How to Measure Duct Air Velocity with UNI-T UT366A and Pitot Tube Malaysia

Measuring air velocity inside a ventilation duct helps HVAC technicians evaluate airflow performance, identify restrictions and check whether an air-handling system is operating as intended.

When connected to a compatible Pitot tube, the UNI-T UT366A Digital Manometer can measure the differential pressure created by moving air and display the corresponding air velocity.

How Pitot Tube Airflow Measurement Works

A Pitot tube uses two pressure measurements:

Total pressure, measured by the opening facing the airflow
Static pressure, measured through openings positioned away from the direct airflow

The difference between total pressure and static pressure is called velocity pressure. The UT366A measures this pressure difference and uses it to determine the air velocity.

This method is commonly used for checking airflow inside:

Supply-air ducts
Return-air ducts
Exhaust ducts
Fresh-air systems
Industrial ventilation
Furnace and combustion-air systems

UT366A Wind-Speed Measurement

With the optional Pitot tube connected, the UT366A supports air-velocity measurement in:

Metres per second: m/s
Feet per minute: fpm

The instrument’s official specification lists air-velocity display ranges of up to 19,999.9 m/s and 199,999 fpm. The practical measurement result still depends on the pressure generated, duct condition, Pitot tube position and suitability of the complete setup.

Compatible UNI-T Pitot Tube

The optional UNI-T Pitot tube for the UT366A has the following specifications:

Length: 350 mm
Diameter: 8 mm
Material: 304 stainless steel
Black silicone tube: one piece
White silicone tube: one piece
Silicone-tube length: 1 metre
Silicone-tube internal diameter: 5 mm
Silicone-tube external diameter: 9 mm

The Pitot tube is an optional accessory and should be confirmed separately when ordering the UT366A for airflow measurement.

Preparing for the Measurement

Before inserting the Pitot tube, check that:

The duct is operating under normal conditions
The test location is safe and accessible
The pressure hoses are correctly connected
The hoses are not folded, damaged or blocked
The Pitot tube is clean
The instrument displays a stable zero reading
The selected air-velocity unit is correct

Avoid taking measurements immediately after sharp bends, dampers, fans or other components that create highly turbulent airflow whenever a more stable test location is available.

Positioning the Pitot Tube

Insert the Pitot tube into the duct through a suitable access point. The front opening must face directly into the airflow.

Correct alignment is important. If the tube points away from the direction of airflow or is inserted at an angle, the measured velocity may be lower than the actual value.

During testing:

Keep the Pitot tube facing upstream
Hold it steady at each measurement point
Avoid contact with the duct wall
Allow the reading to stabilise
Record the measurement before moving to the next point

The HOLD function can help retain a reading when the display is difficult to view during insertion.

Do Not Rely on One Measurement Point

Air velocity is rarely identical across the entire duct. The centre may have a higher velocity, while areas near the duct wall may be slower.

For a more representative result, divide the duct into several measurement points and take readings across the duct area. The readings can then be averaged.

Using only the centre reading may overestimate the overall airflow, especially in large ducts or systems with uneven flow distribution.

Air Velocity and Air Volume Are Different

Air velocity indicates how fast the air is moving. Air volume indicates how much air passes through a duct over a specific period.

To estimate airflow volume, the technician needs:

Average air velocity
Internal duct dimensions
Duct cross-sectional area
Correct unit conversion

For a rectangular duct:

Air volume = Average air velocity × Duct width × Duct height

For a round duct, calculate the circular cross-sectional area before multiplying it by the average velocity.

Incorrect duct dimensions or using only one velocity reading can produce an inaccurate airflow-volume calculation.

Common Causes of Unstable Readings

A fluctuating air-velocity reading may be caused by:

Turbulent airflow
Incorrect Pitot tube alignment
Loose pressure hoses
Leaking or damaged hoses
Blocked pressure openings
Changing fan speed
Variable air volume controls
Testing too close to a bend or damper
Air leakage from the duct

Check the measurement setup before assuming the airflow system has a fault.

Where This Method Is Useful

The UT366A and Pitot tube combination is suitable for technicians checking:

AHU supply and return airflow
Factory ventilation systems
Kitchen and industrial exhaust systems
Data-centre cooling ducts
Laboratory ventilation
Building air-balancing work
HVAC testing and commissioning
Preventive maintenance

It can support contractors and facility teams working in Selangor, Kuala Lumpur, Johor, Penang and throughout Malaysia.

Is the UT366A Suitable for Your Application?

Choose the UT366A with a Pitot tube when the main requirement is to measure duct pressure and internal air velocity.

For quick checks at an air grille or open outlet, a vane or hot-wire anemometer may be easier to position. The correct instrument depends on the access point, air velocity, duct size and required measurement method.

For assistance selecting the appropriate airflow-testing instrument, contact MTM Precision with your duct size, application and preferred measurement unit.

MTM Precision Sdn Bhd

Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia

Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my