manual hot water mixing valve 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.

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Guide to Using a Manual Hot Water Tempering Valve on the Domestic Hot Water Supply

Manual mixing valve (C) Daniel Friedman

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Article Contents

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.

manual hot water mixing valve

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,

  1. 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.
  2. 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.

Anti-Scald & Hot Water Safety Articles


Continue reading at POINT of USE BUILT-IN FIXTURE ANTI-SCALD VALVES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



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 QUANTITY IMPROVEMENT

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