It wasn’t too long ago that ASSE 1070 was touted as the standard which would solve all the problems with thermostatic mixing valves. Unlike an ASSE 1017 thermostatic mixing valve, ASSE 1070 valves would provide thermostatic mixing with failsafe (endpoint) protection.
In other words, if the valve failed to properly perform in setting the temperature, the water flow through the valve would close to a trickle. Thus, scalding would be prevented.
When the standard was first issued in 2004, it was immediately accepted by the plumbing code for all sorts of thermal-shock and anti-scald protection. It was considered such a good standard that ASSE 1016/ASME A112.1016/CSA B125.16 was revised to only apply to shower valves. No longer could a standalone tub filler or a lavatory faucet be evaluated to ASSE 1016/ASME A112.1016/CSA B125.16.
ASSE 1016/ASME A112.1016/CSA B125.16 was considered inferior to ASSE 1070 by some because the standard allowed balanced pressure protection. ASSE 1070 required thermostatic mixing protection. The level of protection can be considered significant if the water temperature is constantly changing.
The anti-scald advocates ballyhooed ASSE 1070 and went on the rampage in adding requirements throughout the plumbing code to require this level of protection in areas never considered to need anti-scald protection. One such application has been to public lavatory faucets. Prior to the development of ASSE 1070, public lavatories were required to be supplied with hot water having a maximum temperature. That was being accomplished by faucets listed to ASSE 1016/ASME A112.1016/CSA B125.16, or with a central thermostatic mixing valve complying with ASSE 1017.
Again, there has never been a scald issue with public lavatories. The temperature limitation was based on comfort. But, the advocates prevailed by having the plumbing codes require ASSE 1070 protection for public lavatories.
In 2015, ASSE 1070 was tri-harmonized with ASME and CSA. The new standard is identified as ASSE 1070/ASME A112.1070/CSA B125.70. The harmonization process results in ASSE giving up full control of the standard. The new edition also was coordinated with prior CSA requirements. The tri-harmonized standard is no longer a thermostatic mixing valve standard. There are no requirements for the device to be thermostatic mixing.
As a result of these major changes, an ASSE 1070/ASME A112.1070/CSA B125.70 device can no longer be compared to an ASSE 1017 thermostatic mixing valve. The scope of the standard states it regulates water-temperature-limiting devices, not thermostatic mixing valves. The scope further states it provides no protection against thermal shock.
What started as a thermostatic mixing valve no longer provides thermostatic mixing. All an ASSE 1070/ASME A112.1070/CSA B125.70 device does is limit the maximum temperature. Big deal!
We already had maximum temperature-limiting devices long before ASSE 1070 was developed as a standard. Those devices are called temperature-actuated flow-reduction devices or TAFRs. Like the tri-harmonized ASSE 1070/ASME A112.1070/CSA B125.70, TAFRs, regulated by ASSE 1062, cut off the flow of water before it reaches 120° F.
From the perspective of the specifying engineer, why specify an expensive ASSE 1070 device when you can specify an inexpensive ASSE 1062 TAFR? You receive the same level of scald protection. TAFRs typically are built into a showerhead, tub filler or aerator.
This major change also has confused many of the anti-scald advocates who supported ASSE 1070. Many believe an ASSE 1070 device still provides thermostatic mixing. To add further confusion, many manufacturers still produce a thermostatic mixing valve and identify it as complying with ASSE 1070. However, there are no requirements in the standard to verify that the device performs thermostatic mixing.
Changes to the status quo
Now there are proposals to further water down ASSE 1070/ASME A112.1070/CSA B125.70, allowing it to regulate upper temperatures less than 120°. If that goes through, forget about considering the device as an anti-scald device. It will merely become an upper temperature device.
A new standard being issued is ASSE 1084. This standard will regulate water heaters with the requirements comparable to ASSE 1070/ASME A112.1070/CSA B125.70. However, unlike ASSE 1070/ASME A112.1070/CSA B125.70, ASSE 1085 has performance requirements for temperature maintenance on the outlet of the water heater. Thus, in reality, an ASSE 1084 water heater will provide the same level of performance as an ASSE 1017 thermostatic mixing valve and an ASSE 1070/ASME A112.1070/CSA B125.70 temperature-limiting device. You get two valves for the price of one water heater.
Some consider these high-end water heaters to be point-of-use water heaters. However, there is no requirement for them to be point of use. You could install the water heater as a centralized water heater.
From an engineering perspective, if you want to provide thermostatic mixing with something other than a high-end water heater, you are back to only specifying an ASSE 1017 valve. For showers, you would specify a Type T ASSE 1016/ASME A112.1016/CSA B125.16 compensating shower valve. This is what we call a thermostatic-mixing shower valve. The other two types are Type P for pressure balancing and Type P/T for both pressure balancing and thermostatic mixing.
Perhaps it is time to change ASSE 1016/ASME A112.1016/CSA B125.16 to revert back to allowing fixtures other than shower valves to be regulated. ASSE 1016/ASME A112.1016/CSA B125.16 could require faucets and fixture fittings, other than shower valves, to only be Type T or Type P/T. This would eliminate the possibility of allowing pressure balancing as a means of providing anti-scald protection in any fixture other than shower valves. It also would be an appropriate standard for regulating faucets and fixture fittings for tubs, lavatories, bidets, sinks and similar fixtures.
Such a change also would reinstitute a standard to regulate thermostatic mixing valves with fail-safe protection. But this would result in the further demise of ASSE 1070/ASME A112.1070/CSA B125.70. It may be time for ASSE 1062 to become the standard regulating temperature-limiting devices. If this happens, ASSE 1070/ASME A112.1070/CSA B125.70 will fade into the sunset and become a meaningless standard.