A PSC motor and an EC motor both turn the blower in a fan coil unit. The difference is efficiency, and it grows as speed drops. On a 600 CFM unit at 12 Pa external static pressure, our AC motor drew 96 W at high speed, 84 W at medium and 70 W at low. The EC replacement drew 52 W, 26 W and 13 W. At medium speed that is a 69% reduction. Whether it pays back depends on one number: how many hours the unit runs.
The short version
| Aspect | PSC (induction) | EC (BLDC + drive) |
|---|---|---|
| How it runs | Mains AC, capacitor creates the rotating field | Mains rectified, electronics commutate a permanent-magnet rotor |
| Typical efficiency | 30–50%, less at low speed | 70–80%, held across the speed range |
| Speed control | Winding taps — usually three fixed speeds | Stepless via 0–10 V, PWM or remote signal |
| Heat into the airstream | Higher — the losses end up in the air | Roughly half the loss for the same duty |
| Weak point | Bearings | The drive electronics |
| First cost | Lowest | Higher |
Two motors, one job
A PSC motor is a single-phase induction motor with a run capacitor. It needs nothing but mains power, has no electronics, and is cheap to build — which is why it has been the default in fan coil units for decades. Speed control is coarse: three winding taps, three speeds.
An EC motor is a brushless DC motor with the controller built into the housing. Magnets produce the field instead of induced rotor current, so most of the loss that limits an induction motor disappears. Our EC motor for fan coil units is rated 80 W at 1,350 rpm on 198–242 VAC with efficiency above 70% and a controller MTBF of 50,000 hours; the resin-packed version reaches above 75%. Speed is continuous and takes a signal.
Measured: one duty point, three speeds
The figures below come from a 600 CFM fan coil unit at 12Pa external static pressure, measuring the input power of the motor at each of the three speeds. Same unit, same airflow, same static pressure — only the motor changes.
| Speed | AC motor | EC motor | Reduction |
|---|---|---|---|
| High | 96 W | 52 W | 45.8% |
| Medium | 84 W | 26 W | 69.0% |
| Low | 70 W | 13 W | 81.4% |
Read the bottom row first. At low speed the EC motor draws 13 W where the AC motor draws 70 W — 81% less. That is the band where most fan coil units spend most of their running hours, and it is the band where an induction motor is furthest from its design point.
At high speed the gap narrows to 45.8%, because a PSC motor at full speed is at its most efficient. This is why a comparison done only at rated conditions understates the case for EC: the saving is smallest exactly where the unit runs least.
Where the difference actually shows up
Part load. At full speed the gap is real but not dramatic. It widens as speed drops, and most fan coil units spend most of their life at part load. Two effects compound: the EC motor’s efficiency curve is flatter, and its speed is held by the drive while the PSC motor’s speed sags as the filter loads and static pressure rises — it delivers less air exactly when it is working harder.
Heat. Every watt of motor loss ends up in the airstream, and in a cooling application that heat is load the coil has to remove. At medium speed the AC motor draws 84 W and the EC motor 26 W for the same airflow, so roughly 58 W less heat enters the air. On a 2.5 kW unit that is about 2% of capacity — small on one unit, and multiplied by every unit, every hour the building is occupied.
Noise. An EC motor is generally quieter at low speed, because it can run slower without stalling. It will not fix a noisy unit — blade pass tone, duct resonance and mounting stiffness usually dominate.
Service life. A PSC motor’s limit is its bearings; there is nothing else to fail. An EC motor adds a controller, and its capacitors are what age in heat. In a hot ceiling void, check the controller MTBF and the ambient rating, not the headline efficiency.
Retrofit: what has to match
Replacing a PSC motor with an EC motor usually works, and the failure points are mechanical rather than electrical. Confirm frame diameter and length, shaft diameter and D-cut or keyway, direction of rotation, lead length and exit side, and clearance for the drive where the capacitor used to sit. If the unit has no 0–10 V or PWM signal, use a three-speed EC motor that is switched by mains. The capacitor is always removed — leaving it connected is a common installation error.
When the payback works
Payback (years) = premium ÷ (saving in W × hours per year × price per kWh ÷ 1000)
Take the medium-speed figure: 84 W against 26 W is 58 W saved. On 3,000 run hours a year that is 174 kWh; at 0.25 per kWh, about 43.5 a year. A 30 premium is repaid in under nine months. At low speed the saving is 57 W and the arithmetic is much the same; at high speed it falls to 44 W.
Change one input and the answer moves. At 800 run hours the same motor takes about two and a half years instead of nine months. At 6,000 hours it pays back in under five months. This is why “EC is more efficient” is not by itself an argument — the argument is the run hours and the speed the unit actually runs at.
When a PSC motor is still the right choice
- The unit runs a few hundred hours a year, so the saving never repays the premium.
- The mounting position is hot, condensing or vibration-heavy enough that electronics are a liability.
In those cases the honest recommendation is the AC motor range, not a more expensive motor with a payback the customer will never see.
Questions we get about PSC and EC motors
Q: Can I replace a PSC motor with an EC motor in an existing unit?
A: Yes, if the frame, shaft and mounting match. If no control signal is available, use a three-speed EC motor switched by mains.
Q: Is an EC motor more reliable than a PSC motor?
A: Not automatically. An EC motor adds a controller whose capacitors age in heat, which is why controller MTBF is quoted separately and the ambient rating matters more than the efficiency figure.
Q: Will an EC motor make my fan coil unit quieter?
A: Only if the motor is the dominant noise source. In most units the blower wheel, the duct and the mounting dominate.
Work out the case for your unit
Send us the duty point, the annual run hours and the control signal available at the unit, and we will tell you which motor makes sense for that application — including when the answer is the cheaper one. Start from the EC motor range, the AC motor range, or the mechanical selection guide: How to choose a fan coil unit motor.