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Quick answer from a licensed plumber: A thermostatic mixing valve blends hot and cold water to control the temperature of the mixed outlet. Choose it by location: ASSE 1017 for hot-water distribution, ASSE 1070 for fixture temperature limiting, and ASSE 1016 for an individual shower valve. A heater-outlet valve does not replace required protection at the fixture. Match the connection, flow and inlet temperatures before buying; the two options below serve different jobs.
Buying for a heater or a sink? Jump to the 3/4-inch FNPT HG110-D 25523 fit checks or the 3/8-inch compression HG145 24524 fit checks before choosing.
At a Glance
| Control | Water heater thermostat | Thermostatic mixing valve |
|---|---|---|
| What it sets | Tank storage temperature | Delivered water temperature |
| Reacts to pressure/temp swings | No | Within the selected valve’s specified inlet and flow conditions |
| Temperature protection | Sets storage; does not compensate at a fixture | Depends on listing, placement, commissioning and maintenance |
| Relevant standard | — | ASSE 1017 (distribution) · ASSE 1070 (fixture limiting) · ASSE 1016 (individual shower) |
The problem: storage and delivery are different temperatures
A hotter tank can provide more usable mixed water, but it also increases burn risk. The CPSC recommends 120°F for residential heaters to reduce scald risk; even 120°F water can burn with prolonged exposure. Do not treat a code maximum or a valve’s factory setting as a guarantee against burns.
CDC’s home-water guidance discusses 130–140°F storage for controlling germs alongside the increased burn risk, and recommends tap thermostatic valves above 120°F. It also advises discussing individual Legionella risk and a higher setting with a healthcare provider. A mixing valve does not disinfect water or make a higher setting right for every home.
What the valve actually does
A TMV sits on the hot line (typically right at the water heater’s outlet for a whole-house install, or under a fixture for point-of-use) with three connections: hot in, cold in, mixed out. Inside, a thermostatic element expands and contracts with the outlet temperature and continuously repositions a shuttle, throttling hot against cold to hold the set point.
Watts distinguishes source-of-supply valves from fixture protection and directs readers to the selected model’s inlet-temperature limits. The valve needs adequate hot and cold supplies and the specified flow to regulate properly.
If you are planning a water heater replacement, have the installer assess the storage setting, distribution layout and required fixture controls together. Adding one valve at the tank is not a substitute for commissioning the whole system.
What the code actually requires — and the standard mix-up to avoid
The 2024 International Plumbing Code, sections 412.3 and 412.5, limits individual shower/tub-shower and bathtub/whirlpool delivery to 120°F, with field adjustment following the maker’s instructions. Section 412.5 permits an ASSE 1070 temperature-limiting device or an ASSE 1082/1084 water heater, with a combination tub/shower exception. Section 412.3 requires a compliant point-of-use shower valve and does not allow an in-line thermostatic valve as its substitute. These are model-code provisions; check the locally adopted edition and amendments.
- ASSE 1017: controls the distribution temperature near the hot-water source. This listing alone does not provide adequate scald or thermal-shock protection at fixtures.
- ASSE 1070: limits temperature supplied to fixtures such as sinks and bathtubs. It provides scald protection within its application, not thermal-shock protection.
- ASSE 1016: applies to individual shower and tub/shower compensating valves. Our shower system guide covers those valve-and-trim choices.
Multiple listings do not mean multiple jobs at once. ASSE’s guidance says a valve installed as the distribution control cannot simultaneously satisfy required fixture protection just because its label also lists ASSE 1070. Placement and application matter.
Georgia’s DCA lists the 2024 IPC with Georgia amendments as its current plumbing code. Check the state’s current adoption and amendments and your local authority before permitted work.
Mixing valves, code limits and the parts that actually meet them — I write these as topics come up. Leave your email for the occasional note. No spam, no course funnel.
Whole-house vs point-of-use
- At the heater: a distribution valve blends water before it enters the hot-water distribution piping. Size it for the system’s demand and lowest operating flow; retain the required controls at sinks, tubs and showers. Keep isolation and service access available. During a heater swap, also check the transition fittings.
- Under a sink: a point-of-use valve limits the supply to that fixture. The HG145 below is an individual-faucet option, not a whole-house substitute. Leave room to inspect and service it. If you also use a recirculating pump, have the installer check the valve’s approved piping arrangement.
The honest failure modes
A changed outlet temperature is a reason to check the system, not proof that one particular part has failed.
- Blocked strainers or fouled checks: Cash Acme’s troubleshooting and service documents identify debris as a cause of unstable temperature, reduced flow and cross-flow. Flush piping before installation and follow the model’s isolation/cleaning instructions. Hard-water buildup may warrant a water-treatment assessment; a softener does not eliminate valve maintenance.
- Inlet or flow problems: reversed supplies, insufficient hot water, a lost cold supply or changing pressures can affect output. A no-flow symptom can involve the valve or its supplies; do not automatically diagnose the heater. Start with the actual supply temperatures and flow.
- Maintenance: both linked Cash Acme manuals recommend checking operation at least annually, more often with adverse water conditions. Recheck at the commissioning outlet and investigate a change greater than 5°F. There is no universal cartridge-replacement interval.
Buying one
Choose the job before the connection. A single low-flow faucet and a heater’s distribution outlet need different sizing. Check the smallest flow the valve will see, hot/cold inlet conditions, service clearance and the locally required protection.
Heater distribution with 3/4-inch female threads: Cash Acme HG110-D 25523
Consider this model when the installer needs 3/4-inch FNPT connections and a valve listed to ASSE 1017 for distribution. Cash Acme also lists ASSE 1069 and 1070, but its location determines which application it serves. Integral inlet checks are included. Plan the matching male-threaded pipe adapters, isolation fittings and temperature measurement separately; this is not a complete heater connection kit.
Skip it as a push-fit replacement. Amazon’s bullets describe disconnect clips and tool-free pipe insertion, but Cash Acme’s model table identifies 25523 as threaded FNPT. It is not the direct SharkBite 24549 variant.
Resolve low-flow sizing before buying. The current February 2026 spec sheet gives a 0.5 GPM minimum; the linked IS291 Rev C installation manual gives 1 GPM. Do not rely on the lower number without Cash Acme confirming it for the supplied valve. The manual also requires hot inlet water at least 27°F above the desired setting. Have the installer check the actual inlet conditions rather than simply turning the heater to 140°F.
View Cash Acme HG110-D 25523, 3/4-inch FNPT, on Amazon
One sink with 3/8-inch compression supplies: Cash Acme HG145 24524
Choose this ASSE 1070 point-of-use valve for an individual faucet when its flow and inlet conditions fit the maker’s requirements. Its compression connections suit 3/8-inch outside-diameter tube, not 3/8-inch pipe threads. It includes integral hot/cold inlet checks, strainer screens and a mounting clamp. Match the supply hoses and any cold-water bypass arrangement separately: 24524 is the plain compression model; 24525 is the separate tee-and-elbow configuration.
The January 2026 specification gives a 95–118°F adjustment range and 0.34 GPM minimum operating flow. Skip this model for whole-house distribution or a faucet running below that minimum. Amazon’s 85–130°F and push-to-connect bullets do not match this model; use the HG145 specification and the instructions supplied with your valve. The available manual differs from the current sheet on some inlet, factory-setting and maximum-flow figures, so confirm those limits with Cash Acme for your installation.
View Cash Acme HG145 24524, 3/8-inch compression, on Amazon
Commissioning is part of the purchase. Both linked manuals call for a thermometer check at the nearest supplied outlet, at least 1.5 GPM during adjustment, and at least one minute for stabilization. That commissioning flow is different from the operating minimum; confirm an approved procedure if your fixture cannot provide it. Follow the supplied instructions and local limits, then record the measured temperature for maintenance. Our connection guide explains why compression and push-fit parts are not interchangeable.
Warranty: RWC’s current policy lists five years for Cash Acme thermostatic mixing valves for installations after May 1, 2026, subject to its installation, use and claim conditions. Keep proof of purchase. The older HG145 manual states 12 months, so use the policy applicable to your installation date and confirm coverage with RWC. Repair/replacement is conditional; removal, reinstall labor and consequential costs are generally excluded except where the policy expressly provides otherwise.
Availability checked October 6, 2026: both exact models were orderable and sold by Amazon.com. Seller and stock can change.
FAQ
What does a thermostatic mixing valve do?
It blends hot and cold water to regulate the mixed outlet temperature within its specified inlet and flow conditions. A distribution valve controls the hot-water system supply; a point-of-use valve limits the supply to a fixture. Choose the appropriate listing and placement.
Can I just turn my water heater down instead?
Many homes use a lower storage setting. CPSC recommends 120°F to reduce residential scald risk, while CDC discusses higher storage temperatures for germ control together with burn protection and individual healthcare advice. A mixing valve does not disinfect water or make a higher setting appropriate for every home.
What temperature should tap water be limited to?
The 2024 IPC sets 120°F maximum delivery for individual shower/tub-shower and bathtub/whirlpool applications in sections 412.3 and 412.5, with the required devices and field adjustment. Check your locally adopted code and the valve instructions. A code maximum is not a guarantee against burns.
Is a mixing valve the same as an anti-scald shower valve?
No. ASSE 1017 applies to distribution temperature control; ASSE 1070 applies to fixture temperature limiting and does not provide thermal-shock protection. An individual shower/tub-shower needs its compliant compensating valve. A distribution valve’s multiple listings do not let it replace required fixture controls.
Where does a whole-house mixing valve get installed?
A distribution mixing valve is installed at or near the hot-water source, with hot and cold inlets and a mixed outlet feeding the distribution piping. It needs appropriate flow sizing, commissioning and service access. A point-of-use valve serves its specified fixture application instead.
Sources
- ASSE — Temperature Control Devices in Domestic Hot Water Systems: Pages 7, 11 and 13 distinguish distribution, fixture limiting and multiple listings; this white paper is application guidance, not your locally adopted code.
- ICC — 2024 IPC, Chapter 4: Sections 412.3 and 412.5; check local adoption and amendments.
- Georgia DCA — Current State Minimum Codes: Current state adoption and amendment links.
- Cash Acme HG110-D specification: Rev 2.0, February 6, 2026; exact 25523 connection and listings.
- Cash Acme HG110-D installation instructions: IS291 Rev C; inlet conditions, commissioning, annual checks and troubleshooting. Minimum flow differs from the current specification, as disclosed above.
- Cash Acme HG145 specification: Rev 2.0, January 12, 2026; 24524/24525 configurations, operating minimum and adjustment range.
- Cash Acme HG145 installation instructions: IS316; commissioning and maintenance. Some figures and the warranty differ from newer documents, as disclosed above.
- Cash Acme HG135/HG145 service guide: Strainer/check service and included model-specific components.
- RWC limited warranty: Updated April 2026; applies to installations after May 1, 2026, with conditions and exclusions.
- CPSC — Tap Water Scalds: Residential setting and prolonged-exposure risk.
- CDC — Preventing Waterborne Germs at Home: Home heater temperatures, burn protection and individual risk advice.
- Watts — Thermostatic Mixing Valves: Model-specific inlet limits, source/fixture distinction, isolation and flushing.