Why Companion? Why CWIS™?

Companion’s design provides as much as 10% greater operating efficiency when compared to other “high efficiency” self-contained heaters. Its unique use of CWIS™ eliminates flow rate restrictions that are common in tankless heaters.



  • Space saving design, up to 99.8% efficiency
  • Inputs ranging from 129,000 BTU to 630,000 BTU/hr
  • Storage ranging from 80 gallons to 160 gallons (not all tanks fit all BTU capacities)
  • Modulating burner with 5:1 turndown ratio
  • Patented Cold Water Injection System (CWIS™)
  • Stainless steel or optional glass-lined insulated tank (less than 1˚F temp loss per hr)
  • Sealed combustion with PVC or stainless vent and air inlet
  • Combined storage & recovery (modular construction with individually replaceable components)
  • Up to 1432 gallons first hour delivery at 60°F temperature rise
  • 10 Year Limited Warranty—in similar environments, Companion last up to three times longer than conventional self-contained heaters

Indirect Companion. When and Why?

In poor water conditions (combined hardness & TDS of over 25 grains per gallon, or aggressive or acidic water) the Indirect Companion Odd Water™ System eliminates scaling and other factors that contribute to premature failure of a conventional water heating system.


  • Up to 95.5% operating efficiency
  • Impervious to scale build-up and loss of efficiency in hard water areas
  • 316Ti stainless steel heat exchanger and tank
  • Modulating stainless steel burner
  • Self-diagnostic microprocessor controls
  • Sealed combustion
  • Condensate neutralizer
  • CPVC or AL 29-4C stainless vent
  • 15-year heat exchanger warranty
  • 10-year tank warranty


  • Piping manifolds on multiple units
  • Cascade controls on multiple units
  • Common venting on multiple units
  • 119-gallon tank also available with a vented, double wall coil heat exchanger

Custom configurations. Only from Hamilton.

No two buildings are exactly the same. At Hamilton Engineering, we understand this. It’s why we so frequently provide custom Companion configurations, engineered to fit your job-specific domestic hot water needs.

If you have a unique application, Hamilton is ready to design a custom system solution to handle all of your challenges. All of our configurations can include pre-piped Companion with CWIS for easy installations and less downtime.


This custom Companion configuration was designed for building heat, with an indirect zone and tank to produce domestic hot water.

Need higher capacity?

Companions also come in multiunit configurations, like this one, which includes reverse return piping for easier field installations.

*Green stands shown used for fabrication purposes only.

Snow Melt Configuration

Another configuration of the Companion, this system was built to provide snow melt, using a domestic hot water package with a double wall heat exchanger.

*Green stands shown used for fabrication purposes only.