How to Check Fan Inlet and Outlet Pressure with UNI-T UT366A Malaysia

A ventilation fan may continue running even when airflow performance has changed. Dirty filters, blocked ducts, incorrect damper positions and fan problems can all affect pressure across the system.

The UNI-T UT366A Digital Manometer allows HVAC and factory-maintenance technicians to measure pressure at the fan inlet and outlet or compare both points using differential-pressure mode.

Why Measure Fan Pressure?

Pressure measurements can help technicians determine whether a fan and its connected duct system are operating consistently.

Fan-pressure checks may support investigations involving:

Low airflow
Weak extraction
Uneven ventilation
Excessive filter restriction
Blocked ducts
Incorrect damper settings
Fan-speed changes
Unexpected noise
Process exhaust problems
Changes after maintenance work

Pressure readings should be assessed together with airflow, vibration, motor condition and the fan manufacturer’s performance information.

Understanding Fan Inlet Pressure

The inlet or suction side of a fan commonly operates below the surrounding atmospheric pressure.

A negative-pressure reading at the inlet may therefore be normal.

Unexpected inlet-pressure changes may be related to:

Dirty inlet filter
Blocked intake
Closed or partially closed damper
Collapsed flexible duct
Excessive duct resistance
Obstruction before the fan
Incorrect fan speed
Change in system configuration

The technician should compare the reading with an earlier baseline taken under the same operating condition.

Understanding Fan Outlet Pressure

The discharge side of a fan generally produces pressure to move air through the downstream duct system.

A low outlet-pressure reading may be associated with:

Reduced fan speed
Incorrect rotation
Damaged impeller
Loose belt
Air leakage
Open bypass
Incorrect damper position
Fan-performance deterioration

A high outlet pressure does not automatically mean good airflow. It may also occur when the downstream duct is restricted or a damper is closed.

Measuring Inlet Pressure

For inlet-pressure measurement:

Locate the approved pressure-test point before the fan.
Connect the pressure hose securely.
Ensure the reference port is exposed according to the required gauge-pressure setup.
Select the required pressure unit.
Start the fan and allow operation to stabilise.
Record the pressure value and sign.
Note the fan speed, damper position and filter condition.

Do not place an open reference hose where direct airflow or wind can affect the reading.

Measuring Outlet Pressure

For outlet-pressure measurement:

Locate a suitable static-pressure point after the fan.
Avoid using a test point directly in highly turbulent discharge airflow.
Connect the pressure hose securely.
Confirm the selected measurement unit.
Allow the fan to operate steadily.
Record the value.
Compare it with the normal baseline or approved equipment data.

Use the same test point for future inspections whenever possible.

Measuring Pressure Across the Fan

The UT366A’s P1 and P2 ports can compare pressure between the fan inlet and outlet.

A typical setup involves:

One hose connected to the inlet-pressure point
One hose connected to the outlet-pressure point
The UT366A set to differential-pressure mode
The system operating at its normal fan speed

If the displayed sign is opposite to what is expected, check whether the P1 and P2 connections have been reversed.

Record the exact hose arrangement so future measurements can be repeated consistently.

Why One Reading Is Not Enough

A single pressure reading cannot confirm the complete condition of a fan.

Technicians should also consider:

Air velocity
Calculated air volume
Motor current
Fan speed
Belt condition
Bearing vibration
Mechanical noise
Filter condition
Damper position
Duct leakage
Equipment load

For example, a fan may show increased pressure because a downstream damper is closed, while the actual airflow has decreased.

Establish a Baseline

After installation, commissioning or major maintenance, record normal fan-pressure values.

A useful baseline should include:

Fan identification
Measurement date
Inlet pressure
Outlet pressure
Differential pressure
Pressure unit
Fan speed
Damper position
Filter condition
Motor operating condition
Airflow or air-volume reading, if available

Future measurements can then be compared with this reference.

Common Causes of Incorrect Readings

Fan-pressure results may be unreliable when:

Pressure hoses are leaking
P1 and P2 are reversed
The hose is kinked
Moisture is trapped inside the hose
The test point is blocked
The measurement point is too close to a bend
The fan speed changes during the test
An access panel is open
The selected pressure unit is incorrect
The open reference is exposed to direct airflow

Inspect the setup and repeat the measurement before diagnosing a fan fault.

Using the MAX, MIN and AVG Functions

Fan pressure may vary during operation.

The UT366A provides:

MAX to capture the highest reading
MIN to capture the lowest reading
AVG to view an average value
HOLD to retain the displayed result

These functions can help when the display is difficult to observe or when the pressure varies slightly during the test.

Large fluctuations should still be investigated rather than hidden by an average reading.

Pressure Range and Units

The UT366A has a pressure range of ±15.00 kPa and a specified accuracy of ±0.5% full scale at 25°C.

Available units include:

kPa
mbar
bar
psi
mmHg
inH₂O
inHg
mmH₂O
ftH₂O
hPa

Always compare results using the same unit stated in the fan or ventilation-system documentation.

Suitable Applications

Fan-pressure testing with the UT366A can support:

Factory ventilation systems
HVAC air-handling units
Exhaust fans
Dust-collection systems
Kitchen exhaust systems
Cooling-air systems
Process ventilation
Laboratory extraction
Data-centre cooling
Building supply and return systems

It is suitable for maintenance teams and contractors working across Selangor, Kuala Lumpur, Johor, Penang and Malaysia.

Select the Correct Fan Testing Instruments

The UT366A measures fan-system pressure. A complete fan assessment may also require an anemometer, tachometer, clamp meter or vibration meter.

For assistance selecting the appropriate instruments, WhatsApp MTM Precision with the fan type, expected pressure range and photos of the available test points.

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