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Water Safety & Flow Control

OneFlow® Model OFTWH Anti-Scale System

The Intelligent Scale Solution™ for Tankless Water Heaters

Tankless water heaters with tightly packed, gauge tubing are prone to overheating and malfunctioning, resulting in scale formation. The OneFlow™ Model OFTWH resolves this problem. With the same water treatment technology that's been used successfully in commercial plumbing, the OneFlow™ Model OFTWH is designed to ensure scale-free tankless heater operation in your home or small business. The OFTWH model is a cost-effective solution that prevents scale by turning dissolved hardness minerals into tiny, benign crystal particles that don’t attach themselves to your pipes, valves, fixture and other elements of your plumbing system, a common problem among residential building owners, property managers, and facility engineers.


  • Compatible with all major tankless water heater brands
  • Maintains manufacturer's stated water heater efficiency
  • Works to prevent heater malfunction due to scale build-up
  • Diminishes existing scale problems and costs associated with de-scaling
  • Environmentally friendly alternative to water softeners
  • Almost zero maintenance required due to no salt of chemicals needed
  • No backwashing or electricity needed

Pressure – Temperature

  • Maximum Pressure: 90psi/620.1 kPa
  • Maximum Temperature: 100ºF/38ºC
  • Minimum Temperature: 35ºF/2ºC

Inlet/Outlet Connections

  • ¾ in. FNPT

Service Flow Rate

  • 0.5 gpm to 10 gpm (1.9 Ipm to 38 Ipm)

Gallon Rating:

  • OFTWH: up to 6 gpm, 24/7/365 for 2 years for the OFTWHRM.
  • Designed specifically for tankless water heaters with up to ten gallons a minute
  • Easy sizing & installation with standard ¾ connections, including mounting bracket
  • Simple shutoff and filter change with inlet ball valve and filter wrench
  • Only change OneFlow™ cartridge every 2 years

A Breeding Ground for Scale

Hard scale can accumulate over time on pipes, valves, fixtures and heating elements. Heat increases the tendency for limescale deposits to form; the higher the heat the greater the buildup. Tankless hot water heaters, designed to operate at high efficiency, can be a breeding ground for scale. Once formed, these scale deposits result in malfunctions and calls for service.

Single Cartridge; Easily Installed

The OneFlow® Anti-Scale System provides protection from scale formation on internal and external plumbing surfaces. The OneFlow® Model OFTWH is a single cartridge-based system that is easily installed on a cold water line prior to a tankless water heater. Once installed, the system requires very little maintenance, no backwash, no salt and no electricity. It is truly The Intelligent Scale Solution™.


To learn more about OneFlow® anti-scale technology and how it can solve your scale problems, visit or contact your Watts representative.



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