📢 Sound Power (Lw)
The true, absolute noise generated by the machine itself. It does not change whether you place it in an empty room or a furnished one. It is the "raw" truth of the motor - the measurable energy it emits.
Fan Coil Noise (dB): The Truth Behind the Brochures and Sleep in Bedrooms
You bought the best Heat Pump. The water runs perfectly. The room is cool. But the moment you lie down to sleep, the Fan Coil above your head sounds like a jet turbine preparing for takeoff. Noise is the number 1 complaint.
Let us look at how manufacturers "cook" the numbers in technical brochures and why "Low Speed" is the only truth you should be looking at.
1. Sound Power vs Sound Pressure (The Big Trick)
In engineering, noise is measured in two entirely different ways. The confusion between them is the favourite "magic trick" of marketing departments in technical brochures.
👂 Sound Pressure (Lp)
What reaches your ear. It depends on distance, carpets, curtains and furniture (which absorb sound). In an empty room with echo, it sounds louder than in a furnished one.
⚠️ The brochure trap
Many manufacturers print Sound Pressure on the cover (e.g. "Only 21 dB!") measured at 2-3 metres away. In a small bedroom (1 m distance), you will hear +8 to +10 dB more - that is 30 dB!
💡 What to ask for
Always ask the engineer to show you the Sound Power (Lw). It is the only figure that cannot be manipulated by "distance tricks". Compare machines only using this metric.
2. The "Low Speed" Rule
A traditional Fan Coil has 3 fan speeds: High, Medium and Low. Brochures often show performance at Medium or High speed, to make the unit look powerful.
🌙 The reality
In a bedroom, you will never tolerate Medium or High speed. The air whistles. For 90% of its life in the bedroom, the Fan Coil will be forced to run on Low Speed for peace and quiet.
📊 What to check
Check the dB figures only in the "Low Speed" column. Ensure the unit still delivers enough Watts at Low Speed to heat or cool your room adequately.
⚠️ The classic blunder
Many buyers choose an undersized unit that cannot produce enough heat at Low Speed. They are forced to run it on High → noise → cannot sleep. The solution: oversize slightly.
📐 Rule of thumb
Select a Fan Coil with 20-30% more capacity than you need. This way, at "Low Speed" it will fully cover your demand without ever needing to step up.
3. The Sleep Scale (What Is Really "Silent"?)
For a frame of reference, here is the noise scale in relation to sleep (Sound Pressure, measured at 1 metre distance):
🍃 Below 20-22 dB
Rustling leaves. Excellent for sleep. You barely notice it is running. Achieved by top EC motors at minimum speed.
📚 25-30 dB
A whisper or a very quiet library. Perfectly acceptable for most bedrooms. This is what most Fan Coils achieve at Low Speed.
🧊 35-40 dB
Your kitchen refrigerator. Fine for living rooms (with the TV on), but prohibitive for light sleepers. Corresponds to a Fan Coil at Medium speed.
🗣️ Above 45 dB
Normal conversation level. Irritating in any space. A Fan Coil at High Speed or an old model with worn bearings. Avoid units approaching these figures.
4. The Ultimate Solution: EC Inverter Motors (Brushless)
If you want to forget about noise once and for all, demand a Fan Coil with an EC (Electronically Commutated) Inverter Motor. This technology has completely changed the game.
⚡ Old motors (AC)
Had 3 fixed "steps" (like an old pedestal fan). If the room needed just a little cooling, the unit would cycle on/off with noticeable noise at each step change.
🔇 The EC motor (Inverter)
No fixed steps. It modulates speed continuously and silently (from 1% to 100%), depending on what the thermostat demands. When the room reaches temperature, it turns so slowly that nothing is audible.
💰 Electricity savings
The EC motor consumes 50-70% less electricity than its AC equivalent. In 24/7 operation (e.g. a hotel), the savings pay back the cost difference in under 2 years.
🏷️ How to identify
In brochures, look for the terms: EC motor, Brushless DC (BLDC), Inverter fan. If it only says "3-speed" or "AC motor", it is old technology. The cost premium is 15-25% but worth every cent.
🤫 Do not trust the big print! Ask for Sound Power (Lw), check only the Low Speed column, and choose an EC Inverter motor. These 3 rules guarantee peaceful sleep.
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