ASSE 1082, Performance Requirements for Water Heaters Used as Temperature Control Devices for Hot Water Distribution Systems

ASSE 1084, Performance Requirements for Water Heaters Used as Temperature Limiting Devices for Fittings

ASSE 1085, Performance Requirements for Water Heaters Used as Temperature Control Devices for Emergency Equipment

Standards are the final stopping point for innovation in our industry. For all the great new products that you see at trade shows, the ones that spawn a competitive space become the signal to create minimum performance requirements. Of those, a subset of the water heater market has been able to control their output temperature precisely enough such that there is no need for redundant downstream mixing valves. Current model code language in the Uniform Plumbing Code (UPC)® and International Plumbing Code (IPC)® assumes that the temperature output control for a water heater operates the same as it did 50 years ago. ASSE International will be releasing three new standards: ASSE 1082, Performance Requirements for Water Heaters Used as Temperature Control Devices for Hot Water Distribution Systems, ASSE 1084, Performance Requirements for Water Heaters Used as Temperature Limiting Devices for Fittings, and ASSE 1085, Performance Requirements for Water Heaters Used as Temperature Control Devices for Emergency Equipment, to create the equivalent performance and safety requirements of the ASSE 1017, Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems, ASSE 1070/ASME A112.1070/CSA B125.70, Performance Requirements for Water Temperature Limiting Devices, and ASSE 1071, Performance Requirements for Temperature Actuated Mixing Valves for Plumbed Emergency Equipment, respectively.

A Brief Background
The impetus to create these standards comes from the instantaneous (i.e. tankless, on-demand) water heater industry. These products are capable of controlling water temperature within the tolerances of the ASSE 1017 and 1071 standards, but the model codes require that the water heater not be the point of final control. At the same time, the products have heater control designs that compete with the control features of downstream mixing valves resulting in potentially inconsistent temperatures at point-of-use. To combat this, some manufacturers (both tank and tankless) have provided a bundled system with the appropriate temperature control/limiting valve for better performance. A more elegant solution for the benefit of the plumbing system is to avoid that workaround altogether – which is where these standards fit. ASSE 1082, 1084, and 1085, therefore, optimize plumbing designs by requiring the same levels of protection from thermal shock and scalding on the heaters themselves as the current mixing valve standards.

From the beginning of development, it was quickly observed at the working group that the best route would be to mimic the structure of the existing 1017, 1070, and 1071 standards. This is so the standards can be easily adopted and accepted by the model codes. Mirroring the scope of the existing standards and adding on the heater control performance requirements allows for an easy sell to authorities having jurisdiction and plumbing designers.

Those heater requirements themselves are already well documented in other safety standards, e.g. the ASME Boiler and Pressure Vessel Code, ANSI Z21.10.1 and .3, and many UL standards. The working group allowed for flexible product designs, as the goal was to be technology-neutral. While these safety standards are referenced in ASSE 1082, 1084, and 1085, they are actually non-mandatory as existing code requirements will drive this continually evolving need.


Temperature Performance
ASSE 1082, 1084, and 1085 make the assumption that the worst controls a heater will have will be at the maximum energy output at the maximum flow rate, and also at the minimum flow rate. This same assumption is in the ASSE 1017 and 1071 standards and is made explicit in these standards – the maximum flow rate drives the appropriate tolerance band. For both ASSE 1082 and 1085, those same tolerance bands are paralleled, and a new temperature control requirement had to be given for ASSE 1084 (for point of use) that parallels ASSE 1085 (for emergency fittings). While ASSE 1070 (for point of use) is written for temperature limiting, those requirements would not be sufficient for a product that adds energy into a system.

In order to translate the original tolerance bands to be appropriate for the heater, the standards begin by assuming a given temperature rise, accepting the manufacturer’s maximum power output rating, and then correlating that to a maximum flow rate and, therefore, temperature tolerance. That same tolerance is also checked at the lowest flow rate.

For example, a residential 199kBTU/hr (58.3kW) gas-fired heater can theoretically raise the water temperature by +70°F (+39 °C) when flowing at 9gpm (34.4 L/min). This results in an output tolerance requirement of ±5°F (±2.8 °C), per ASSE 1082.

For ASSE 1082, the tolerance bands are defined around a +70°F (+39 °C) rise, which are derived from DOE requirements.

For ASSE 1084, the tolerance band is defined around a +55°F (+30 °C) rise, which is derived from the 1070 standard where the temperature limit test is set at 105°F (40 °C) and the incoming cold water temperature is 50°F (10 °C).

For ASSE 1085, the tolerance bands are defined around a +35°F (+19.4 °C) rise since the target is 65-90°F (18.3-32.2 °C) as per ASSE 1071, as the intent is only to heat the water to a tepid temperature for emergency needs.

Intersections with other Standards & Regulations
There are numerous standards that address most, if not all, of the safety concerns associated with adding energy into a closed water system. These new standards are not intended to retest the products against those existing standards. It will be left to the discretion of the certifying body as to which safety standards are appropriate for the product in question. Enforcement by the AHJ will also be driving whether or not the product is installed. Annex A in each standard gives a list of potential, but non-mandatory, references to guide the reader.

There will be proposals associated with these standards covering two key aspects for the upcoming IPC code review cycle that starts in early January. Those proposals aim to have resolutions adopted that:

  1. These types of water heaters be allowed without downstream mixing valves to control water temperature;
  2. These products offer the same type of protection as the thermal shock and/or temperature limiting requirements of existing standards.

Within the IPC, expect language to be proposed for some of the following suggested locations:

For ASSE 1082
501.8 – Temperature controls [for hot water supply systems]
504.8 (new) – Water heaters having appropriate temperature control
607.1.1 – Temperature limiting means
613.2 (new) – Water heaters having appropriate temperature control

For ASSE 1084
408.3 – Bidet water temperature
416.5 – Tempered water for public hand-washing facilities
424.5 – Bathtub and whirlpool bathtub valves
607.1.2 – Tempered water temperature control

For ASSE 1085
411.3 (new) – Temperature output

Where the Standards Are Silent
Trade-offs occur all the time in product and standard development. In this case, making requirements around Legionella were specifically not included within the scope of the standard. The working group agreed that there is a significantly diverse set of stances in the market such that adding any elevated requirements would not be in the spirit of minimum performance requirements for temperature control. Still, manufacturers are free to utilize the standards for their advertised temperature ranges in order to demonstrate that their products combat bacterial growth in water heating systems. For those that are interested, refer to ASHRAE 188, Legionellosis: Risk Management for Building Water Systems, ( and to the Center for Disease Control website for their toolkit (

What is great about this water heater working group is that we have a healthy cross-section of tank-type heater, tankless heater, and valve manufacturer representation to come to consensus on these critical standards. It is ASSE International’s sincere hope that this will appropriately advance our industry for better plumbing system designs, and help drive product innovation that will become commonplace in future revisions.


  1. “Instantaneous” meaning having <2 gallons of rated storage volume for consumer electric and gas-fired water heaters per 10 CFR 430.32(d). For commercial gas-fired, this means >200kBTU/hr and ≥4kBTU/hr per gallon of stored water per 10 CFR 431.102.
  2. 10 CFR 431, Subpart G, Appendix A for commercial water heaters states a +70°F (+39 °C) rise, and 10 CFR 430, Subpart B, Appendix E for residential water heaters states a +67°F (+19.4 °C) rise.