AC Inline Duct Fan for HVAC Ventilation: 556 m3/h Case Study

What the ventilation OEM needed

The enquiry was almost a purchase order. An HVAC OEM wanted approved specification sheets and drawings for two sizes of AC inline duct fan. Furthermore, it was ready to buy as soon as we confirmed the numbers.

Here the fans go into a new range of light commercial ventilation units on 220 VAC, 50 Hz. One 4-inch model at 100mm, and one 6-inch model at 150mm.

Four constraints defined the job.

• Around 550 m3/h from the 6-inch unit, and about 300 m3/h from the 4-inch.
• Static pressure above 300 Pa, because ductwork and filters both eat pressure.
• Noise below 40 dB(A), since these units run in occupied rooms.
• A 320mm length limit on the 6-inch fan, since the housing was already designed.
• CE marking, together with RoHS and REACH, for the European market.

The pressure requirement is the one people underestimate. An AC inline duct fan that makes 550 m3/h in free air may make almost nothing once you attach a filter and ten meters of duct.

Specifying the AC inline duct fan

This was, in short, a selection job rather than a development job. Not every enquiry needs an NPI cycle. Treating this one as custom would simply have wasted the customer’s time.

The LWDA series fits the brief

Our LWDA series is built for exactly this market. It covers high-volume residential and light commercial ventilation, where cost, airflow and noise all have to land together.

Why we did not propose EC

We considered a SmartEC motor and set it aside. EC is certainly more efficient, and it gives proper variable speed. However, the customer system uses a simple high/low switch. A two-speed AC inline duct fan does that job perfectly well for less money. Fitting an EC fan would only have added 0-10V or PWM signaling the client architecture cannot use. Selling somebody a feature their product cannot reach is not good engineering.

Why the housing is plastic

We ruled out a steel case for similar reasons. The PBN plastic housing resists corrosion indoors, weighs less on an installer ladder, and costs meaningfully less than steel. In a damp ceiling void, moreover, plastic is arguably the better material anyway.

The impeller choice

Both models, LWDA-100(4″)S-PBN-003-12 and LWDA-150(6″)S-PBN-002-12, use a mixed-flow impeller. That is a deliberate compromise. A mixed-flow wheel builds pressure rather like a centrifugal blower, yet it keeps the straight-through airflow path of an axial fan. In a duct, that combination is hard to beat.

Finally, a two-speed AC external rotor motor supplies the high and low settings. On high, the 150mm model gives 556 m3/h at 309 Pa and 38 dB(A). In short, it clears the brief with room to spare. Its IP44 rating covers dust and splashing water, which most HVAC installations need at some point.

Technical Specifications

Two models are listed side by side below, the 100mm and the 150mm. Each has a high and a low setting, so read the columns in pairs rather than singly.

Technical Documentation

Meanwhile the following documents were approved and delivered to the customer, enabling them to finalize their system design and proceed with procurement.

Consolidated Specification Sheet (PDF)
Here the document provides the full electrical and aerodynamic performance data for both models, essential for procurement managers and system engineers to confirm product-application fit.

Technical Drawing & Performance Curves (PDF)
This file contains detailed mechanical drawings with all critical dimensions for CAD integration, along with P-Q curves for accurate operating point analysis.

The specified LWDA-150(6″) AC Plastic Inline Duct Fan.

The specified LWDA-100(4″) AC Plastic Inline Duct Fan.

Why the OEM ordered from us

For high-volume OEM work, the fan is only half the decision. In this case, four other things mattered.

• Documents that arrive quickly. The client basically needed approved files to raise a purchase order. Our workflow moved it from enquiry to final deliverables fast, and that keeps an OEM production schedule intact.
• Cost engineered in deliberately. A proven two-speed AC motor and a light plastic housing meet every requirement, yet the price sits materially below European-branded equivalents. In light commercial HVAC, that decides tenders.
• Reliability you can put in a submittal. We verify performance to ISO 5801. Likewise the S1 continuous duty rating and 50,000-hour L10 bearing life are documented rather than implied.
• Certification already done. Every AC inline duct fan here ships with CE, FCC, RoHS and REACH as standard. Therefore the OEM adds no certification cost or delay of its own.

Browse our inline duct fan range, or the EC inline duct fan series if you need variable speed rather than an AC inline duct fan on high/low. Bathroom wiring zones are set out in IEC 60364-7-701.

Questions installers and buyers ask

What is the difference between the high and low settings?

High runs at 2600 RPM and draws 80W, giving 556 m3/h and 309 Pa. Low runs at 2200 RPM on 70W, giving up to 400 m3/h and 171 Pa. It is also noticeably quieter. Consequently you get demand-based ventilation without buying a separate speed controller.

Can these go in a bathroom or wet room?

Yes. Both models are IP44, so they resist solids over 1mm and splashing water from any direction. Consequently they suit zone 2 and outside-zone positions in bathrooms and similar humid spaces, provided the installation follows local wiring rules such as IEC 60364-7-701.

Can I fit a TRIAC or thyristor speed controller?

Please do not. These AC external rotor motors are impedance protected and wound for two specific speeds. A phase-angle controller makes them hum, run hot and fail early. It also voids the warranty. Where you genuinely need variable speed, choose an EC inline duct fan with 0-10V or PWM control built in.

Will 309 Pa be enough for my duct run?

It depends on the run, not on the AC inline duct fan. First add up the duct resistance, the bends, the grille and the filter. Then read the curve at that pressure rather than at free air. If the total exceeds roughly 250 Pa, size up instead of running the fan at the end of its curve.