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Legionella thrives in the warm, standing water inside conventional storage tanks. Noritz commercial tankless systems heat water on demand — no reservoir to stagnate, no lukewarm zone to colonize, and precise high-temperature delivery on every draw.
Legionella bacteria multiply fastest in warm, still water. A conventional storage water heater creates exactly that environment — and holds it, gallon after gallon, around the clock.
Illustrative temperature zones. Growth range and disinfection thresholds reflect widely cited public-health guidance; confirm against local code and your water management plan.
Legionella proliferates roughly between 77°F and 113°F. Tanks held at moderate setpoints — or with cooler bottom layers — park water right in that range.
Dozens or hundreds of gallons sit idle between draws. Low-demand periods — nights, weekends, seasonal buildings — let bacteria and biofilm establish.
Sediment and scale on tank walls form biofilm that protects Legionella from disinfection and reseeds the system after treatment.
Take away the reservoir, the stagnation, and the lukewarm setpoint, and you take away the environment the bacteria depend on.
Water is heated as it flows through the unit — there's no stored volume sitting idle for bacteria to multiply in.
Every draw pulls fresh supply water and heats it in real time, so the system isn't recirculating a standing batch.
Tight setpoint control lets you deliver water at temperatures that discourage growth, paired with mixing valves for safe fixture output.
Multi-unit racks scale capacity without oversized storage, and let you service one unit while the rest keep the building supplied.
Schematic of the flow-through heating path. Simplified for illustration — not a plumbing or gas-fitting diagram.
When a fixture opens, cold supply water flows through a high-efficiency heat exchanger and is brought to setpoint in seconds. When the draw stops, so does the heating. There is no batch of warm water waiting in a tank between uses.
The result is a domestic hot water plant with far less standing volume — the single biggest reservoir for Legionella in most buildings is simply removed from the design.
Removing the tank is the foundation — but a defensible water management plan considers the full distribution system. Noritz systems are engineered to support it:
Consistent, controllable delivery temperatures to support thermal management strategies.
Compatibility with recirculation loops and mixing valves for balanced, code-compliant distribution.
Right-sized capacity that eliminates the oversized storage many buildings no longer need.
Tankless design substantially reduces the standing-water conditions associated with Legionella growth. It is one component of a building water management program under ASHRAE 188 — not a standalone substitute for one.
The NCC199CDV is Noritz's flagship commercial condensing tankless unit. A single unit delivers high-efficiency, on-demand hot water — and multiple units link into a rack-mounted multi-system that scales to the largest commercial loads without reintroducing bulk storage.
| Specification | Value |
|---|---|
| Model | NCC199CDV |
| Type | Indoor/outdoor commercial condensing tankless, direct vent |
| Max Gas Input | 199,900 BTU/h |
| Min Gas Input | 12,800 BTU/h (modulating) |
| Max Flow Rate | 11.1 GPM |
| Energy Factor | 0.98 UEF |
| Fuel | Natural Gas or Liquid Propane |
| Venting | 2″, 3″ or 4″ PVC / CPVC (Sch 40/80) or PP; direct-vent, single-vent convertible, or outdoor |
| Multi-System | Up to 24 units with a system controller (up to 8 via Quick Connect Pro) |
Additional specifications: 26.1″ H × 18.1″ W × 11.8″ D, 62 lb · 0.71 gal water-holding capacity · temperature range 100–185°F · 16:1 turndown ratio · 10-year heat-exchanger, 5-year parts, and 1-year labor commercial warranty. Source: Noritz NCC199CDV specification sheet (Rev. 12/2025).
No water heating technology eliminates Legionella on its own. Tankless removes the largest contributing factor in most systems — a warm, standing storage volume — which substantially lowers risk. Fixtures, dead legs, recirculation lines, and low-use branches still require attention as part of a building water management program.
Legionella multiplies most readily in water roughly between 77°F and 113°F (25–45°C). It becomes progressively inactive at higher temperatures, with rapid die-off above about 140°F (60°C). Storage tanks frequently hold water within or near the growth range, especially in cooler bottom layers.
ASHRAE Standard 188 calls for identifying and controlling conditions that allow waterborne pathogens to grow. Tankless supports that goal by reducing standing water and enabling consistent temperature control. It is one engineered element within the broader plan, which also covers distribution, monitoring, and remediation procedures.
Yes. Multiple units are combined into manifold systems that scale to the peak simultaneous demand of hotels, multifamily, healthcare, and institutional buildings — without the oversized storage a tank system would require. Redundancy also lets you service one unit while the rest maintain supply.
Talk with a Noritz commercial specialist about your building's hot water demand, or start speccing a tankless system engineered to reduce standing-water risk.