Guide: heat emitters
Radiator or fan coil unit? Heating and cooling with a heat pump
Both are supplied with water from the heat pump or boiler via pipes. A radiator heats quietly and simply, a fan coil heats and cools with a quiet fan. Here you can see what suits which situation.
Graphic: Infra Haustechnik
How radiators and fan coils work
Radiator: Warm heating water flows through the radiator. It releases heat to the room mainly as radiant heat and through natural air movement (convection). There is no fan, no electricity at the unit and hardly any maintenance. It does not cool.
Fan coil unit: The unit contains a heat exchanger through which water flows. A fan blows room air through it. In winter warm water arrives and the unit heats; in summer a reversible heat pump supplies cool water and the unit cools. Because the fan actively distributes the heat, a low flow temperature is enough.
Unlike a split air conditioner, no refrigerant flows in a fan coil, only water. The refrigerant stays in the heat pump.
Radiator and fan coil compared
The key differences at a glance. Costs are described qualitatively only, as they depend heavily on the property.
| Criterion | Radiator | Fan coil unit |
|---|---|---|
| Heating / cooling | Heating only | Heating and cooling (with a reversible heat pump or chiller) |
| Flow temperature | Needs higher temperatures for the same output, except large low-temperature radiators | Delivers high output even at low flow temperatures – ideal for heat pumps |
| Space required | The lower the flow temperature, the larger the radiator | More compact for the same output; wall, floor console, ceiling or ducted unit |
| Noise | Silent | Quiet fan noise, audible depending on the speed; use the night setting in bedrooms |
| Condensate when cooling | Not relevant | Condensate tray and drain or condensate pump required |
| Dew point and insulation | No special requirements | Insulate chilled water pipes vapour-tight, otherwise condensation forms on the pipes |
| Control | Thermostatic valve, simple room control | Room thermostat, fan speeds, timer, often via app or building management system |
| Response time | Slow, even warmth | Quickly noticeable, good for rooms with changing use |
| Maintenance | Bleed occasionally | Clean filters regularly, check condensate tray and drain |
| Electricity at the unit | None | Low, for fan and controls; power connection required |
| Costs (qualitative) | Simple, inexpensive units; existing radiators can often be kept | Unit and installation more complex (power, condensate, insulation), but cooling without a second system |
We determine specific outputs and costs after a heat load calculation and a site visit.
When does which make sense?
The right choice depends on the building, the heat pump and how the rooms are used.
| Situation | Recommendation |
|---|---|
| New build with heat pump | Usually underfloor heating or low-temperature radiators. If you also want cooling, add fan coils in individual rooms. |
| Renovation, radiators in place | Check whether the existing radiators are sufficient at a lower flow temperature. Replace individual radiators that are too small with larger ones or with fan coils. |
| Heat pump with cooling function | Fan coils make proper use of the cooling function: they cool noticeably and drain the condensate in a controlled way. |
| Office, practice, commercial | Fan coils are common here: fast control per room, heating and cooling, also installed in ceilings or parapets. |
| Bedrooms, quiet rooms | Radiators or underfloor heating are silent. A fan coil is possible if it is sized generously and runs at low speed. |
| Heating only, small budget | Radiators remain the simple, robust solution. |
Combination: radiators and fan coils in the same house
Both systems can be connected to the same water circuit of the heat pump. Typically the radiators or underfloor heating remain in the living area, and a fan coil is added in the attic, the office or a very sunny room.
Clean hydraulics are important: when cooling, only the fan coils may receive cold water; the radiators are then isolated with valves. This requires hydraulic balancing and controls that clearly separate heating and cooling mode.
Underfloor heating can provide gentle cooling (free cooling or active cooling), but it does not dehumidify. Fan coils complement it well when more cooling capacity is wanted.
What matters when cooling
Condensate: If the fan coil cools below the dew point of the room air, water forms. It runs into a tray and must be drained via a sloping drain or a condensate pump.
Dew point and insulation: Chilled water pipes and fittings are insulated vapour-tight. Otherwise water drips from the pipes and moisture damage can occur.
Controls: Dew point monitoring, summer/winter switchover and room thermostats ensure that the system runs safely and economically.
Maintenance: Clean the filters every few months depending on use and check the tray and drain during servicing. This keeps the air clean and the unit quiet.
Frequently asked questions
Can I cool with radiators?
Normal radiators are not designed for cooling: they have no condensate drain and no insulation. Fan coils or specially designed surface systems are suitable for cooling with water.
What is a fan coil?
A fan coil unit is a device with a heat exchanger and a fan. It is supplied with water from the heat pump or boiler and can heat and – with cold water – also cool.
Are fan coils suitable for heat pumps?
Yes. Fan coils achieve high output even at low flow temperatures, which benefits the efficiency of the heat pump. If the heat pump is reversible, they can also cool in summer.
Is a fan coil noisy?
You can hear the fan quietly, especially at high speed. Correctly sized, the unit usually runs at low speed and is then very quiet. Radiators are silent.
Is a fan coil the same as an air conditioner?
No. A split air conditioner works with refrigerant in the indoor unit. In a fan coil water flows; the refrigerant stays in the heat pump.
Can I keep my existing radiators?
Often yes. We check whether they are sufficient for the heat pump and only replace radiators that are too small or add fan coils in individual rooms.
What does a fan coil cost?
That depends on output, design, pipe routing, condensate drain and electrical connection. We prepare a reliable quotation after the site visit.
Radiator, fan coil or both? We will advise you
Book a consultation: we check the heat pump, radiators and rooms and propose the right solution. Or write to us at info@infrahaustechnik.ch.