of materials with a construction
capable of withstanding the high limit output temperatures of the water
heating source. - Watts (2013)
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"Instructions Series LF1170 and LFL1170 Hot Water Temperature Control Valves", Watts Regulator Co. (2013), USA Tel: (978) 688-1811, Fax: (978) 794-1848,
Website: www.watts.com, Canada: Tel: (905) 332-4090, Fax: (905) 332-7068, Website: www.watts.ca
"BDS Series Oil-Fired Hot Water Boilers, Installation Instructions, Models GS-080 -> Crown BDS-236", Crown Boiler Company, BDS 12-99, Crown Boiler Co.
P.O. Box 14818
3633 I Street
Philadelphia, PA 19134
Website: http://www.crownboiler.com, retrieved 2/26/2014, original source: http://www.crownboiler.com/manuals/content/ All_Models/BDS%20Series%20%28all%20models%29.pdf
The following link provides access to literature or manuals for previous Crown products:
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 "Water Saving Tips: For Residential Water Use, Indoors and Out", Alliance for Water Efficiency, 300 W Adams Street, Suite 601 Chicago, Illinois 60606, Tel: 773-360-5100, 866-730-A4WE, Email: email@example.com, web search 12/14/11, original source: plumbingefficiencyresearchcoalition.org/
 "Danger in the Shower: 2008 Forum Looks at Hot Water", John Koeller, Home Energy, Jan/Feb 2009, Home Energy Magazine, 1250 Addison Street Suite 211B, Berkeley, Ca. 94702, Tel: (510) 524-5405 Email: firstname.lastname@example.org
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
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