The Caleffi 166602A is a HydroMixer 166-series thermostatic mixing unit with a Grundfos ALPHA 25-55U variable-speed pump mounted on the right, providing fixed-point temperature mixing and circulation for a low-temperature radiant zone, with supply and return temperature gauges (dual scale 32-176 °F).
Product data compiled from Caleffi North America technical documentation (01238 NA, NA11018) and the Caleffi North America product catalogue. Last reviewed August 2026.
Key Features
Fixed-Point Thermostatic Mixing
A thermostatic valve holds the zone supply at a constant low temperature for radiant panels - fully mechanical, no controls wiring.
Grundfos ALPHA 25-55U Variable-Speed Pump
Integral Grundfos ALPHA 25-55U ECM high-efficiency circulator mounted on the right.
Supply and Return Temperature Gauges
Dual-scale gauges (32-176 °F / 0-80 °C) on both supply and return show mix temperature and zone delta-T at a glance.
Compact Zone Add-On
A complete drop-in unit for adding a mixed low-temperature zone to an existing boiler system.
Technical Data
| Function | Thermostatic mixing unit (166 series) |
|---|---|
| Circulator | Grundfos ALPHA 25-55U variable-speed |
| Pump orientation | Pump Right |
| Temperature gauges | Supply and return, dual scale 32-176 °F (0-80 °C) |
| Maximum operating pressure | 145 psi |
| Adjustment temperature range | 80-125 °F |
| Electric supply | 115 V AC, 50/60 Hz |
Documentation
Technical brochureRelated Products
Frequently Asked Questions
A HydroMixer 166-series thermostatic mixing unit: a fixed-point mixing valve with integral circulator, check valve, shut-off ball valves, pre-formed EPP insulation shell and supply/return temperature gauges, for adding a low-temperature radiant zone.
A Grundfos ALPHA 25-55U variable-speed pump, mounted pump right.
No. Mixing is fully thermostatic; only the circulator needs 115 V power.
- Type:
- Mixing Unit
- Series:
- HydroMixer
- Pump Type:
- Alpha High-Efficiency Pump
- Configuration:
- Pump Right
