Heat-Timer® Corporation

What “Penny Wise & Pound Foolish” says about Domestic Hot Water Solutions

The actual phrase “penny wise, and pound foolish” is often mistakenly credited to Benjamin Franklin, but it actually originated with an Oxford Scholar named Robert Burton in his book, “The Anatomy of Melancholy” written in 1621!

Needless to say, in 1621 domestic hot water wasn’t even a thing. It was before the advent of electricity, multi-story distributed hot water systems, and certainly before the advent of modern boilers, computerized boiler controls and mixing valves.

And yet the phrase is nowhere more relevant than when it is applied to DHW installations where mixing valves are sometimes omitted for small overall reductions in material cost or piping complexity in a commercial, domestic hot water setting.

So here’s “penny wise and pound foolish” as applied to your domestic hot water system.

The Purpose of a 3 Way Mixing Valve in DHW

In DHW applications using traditional direct-fired storage tank systems, a mixing valve has always been an important part of the overall system design as shown in the graphic below:

The typical 3-way valve serves several primary purposes:

  1. It allows hot water storage tanks to be maintained at temperatures high enough to sterilize the water supply (~140F – 160F per OSHA guidelines) and kill bacteria like Legionella and more.
  2. It “mixes” hot water from the tank with part of the cold water supply to insure that no one burns their hands from the hot water supply when it comes out of your sink or shower. (~110 F)
  3. It provides fail-safe operation and can provide alarms for systems in the event of an unexpected failure with the DHW system.

According to the Centers for Disease Control & Prevention (CDC), incidents of Legionnaire’s disease have been on the rise for over a decade.


These numbers are just what is reported of course. The National Academies of Sciences, Engineering, and Medicine estimates that as many as 70,000 people may suffer from the disease each year, according to a report released in August 2019. The disease can cause severe sickness and even death. Individuals with a history of health issues, smoking or who are over 50 are even more at risk. For facilities, the consequences of finding the bacteria can be catastrophic, even if not deadly. The water must be shut off, expensive mitigation strategies can be required, there is almost always negative media coverage often national, and of course, there is the potential for lawsuits or even financial ruin.

How Saving Pennies threatens the whole system.

It turns out that there is a lot of misinformation out there about what does and doesn’t compromise the integrity of a domestic hot water delivery system. Some of this misinformation is even propagated by manufacturers of tankless system who want you to believe that their on-demand systems are safe to run at much lower temperatures, thus saving energy.

The truth is however quite simple and the science behind it is easily available on the websites of Federal regulatory agencies like the CDC, the World Health Organization, and private research companies.

Consider the following commonly used table of Legionella growth.

The disinfection of your hot water is dependent on two primary things:  The temperature of the hot water and the time it remains at that temperature.  Period. And the only way to manage the proper disinfection of hot water, without risking scalding injuries at the fixture, is through management of water temperatures using a 3 way mixing valve.

A Little More Work, A Lot More Safety

Heat-Timer® recognized a while ago that installers needed a simpler and faster solution to the installation of 3 way mixing valves. That’s why we developed the Electronic Tempering Valve (ETV) and the Electronic Tempering Station or ETS. The ETS provides installers the convenience of a pre-piped and pre-wired assembly of the ETV valve and module. The installers only need to connect the hot and cold water supply, and provide power to the controller to have a completely safe, pre-plumbed solution to domestic hot water safety.

For more information on Heat-Timer’s electronic tempering valve solutions for domestic hot water applications, please contact a Heat-Timer® representative today at: (973) 575 4004.