Manually-Operated Temperature Mixing Valves & Anti Scald Valves
MANUAL ANTI-SCALD TEMPERING VALVES - CONTENTS: What are manual hot water temperature mixing valves - anti-scald valves, or temperature compensation valves on heating boilers, tankless coils, & water heaters. Where do we locate the manual mixing valve and how should it be set to provide good hot water temperature without risking a scalding burn?
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Manually-operated anti-Scald valves used at heating boilers or at stand-alone hot water cylinders, geysers, or water heaters:
This article describes a simple manually-operated control that is set to mix cold in with outgoing hot water to avoid risking a scalding burn for building occupants who use hot water. We warn that depending on the hot water source (a water geyser or hot water cylinder or hot water heater versus a tankless coil at a heating boiler) you may need to adjust this valve at the start and end of the heating season to avoid hot water burns.
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.
By manual hot water tempering valve we mean that the plumber has installed an ordinary plumbing valve and a cold water bypass pipe to mix some cold water into the water heater's outgoing hot water supply. This valve must be adjusted by the building occupant to obtain the desired temperature.
Our photo 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.
Watch out: a manual-only mixing valve is inherently an unsafe or unreliable means of scald burn protection. Water temperatures produced by the water heater may change for a variety of reasons surprising and even burning building occupants.
Which Way to Turn a Manual Anti-Scald Valve or non-Automatic Mixing Valve to Control Hot Water Temperature
By "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.
Here is a manual mixing valve on a hydronic heating system.
You may find a ball-valve like this controlling domestic hot water temperature, radiant floor heating temperature, or even individual heating zone water temperature.
This manually controlled valve (a human has to turn it) feeds some cold water into the hot water that is piped to building plumbing fixtures.
So, for a manually operated tempering or mixing valve,
Opening (turning counter-clockwise) a manual mixing valve mixes in more cold water and makes the resulting "hot water" in the building cooler - it lowers the temperature of the outgoing hot water.
Closing (turning clockwise, or "in" or "down" or "closed") a manual mixing valve mixes in less cold water so it makes the resulting "hot water" in the building hotter - it raises the hot water temperature.
When Should We Adjust a Manual Hot Water Tempering or Mixing Valve?
Hot Water Made by a Tankless Coil & Heating Boiler - Manual Adjustment of Tempering Valve
Watch out: if your hot water system uses a manual tempering valve and your hot water is made by a tankless coil and a hot water or steam heating boiler (as opposed to a separate hot water heater and tank), you will want to manually adjust the valve to produce a safe (below scalding temperature) hot water temperature measured at the plumbing fixture located closest to the hot water source (the heating boiler).
During the heating season when the boiler is hotter, you'll want to adjust the valve again to prevent the hot water temperature from being too high. In sum, you'll need to change the manual mixing valve setting twice a year.
At the end of the heating season, when the same heating boiler continues its job of making domestic hot water at a tankless coil or side-arm coil, you will need to adjust the manual tempering valve again to close off some of the mixed-in cold so that your water temperature is hot enough. That's because on most heating boilers using an aquastat or even separate individual boiler temperature controls, the boiler remains at a lower temperature when the building thermostats are never calling for heat.
Hot Water Made by a Separate Water Heater Using a Manually-Adjusted Tempering Valve
A second reason you may need to adjust the manual hot water mixing valve is that in some areas the temperature of the cold water entering the building may vary by season.
Even if your hot water is made by a separate hot water heating tank, your system might have a manual mixing valve installed and you might need to adjust that setting seasonally as incoming water temperatures change.
More information about tankless coils, how they work, what goes wrong, and their controls, is at TANKLESS COILS.
See WATER PIPE CLOG REPAIR for a discussion of loss of water pressure due to clogged piping or clogged tankless coils.
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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:
 "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.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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