OneFlow® Model OFTWH Anti-Scale System

The Intelligent Scale Solution™ for Tankless Water Heaters

Tankless water heaters with their tightly packed, small gauge tubing are prone to the overheating and malfunction that result from scale formation.

Today there's a solution to this problem – OneFlow® Model OFTWH. The same water treatment technology that’s been used successfully in commercial plumbing is now designed to ensure scale-free tankless heater operation in your home or small business.


  • 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

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 for tankless water heaters up to 10 gallons per minute
  • Virtually maintenance free - no salt or chemicals to add or maintain
  • No Electricity or backwashing required
  • Simple sizing & installation with standard ¾ in. connections and included mounting bracket
  • Inlet ball valve and filter wrench for easy shutoff and filter changes
  • Long lasting OneFlow® cartridge – change once every two 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.



How to Buy

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Additional Information

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