What is the difference between 2-pipe and 4-pipe cassette fan coil units?

A 2-pipe cassette fan coil unit uses a single heat exchanger coil connected to one supply and one return pipe, switching between heating and cooling modes centrally. A 4-pipe unit has two independent coils (one for chilled water, one for hot water) with four pipe connections, allowing simultaneous heating and cooling in different zones from the same system.

Why choose a hydronic cassette FCU over a VRF cassette?

Hydronic cassette FCUs use water instead of refrigerant for heat distribution, eliminating the need for refrigerant piping in occupied spaces. This means no PFAS risk, 95% less refrigerant charge (confined to the outdoor heat pump), lower maintenance costs, longer equipment life of 20+ years, and compatibility with multiple heat sources including heat pumps, boilers, and solar thermal.

Cassette Fan Coil Units — 2-Pipe & 4-Pipe Technical Datasheet

Product Overview

Ceiling-recessed hydronic cassette fan coil units delivering whisper-quiet, 4-way air distribution for hotels, offices, hospitals, and commercial spaces.

The Karnot iZONE Cassette Fan Coil Unit range (HLC 34UE – 238UE) provides efficient, concealed climate control through ceiling-recessed installation with 4-way air distribution. Available in 2-pipe (changeover) and 4-pipe (simultaneous heating/cooling) configurations, these units deliver airflows from 340 to 2,380 m³/h and cooling capacities from 1.8 to 12.6 kW.

Designed for hydronic HVAC systems, iZONE cassette units use chilled or hot water from a central plant (such as the Karnot iHEAT R290 heat pump) eliminating refrigerant from occupied spaces. The result is a PFAS-free, quiet, and highly efficient comfort solution with 20+ year equipment life.

Karnot iZONE 2-Pipe Cassette Fan Coil Unit

2-Pipe System

HLC 34UE – 238UE

Single coil changeover cassette. 9 models, 340–2,380 m³/h airflow, 1.8–12.6 kW cooling, 2.7–19.0 kW heating. Ideal for centralised changeover systems.

Karnot iZONE 4-Pipe Cassette Fan Coil Unit

4-Pipe System

HLC 34UE 4R – 238UE 4R

Independent dual coil cassette with simultaneous heating and cooling. 9 models, 340–2,380 m³/h airflow. Full zone autonomy for mixed-load buildings.

4-Way Air Distribution

Even air delivery across all four sides of the cassette, eliminating hot and cold spots for uniform room comfort.

Concealed Design

Flush ceiling-recessed installation with only the decorative grille visible. Clean aesthetics for premium interiors.

Whisper Quiet

Sound levels from 25 dB(A) on low speed. Ideal for hotel guest rooms, hospital wards, and executive offices.

High Efficiency

Low fan power consumption (9–86 W) combined with optimised coil design for maximum heat transfer per watt.

PFAS-Free

Water-based distribution eliminates all fluorinated refrigerants from occupied spaces. Future-proof against F-gas regulations.

Smart Ready

Compatible with BMS integration, wired/wireless thermostats, and smart scheduling. Zone-level control for every room.

2-Pipe Cassette Specifications

Single coil changeover system — 9 models from HLC 34UE to HLC 238UE

Parameter	HLC 34UE	HLC 51UE	HLC 68UE	HLC 85UE	HLC 102UE	HLC 136UE	HLC 170UE	HLC 204UE	HLC 238UE
Air Flow
High (m³/h)	680	680	1,020	1,020	1,360	1,700	2,040	2,380	2,380
Medium (m³/h)	510	510	850	850	1,020	1,360	1,700	2,040	2,040
Low (m³/h)	340	340	510	510	680	1,020	1,360	1,700	1,700
Cooling Capacity
Total Capacity (kW)	1.8	2.7	3.6	4.5	5.4	7.2	9.0	10.8	12.6
Sensible Capacity (kW)	1.3	1.9	2.6	3.2	3.8	5.1	6.4	7.6	8.9
Water Flow Volume (L/h)	310	464	619	774	929	1,238	1,548	1,857	2,167
Water Pressure Drop (kPa)	8	16	12	18	11	18	14	19	25
Heating Capacity
Total Capacity (kW)	2.7	4.1	5.4	6.8	8.1	10.8	13.6	16.3	19.0
Water Flow Volume (L/h)	464	696	929	1,161	1,393	1,857	2,322	2,786	3,250
Water Pressure Drop (kPa)	16	34	26	39	24	39	30	41	54
Performance
Fan Power Input (W)	9	9	18	18	28	42	54	86	86
Sound Level (H/M/L) dB(A)	33/29/25	33/29/25	37/34/30	37/34/30	38/34/31	40/36/33	42/39/35	44/42/38	44/42/38
Dimensions & Weight
Unit Dimensions (mm)	575 × 575 × 260		820 × 820 × 260		820 × 820 × 260	820 × 820 × 260	960 × 960 × 260	960 × 960 × 260
Panel Dimensions (mm)	660 × 660 × 50		950 × 950 × 50		950 × 950 × 50	950 × 950 × 50	1,100 × 1,100 × 50	1,100 × 1,100 × 50
Unit Weight (kg)	13	13	18	18	20	22	28	33	33

4-Pipe Cassette Specifications

Independent dual coil system for simultaneous heating and cooling — 9 models from HLC 34UE 4R to HLC 238UE 4R

Parameter	HLC 34UE 4R	HLC 51UE 4R	HLC 68UE 4R	HLC 85UE 4R	HLC 102UE 4R	HLC 136UE 4R	HLC 170UE 4R	HLC 204UE 4R	HLC 238UE 4R
Cooling Capacity
Total Capacity (kW)	1.7	2.5	3.3	4.1	5.0	6.6	8.3	9.9	11.6
Sensible Capacity (kW)	1.2	1.8	2.4	2.9	3.5	4.7	5.9	7.0	8.2
Heating Capacity
Total Capacity (kW)	2.5	3.8	5.0	6.3	7.5	10.0	12.5	15.0	17.1
Water Flow Volume
Cooling (L/h)	292	430	567	705	860	1,135	1,427	1,703	1,994
Heating (L/h)	429	653	859	1,082	1,289	1,718	2,148	2,577	2,939
Water Pressure Drop
Cooling Coil (kPa)	7	14	10	16	10	16	12	17	23
Heating Coil (kPa)	14	31	23	35	22	35	28	38	48
Performance & Dimensions
Fan Power Input (W)	9	9	18	18	28	42	54	86	86
Sound Level (H/M/L) dB(A)	33/29/25	33/29/25	37/34/30	37/34/30	38/34/31	40/36/33	42/39/35	44/42/38	44/42/38
Unit Dimensions (mm)	575 × 575 × 260		820 × 820 × 260		820 × 820 × 260	820 × 820 × 260	960 × 960 × 260	960 × 960 × 260
Unit Weight (kg)	14	14	20	20	22	24	30	36	36

Operating Conditions & Technical Notes

Standard test conditions, controller features, and installation specifications

Standard Test Conditions

Cooling: Entering air 27°C DB / 19.5°C WB, water inlet 7°C, outlet 12°C
Heating: Entering air 20°C DB, water inlet 50°C, outlet 45°C
Water-side pressure drop measured at nominal flow rate
Sound levels measured at 1.5 m below unit in anechoic conditions
Performance data at High fan speed unless otherwise stated

Controller Features

Wired or wireless thermostat compatibility
3-speed fan control + Auto mode
Heating/Cooling/Auto changeover modes
7-day programmable timer (with compatible controller)
BMS integration via Modbus RTU or 0–10V signal
Condensate pump optional on all models

Installation Specifications

Power supply: 220–240V / 1Ph / 50Hz
Water connections: 3/4” BSP (34UE–85UE), 1” BSP (102UE–238UE)
Condensate: 25 mm OD gravity drain
Ceiling void: minimum 300 mm clearance recommended
Ceiling tile: standard 600 × 600 mm or 950 × 950 mm panel
Refrigerant: None — water only (PFAS-free)

Why Choose Hydronic Cassette FCUs?

9 reasons architects, engineers, and building owners specify iZONE cassette fan coil units

Zero Refrigerant in Rooms

Water-only distribution eliminates refrigerant leak risk in occupied spaces. No PFAS, no F-gas compliance burden per room.

30% More Efficient

Hydronic systems transfer heat 4x more effectively than refrigerant-based splits, delivering 30% energy savings vs. VRF/split AC.

20+ Year Lifespan

No compressor, no refrigerant, no complex electronics. Simple fan-and-coil design lasts decades with minimal maintenance.

True Zone Control

Individual room temperature control with independent thermostats. Heat and cool different zones simultaneously with 4-pipe systems.

Ultra-Quiet Operation

From 25 dB(A) on low speed — quieter than a whisper. Essential for hotel guest rooms, hospitals, and premium offices.

Multi-Source Compatible

Works with heat pumps, boilers, chillers, solar thermal, and district energy. Switch heat source without replacing FCUs.

Simple Maintenance

Washable filters, no refrigerant checks, no F-gas technician required. Building staff can service units in minutes.

Concealed Aesthetics

Flush ceiling-mount with decorative panel. Only the grille is visible — no wall-hung indoor units or exposed pipework.

BMS & Smart Integration

Modbus RTU, 0–10V, and wireless thermostat support. Full building management system integration for centralised monitoring.

The Karnot Ecosystem

iZONE cassette fan coil units are designed to work seamlessly with the complete Karnot product range, creating a fully integrated, PFAS-free hydronic HVAC system.

iHEAT R290 Heat Pumps iCOOL CO₂ Refrigeration iSTOR Buffer Tanks iMESH Hydronic Distribution iSAVE Energy Monitoring iZONE Fan Coil Units