Chilled water fan coil system
Your heat pump already makes cold water. We help you use it.
Most heat pumps can chill water down to 5°C. Our fan coil kits take that chilled water and turn it into cool air for every room. Per-room controls, timers, and whisper-quiet operation.
How it works // animated
The science
How heat pumps make cold water
Your heat pump works by moving heat from one place to another. In winter it extracts heat from outside air and puts it into your water. In summer, it reverses — extracting heat from your water and rejecting it outside. The result: water chilled to as low as 5°C, returning at 12°C after absorbing room heat.
Flow temperature
Chilled water from your heat pump enters the fan coil unit at 5°C. This is the same process your heat pump uses for heating — just reversed.
Return temperature
Water returns to the heat pump at 12°C after absorbing heat from the room air. That 7°C delta is your cooling capacity at work.
Cooling output
Our HFC range covers 1.9kW for a bedroom to 3.7kW for large open-plan spaces. That's equivalent to a portable AC — without the noise, hose, or running costs.
The problem
Why your radiators can't cool your home
Your heat pump can make cold water. So why not just run it through your existing radiators? Three reasons — and they're all physics.
No air movement
Radiators work for heating because hot air rises naturally, creating convection currents that circulate warmth around the room. Cold air does the opposite — it sinks and pools at floor level. A cold radiator just creates a thin layer of cool air at your feet while the rest of the room stays hot.
Condensation everywhere
When a surface drops below the dew point, moisture in the air condenses on it — exactly like a cold glass on a summer day. A radiator running 5°C water will drip with condensation. No drain tray, no way to manage the water. You'd end up with puddles on the floor and damp on the walls.
Tiny surface area
For heating, radiators push water at 45–55°C into a 20°C room — a 25–35°C temperature difference driving heat transfer. For cooling, it's 5°C water into a 25°C room — only a 20°C delta. Less temperature difference means less heat exchange, and radiators don't have nearly enough surface area to compensate.
A fan coil unit solves all three problems. A fan forces air across the cold heat exchanger, actively mixing cool air into the room. A built-in drain tray catches all condensation and pipes it away. And the heat exchanger's densely packed fins give you far more surface area than a radiator in a fraction of the space.
System features
Not just a fan in a box
Per-room temperature control
Each room gets its own thermostat. Bedroom at 18°C, living room at 22°C. Each unit runs independently so you only cool the rooms that need it.
Timers & scheduling
Cool bedrooms before you sleep, living areas during the day. Set schedules per room so you only cool what you need, when you need it.
Whisper quiet
The fan coil sits in the loft, away from living spaces. All you hear in the room is a gentle breeze from the ceiling vent. No compressor noise, no vibration.
Fraction of the running cost
Your heat pump has a COP of 3–5 for cooling. That means for every 1kW of electricity, you get 3–5kW of cooling. A portable AC gets you about 1kW for 1kW.
No planning permission
Entirely internal installation — no external units, no external alterations. Ideal for listed buildings and conservation areas. Uses your existing heat pump.
Installation sequence
How it works
Each room gets its own fan coil unit in the loft, fed by chilled water from your heat pump. Cool air drops through a short duct to a ceiling vent — one unit, one room, independent control. You can run a single unit to two rooms if needed, but dedicated units give the best performance.
System diagram
Pipe from heat pump
Chilled water pipes run from your heat pump up to the loft, with a flow and return branch for each fan coil unit. Same pipework your heating uses — just colder water.
One unit per room
Each room you want to cool gets its own fan coil unit sitting on loft joists. 5°C water flows through the heat exchanger while a fan blows air across it.
Short duct to ceiling vent
A short insulated duct drops cool air from each unit down to a ceiling vent in the room below. No long duct runs, no complex routing.
Room thermostats
Each unit has its own thermostat and timer. Set the temperature and schedule per room. The system does the rest.
Product range
One unit per room, three sizes
Bedrooms & offices
One unit, one room, one ceiling vent. Perfect for a bedroom or home office. Enough output to cool a room up to ~15m².
Living rooms
For larger rooms that need more capacity. Can also serve two smaller rooms with a dual-duct setup, though dedicated units per room give better control.
Open plan spaces
For large open-plan living areas, kitchen-diners, or rooms with high ceilings that need serious cooling capacity.
Honest sizing
Realistic cooling output
Most fan coils are quoted at a single figure rated with 6–7 °C chilled water — colder than most heat pumps actually run. This shows what each HFC unit really delivers at your system's flow temperature and room conditions.
Your system
Your heat pump's cooling flow temperature.
~27 °C for a hot room being pulled down; ~24 °C for steady comfort.
Affects whether the coil dehumidifies.
Output at your conditions
ETD ×0.85 · Fan ×1.00
At 7.0 °C flow, the coil runs below the room dewpoint (14.4 °C) — it will dehumidify and produce condensate, which must be drained.
HFC-19
HFC-28
HFC-37
Sensible cooling
Drops the air temperature.
Heat moves from the room air into the cold coil, so the air leaves the unit colder than it arrived. This is the bit you read off the thermostat — the temperature drop you actually feel.
Latent cooling
Takes water out of the air.
When the coil is colder than the room dewpoint, water vapour condenses onto it and drains away. The energy goes into turning vapour into liquid, not into a temperature drop — but the room ends up drier. Dry air feels much cooler than humid air at the same temperature, and it stops that sticky, muggy summer-night feeling. A wet coil must be drained.
Install note — pipes must be insulated
Any pipe carrying chilled water is well below the room dewpoint and will sweat exactly like the coil does — even when the coil itself is dry. Every metre of chilled-water pipe between the heat pump and the fan coil units must run in closed-cell pipe insulation with sealed joints. Skip this and you'll get condensation dripping inside ceilings, walls, and onto floors.
Rated at EWT 7 °C / air 27 °C. Sensible figure assumes ~70% sensible heat ratio when the coil runs wet. Figures are first-order engineering estimates based on entering-temperature-difference scaling, not manufacturer selection-software output, and assume the rated chilled-water flow rate through each unit. Use for guidance and sizing sanity-checks, not as a guaranteed performance figure.
Every heat pump sold in the UK can produce chilled water. Almost none of them are being used for cooling. We're building the missing piece — a simple kit that connects to what you already have and gives you room-by-room cooling for a fraction of the cost of a split AC system.
Simon Bennett
Founder
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HFC-19, HFC-28, and HFC-37 chilled water fan coil units. Load-compensated control. Designed for UK heat pump installations.
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