Thermostatic mixing valves sit at the intersection of two competing demands in domestic hot water system design: storing and distributing water hot enough to suppress Legionella bacteria, while delivering water cool enough at fixtures to prevent scalding. For mechanical engineers, plumbing contractors, and facility managers working on hospitals, long term care facilities, schools, and commercial buildings, choosing the right thermostatic mixing valve standard \u2014 ASSE 1017 master mixing valves or ASSE 1070 point-of-use valves \u2014 directly affects patient safety, code compliance, and long term system performance.<\/p>\n\n\n\n
Hot water scalds remain a leading cause of preventable injury in healthcare and residential settings. The American Burn Association reports that water at 140\u00b0F can cause a third-degree burn in roughly five seconds, while at 120\u00b0F the same burn requires several minutes. Legionella pneumophila, the bacterium responsible for Legionnaires’ disease, thrives in stagnant warm water between 77\u00b0F and 108\u00b0F, making cooler distribution temperatures a Legionella amplification risk. The thermostatic mixing valve is the engineering control that resolves this tension.<\/p>\n\n\n\n
This guide explains the differences between ASSE 1017 and ASSE 1070 thermostatic mixing valves, when each applies, how Canadian and US codes treat them, and how to specify, size, and commission them on healthcare, institutional, and commercial projects.<\/p>\n\n\n\n
A thermostatic mixing valve, often abbreviated TMV, is a plumbing component that blends hot and cold water to deliver a controlled outlet temperature. Inside the valve body, a wax or liquid filled thermostatic element expands and contracts in response to outlet water temperature. As the element moves, it shifts a piston or shuttle that adjusts the relative openings of the hot and cold inlet ports.<\/p>\n\n\n\n
The result is a self regulating valve that maintains its setpoint within tight tolerances even as inlet pressures or temperatures vary. When cold water supply suddenly drops in pressure, as can happen when a toilet is flushed nearby, a properly designed TMV reduces hot water flow proportionally, preventing the scalding event that would otherwise occur.<\/p>\n\n\n\n
TMVs are categorized in North America by their ASSE (American Society of Sanitary Engineering) standard certifications. The two most relevant standards for building plumbing applications are ASSE 1017 and ASSE 1070, with additional standards such as ASSE 1016 covering shower and bath specific applications and ASSE 1071 covering tepid water for emergency safety equipment.<\/p>\n\n\n\n
ASSE 1017 covers master, or system, mixing valves installed near the source of domestic hot water. These valves blend stored hot water, typically held at 140\u00b0F or higher to control Legionella, down to a tempered distribution temperature, often in the range of 120\u00b0F to 130\u00b0F.<\/p>\n\n\n\n
A master mixing valve is installed downstream of the hot water heater or hot water storage tank, on the supply line that feeds the building domestic hot water distribution system. In larger buildings, multiple ASSE 1017 valves may be installed at the source of each riser or zone. The cold water inlet to the master mixing valve typically comes from the main domestic cold water supply, while the hot inlet comes from the storage tank or heater outlet.<\/p>\n\n\n\n
ASSE 1017 valves are not certified for direct connection to fixtures used by occupants. They lack the sub-second pressure compensation and cold water failure response required to prevent scalding under fixture conditions. The standard does not require the same fast acting failure behavior demanded by ASSE 1070. For these reasons, an ASSE 1017 valve cannot substitute for an ASSE 1070 valve at point of use, even if the master valve setpoint is below the typical scalding threshold.<\/p>\n\n\n\n
ASSE 1017 specifies temperature regulation tolerance, minimum operating flow rate, maximum flow rate, and pressure drop characteristics. The valve must hold its setpoint within defined bands across the rated flow range. Temperature accuracy under steady state conditions is typically within 3\u00b0F of setpoint when supply conditions are within published limits.<\/p>\n\n\n\n
Modern healthcare design often stores domestic hot water at 140\u00b0F or higher and uses ASSE 1017 master mixing valves to blend the distribution loop down to 122\u00b0F to 125\u00b0F. This range supports comfortable handwashing, reduces scald risk in areas not equipped with point of use valves, and limits the available range for downstream point of use TMVs to control. The remaining safety margin is provided by ASSE 1070 valves at the fixtures themselves.<\/p>\n\n\n\n
ASSE 1070 covers thermostatic mixing valves installed at or near individual fixtures to provide the final temperature limitation before water reaches the user. These are also called point-of-use, point-of-delivery, or anti-scald valves.<\/p>\n\n\n\n
ASSE 1070 valves are installed under lavatories, at hand washing stations, at specialty fixtures in healthcare, and at other points of personal hygiene use. The 1070 valve receives a tempered hot water supply from the building distribution loop and a cold water supply, then delivers a precisely regulated outlet temperature, typically between 95\u00b0F and 110\u00b0F depending on application.<\/p>\n\n\n\n
The defining feature of ASSE 1070 is the cold water failure response. If cold water supply pressure or flow drops, an ASSE 1070 valve must reduce or stop hot water flow within a specified time to prevent scalding. ASSE 1070 also requires tighter temperature regulation under varying inlet conditions, with outlet temperature held within a narrow band during specified pressure and temperature transients.<\/p>\n\n\n\n
The International Plumbing Code, the Uniform Plumbing Code, and the National Plumbing Code of Canada all require ASSE 1070 protection or equivalent at fixtures used for personal hygiene in many occupancies. Healthcare and long term care occupancies have particularly strict requirements. Provisions in the National Plumbing Code of Canada and similar provincial regulations require maximum delivery temperatures at fixtures used for personal hygiene, with healthcare specific limits often stricter than commercial limits.<\/p>\n\n\n\n
Typical ASSE 1070 setpoints are around 110\u00b0F for lavatory faucets in commercial buildings, 105\u00b0F or lower for public restrooms in schools and child care, and 100\u00b0F to 105\u00b0F for healthcare facilities serving vulnerable populations. Tepid water for safety showers and emergency eyewash, governed by ANSI Z358.1, falls in a 60\u00b0F to 100\u00b0F range and may require ASSE 1071 valves rather than ASSE 1070.<\/p>\n\n\n\n
The current best practice in healthcare and commercial domestic hot water design uses both ASSE 1017 and ASSE 1070 valves in series to manage the conflict between Legionella suppression and scald prevention.<\/p>\n\n\n\n
The first stage is the ASSE 1017 master mixing valve, which reduces stored hot water from 140\u00b0F or higher down to a distribution temperature near 122\u00b0F. This temperature is high enough to limit Legionella growth in the distribution piping while low enough to reduce scald severity if a fixture fails.<\/p>\n\n\n\n
The second stage is the ASSE 1070 point-of-use valve at the fixture, which reduces the 122\u00b0F distribution water down to 105\u00b0F or 110\u00b0F at the actual handwashing point. This valve handles fast pressure transients and cold water failure conditions that the master valve cannot.<\/p>\n\n\n\n
This layered approach is consistent with ASHRAE Standard 188 (Legionellosis: Risk Management for Building Water Systems) and ASHRAE Guideline 12, and is referenced in CDC guidance on water management programs in healthcare facilities. Canadian healthcare engineers should also reference CSA Z317.1 for special requirements in healthcare plumbing systems.<\/p>\n\n\n\n
Proper sizing is essential. Undersized valves cannot deliver design flow without excessive pressure drop, while oversized valves struggle to regulate at low flow conditions. Both extremes cause poor temperature control and user complaints.<\/p>\n\n\n\n
Size ASSE 1017 master mixing valves based on the peak demand flow of the served distribution system. Calculate peak demand using fixture unit methods from the applicable plumbing code, then check against the manufacturer published flow range. Master valves often have a stated minimum flow below which temperature regulation degrades; this minimum should be lower than the recirculation flow of the hot water loop if a circulator is used. Many large facilities install two or more master valves in parallel so that low flow conditions remain within at least one valve regulating range.<\/p>\n\n\n\n
Size ASSE 1070 valves based on the maximum simultaneous demand of the fixtures they serve. A single valve under a single lavatory is sized for a 1.5 to 2.2 gpm faucet. A valve serving a battery of four lavatories may need to handle 6 to 8 gpm peak. Verify that the valve minimum operating flow is below the lowest expected single fixture draw, especially when serving low flow lavatory aerators rated below 0.5 gpm.<\/p>\n\n\n\n
TMVs introduce pressure drop, typically 5 to 10 psi at design flow. Account for this in domestic water booster pump sizing, especially in high rise buildings where each zone may have an ASSE 1017 master valve at the floor level. Cumulative pressure losses from check valves, master mixing valves, point-of-use mixing valves, and fixture stops can easily exceed 25 psi between the booster pump discharge and the highest fixture in a tall building.<\/p>\n\n\n\n
Legionella risk management is now a mainstream component of healthcare and commercial building design. ASHRAE 188 requires water management programs for many building types, and the Centers for Medicare and Medicaid Services requires Legionella prevention programs at certified facilities in the United States. In Canada, public health agencies in Ontario, Quebec, and British Columbia have published Legionella guidance for healthcare and senior living facilities.<\/p>\n\n\n\n
Best practice stores domestic hot water at 140\u00b0F or higher and circulates the distribution loop to maintain a return temperature of at least 124\u00b0F at the inlet to the storage tank. Cooler return temperatures support biofilm formation and Legionella amplification. ASSE 1017 master valves located downstream of storage allow a hotter distribution loop while still protecting downstream piping from scald risk through the layered ASSE 1070 valves.<\/p>\n\n\n\n
Canadian Standards Association Z317.1 covers special requirements for plumbing in healthcare facilities. Provincial regulations in Ontario, British Columbia, Alberta, and Quebec build on the National Plumbing Code with healthcare specific provisions. Engineers working on hospital, long term care, and senior living projects in Canada should review the applicable provincial requirements and any health authority specific design guides early in design development.<\/p>\n\n\n\n
US healthcare engineers should reference the Facility Guidelines Institute Guidelines for Design and Construction of Hospitals, ASHRAE 188, and state level health department requirements. Veterans Affairs facilities and military medical facilities have additional water safety requirements that may exceed the baseline guidelines.<\/p>\n\n\n\n
A few patterns appear repeatedly in design and installation reviews:<\/p>\n\n\n\n
Specifying a single ASSE 1017 master valve at the temperature normally provided at fixtures and omitting point-of-use ASSE 1070 valves. This eliminates the layer of protection that prevents scalding under cold water failure and does not satisfy code at fixtures used for personal hygiene in many jurisdictions.<\/p>\n\n\n\n
Installing ASSE 1070 valves without isolation valves on both inlets. Field service requires the ability to isolate hot and cold inlets independently to verify valve function and replace internal cartridges or thermostatic elements.<\/p>\n\n\n\n
Failing to specify integral check valves or installing the TMV without external check valves. Cross flow between hot and cold supplies through a TMV creates code violations and uncontrolled mixed water in supposedly cold lines, which then becomes a Legionella amplification path.<\/p>\n\n\n\n
Sizing valves based on pipe size rather than flow rate. A TMV body is sized for flow, not for matching the connecting pipe diameter. Reducers and adapters are normal and necessary on properly sized TMV installations.<\/p>\n\n\n\n
Neglecting the recirculation strategy. Master valves serve their purpose only when the loop temperature is maintained. A failed circulator or undersized loop creates stagnation that the master valve cannot solve, and the resulting cool zones become Legionella amplification sites.<\/p>\n\n\n\n
Forgetting the minimum operating flow. Lavatory aerators with 0.5 gpm flow restrictors may cause point-of-use TMVs to fall below their regulated range, leading to temperature swings that frustrate users and can trigger scalding complaints.<\/p>\n\n\n\n
ValveAtlas supplies ASSE 1017 master mixing valves, ASSE 1070 point-of-use valves, and ASSE 1071 emergency tempering valves from leading manufacturers, with stock available across Canada and the United States. Our team supports engineers, contractors, and facility managers on:<\/p>\n\n\n\n
Selection of TMV models and setpoints suited to the project occupancy, code requirements, and Legionella management plan, including coordination with the facility water management program.<\/p>\n\n\n\n
Sizing reviews including verification of minimum and maximum flow ranges, pressure drop budgets, and recirculation compatibility with the planned hot water distribution strategy.<\/p>\n\n\n\n
Submittals and CAD details suitable for inclusion in mechanical drawings and shop drawings, with cut sheets showing pressure drop curves and temperature regulation data.<\/p>\n\n\n\n
CSA certification confirmation, CRN registration where required, and bilingual French and English documentation for Quebec projects.<\/p>\n\n\n\n
Field commissioning support including setpoint verification and witness testing for healthcare commissioning protocols where specified by the project.<\/p>\n\n\n\n
Whether the project is a new long term care facility in Manitoba, a hospital expansion in Ohio, a school district retrofit in Ontario, or a hotel renovation in Washington state, ValveAtlas can help select and supply the right thermostatic mixing valves for the application.<\/p>\n\n\n\n
The choice between ASSE 1017 and ASSE 1070 thermostatic mixing valves is not really a choice between competing options. The two standards cover different functions in a complete domestic hot water safety strategy: the master mixing valve manages distribution temperature for Legionella control and broad scald reduction, while the point-of-use valve provides the final pressure compensated, fast acting temperature limitation at the fixture.<\/p>\n\n\n\n
For healthcare facilities, schools, long term care residences, hotels, and other occupancies serving vulnerable populations or carrying elevated Legionella risk, both standards play essential roles. Master valves alone are not sufficient. Point-of-use valves alone leave Legionella risk in the distribution piping. Together, they provide the layered defense modern codes and standards expect.<\/p>\n\n\n\n
To discuss an upcoming healthcare, commercial, or institutional domestic hot water system, contact the ValveAtlas team. Our technical specialists can support specification, sizing, and supply for thermostatic mixing valves and supporting components across Canada and the United States.<\/p>","protected":false},"excerpt":{"rendered":"
Compare ASSE 1017 master and 1070 point-of-use thermostatic mixing valves. Healthcare design, scald prevention, and Legionella control best practices.<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"content-type":"","iawp_total_views":0,"footnotes":""},"categories":[175,21,23],"tags":[],"class_list":["post-43385","post","type-post","status-publish","format-standard","hentry","category-hydronic-hvac-engineering","category-industry","category-tips-tricks","category-175","category-21","category-23","description-off"],"acf":[],"_links":{"self":[{"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/posts\/43385","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/comments?post=43385"}],"version-history":[{"count":0,"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/posts\/43385\/revisions"}],"wp:attachment":[{"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/media?parent=43385"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/categories?post=43385"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/valve-atlas.com\/fr_ca\/wp-json\/wp\/v2\/tags?post=43385"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}