At the recent ASPE Convention and Expo, I visited friends at the Leonard booth. I was invited to see their new electronic thermostatic mixing valves. Simply stated, it was cool. The adjustment of the hot water temperature setting was quick and easy on the basic model. The other models can connect to the building management system, or even your cell phone.

Electronic thermostatic mixing valves are not new. I remember many years ago being introduced to Armstrong’s Brain. That is also cool. Other manufacturers with electronic thermostatic mixing valves include: Watts Powers, Caleffi and Holby, to name just a few. It is anticipated that every thermostatic mixing valve manufacturer will have an electronic valve on the market in the near future.  

In many ways, this was prompted by a change in the standard ASSE 1017. There was a request to develop a new standard for electronic mixing valves that is similar to mechanical thermostatic mixing valves complying with ASSE 1017. That request was rejected, with the compromise being to modify ASSE 1017 to properly regulate all types of thermostatic mixing valves, including electronic valves.

The new standard was completed months ago; however, due to quirks in the consensus process, it was only officially approved and finalized this month. But every thermostatic mixing valve manufacturer was aware of the changes because of their involvement in the working group. Thus, the influx of new electronic mixing valves. 

When the updated standard was being developed, one of the questions that arose was whether there would be different temperature variations required between mechanical and electronic valves. Some of the electronic valve manufacturers were interested in tighter requirements for electronic valves. The claim being made was that electronic valves could hold a tighter tolerance, hence, they should be held to a higher level than mechanical valves.  

Others on the working group saw the attempt at tighter tolerances as a marketing gimmick to promote electronic valves over mechanical valves. The end result is the tolerance remains unchanged, whether mechanical or electronic. For lower flow rates, the hot water temperature can vary up to 3° F. For valves having a flow rate over 40 gpm, the variation in temperature can be 7° F. Between 5 and 40 gpm, the variation is 5° F.

Another hot issue during the updating of ASSE 1017 regarded mandating integral check valves. There were some who wanted all thermostatic mixing valves to have integral check valves. Not all manufacturers have integral check valves. There was also a question regarding the quality of some integral check valves.

The change in the standard requires valves with integral check valves to pass a new crossflow test, thus verifying the performance of the check valves. If integral check valves are not included in the thermostatic mixing valve, the manufacturer’s installation instructions must include a statement that check valves are required on the hot and cold water supply to the thermostatic mixing valve. 

What is not addressed in the updated standard is the issue of “creep” when there is a recirculation system. “Creep,” or unintended rise or lowering of the hot water temperature, is considered a design and installation issue, not a valve issue. This happens to be correct in that a proper by-pass has to be installed allowing some of the recirculating water to return to the water heater to reheat the water through the thermostatic mixing valve.

The bypass piping arrangement is typically addressed in the installation instructions for the thermostatic mixing valve. However, there is no requirement in ASSE 1017 for the manufacturer to include such installation instructions. Many manufacturers show a ball valve rather than a controlling or throttling valve on the bypass. The ball valve is often shown because of a misunderstanding of the plumbing code requirements. The plumbing codes allow a globe valve for controlling the water flow through a bypass. If the contractor does not properly set the bypass valve, there will be temperature creep through a manual thermostatic mixing valve.

I have noticed that some of the manufacturers of electronic mixing valves are promoting the fact that the electronic mixing valve will prevent creep and the setting of a bypass valve is unnecessary. That is one of the often missed advantages of an electronic mixing valve. During a no-flow, recirculation period of use, the electronic mixing valve will determine how much hot water to add through the bypass in order to maintain the hot water temperature at the set point. The electronics take the contractor setting out of the equation. I suspect all manufacturers will start to promote this benefit as another reason to consider switching to electronic mixing valves.

With the new edition of ASSE 1017, engineers will now be able to level the playing field between electronic mixing valves and mechanical thermostatic mixing valves. Every valve, whether electronic or mechanical, will have to meet the same requirements. As in the past, manufacturers will promote how much better their valves are compared to what the standard allows. That’s fine, just realize there are no testing requirements for “better” in the standard. However, a manufacturer can choose to share their test results from a third-party testing laboratory to prove their point.

Having been a member of the ASSE 1017 working group, just about every manufacturer asks us engineers whether there will be a switch to electronic mixing valves. My answer is always the same. It appears that the market for electronic mixing valves will only continue to grow. However, the market for mechanical thermostatic mixing valves, whether using liquid, wax, or bimetal, will always be a part of our profession. Engineers like being able to closely control the temperature of hot water.

The updated standard is a nice gift for the end of the year. I hope you can take time to spend with your family and friends during the holiday season. As we appear to be coming out of the great COVID-19 pandemic, I hope everyone has the opportunity to meet in person to celebrate the holidays.

I want to wish all of you a very Merry Christmas, Happy Hanukkah, Happy Holidays and a successful and Happy New Year. 

The views expressed here are strictly those of the author and do not necessarily represent PM Engineer or BNP Media.