How Low Can You (Really) Go?

To maximize master tempering valve selection, engineers need to understand minimum flow.

In the world of a plumbing systems design engineer, few tasks are as critical as properly selecting the thermostatic valve(s) that will temper water throughout a new facility. An engineer must consider many important factors when choosing large tempering valves or systems, commonly known as master mixers or Hi/Los.

At a bare minimum, all master tempering valves must be seal board- approved to ASSE 1017. Without this guarantee of performance, bather safety is put at risk. Beyond seal board approval, an engineer then considers maximum flow (at a given pressure drop), to assure a facility's tempered water requirements are met, and next minimum flow, to insure safe bathing during low demand periods (as few as one or two fixtures).

Other considerations include: the type of actuation technology employed to ensure optimal response time, the materials used to guarantee long life under adverse water conditions, and the built-in safety features that prevent unauthorized tampering.

However, the most critical performance criterion is temperature control across a broad range of flows and conditions, specifically at a manufacturers stated "minimum flow."

ASSE Emphasizes Minimum Flow

What do the new and revised standards say about minimum flow?

In the last two years, ASSE had revised its two major tempering valve standards (1016 and 1017) and added two more (1060 and 1070). New and some existing applications have driven new standard development. ASSE 1016 was becoming a certification catchall for more than it was originally intended. Because of the safety implications involved, the new and revised standards place a stronger emphasis on minimum flow testing.

ASSE 1016-1996, -2005
ASSE 1016-1996 is a bath and shower standard that has been historically adopted by other devices, such as those that control water to lavatories. Because showerheads are regulated to 2.5 gpm, the lowest flow required to pass ASSE 1016 is 2.5 gpm. More specifically, a compliant valve must hold +3 degrees F when subjected to pressure (types T/P, T, and P) and temperature changes (types T/P and T).

If flow is below 2.5 gpm, performance relies on the manufacturer's word or implication the valve(s) hold +3 degrees F when subjected to temperature and pressure changes. Just because a valve is ASSE-listed or compliant and states a minimum flow below 2.5 gpm, don't assume it meets the temperature control criteria of the standard. The key question to ask the manufacturer is how their valve performs (+3, +5, +10, +20F, +??) when tested according to 1016 at 0.5 gpm or 1.0 gpm. They should state this in writing and back up with test data.

This is particularly critical for lavatory tempering applications with single or multiple low-flow outlets. Lavatories in public restrooms and schools are often outfitted with 0.5 gpm aerators. Remember, an ASSE 1016-listed valve only ensures temperature control to 2.5 gpm. Anything less can result in dramatic changes to outlet temperature when pressure or temperature disturbances occur. ASSE 1016-2005 is now strictly a shower and bath/shower standard. ASSE 1070 was developed for lavatory applications and includes a manufacturer's "stated minimum flow"

Questions to Ask

So, when reviewing manufacturer's stated minimum flow, ask the following questions:

What does the minimum flow value represent in terms of performance to the standard?
Does the manufacturer specifically state the minimum flow performance relative to the standard, i.e., "minimum flow to ASSE 1017"

ASSE Standard 1016
Revision 1996:
Revision 2005:
ASSE Standard 1017
Revision 1994:
Revision 2003:
ASSE Standard 1069
Revision 2005:
ASSE Standard 1070
Revision 2004:
ASSE Standard 1071
Revision: Draft