UNI-T UT366A Pressure Units Explained for HVAC Testing Malaysia
HVAC manuals, filter specifications and ventilation drawings do not always use the same pressure unit. One document may show kPa, while another uses mbar, mmH₂O or inH₂O.
The UNI-T UT366A Digital Manometer supports multiple pressure units, allowing technicians to display the measurement in the same unit used by the equipment specification.
Selecting the correct unit is essential before comparing or recording pressure results.
Pressure Units Supported by the UT366A
The UT366A supports:
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kPa
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mbar
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bar
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psi
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mmHg
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inH₂O
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inHg
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oz/in²
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kg/cm²
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ftH₂O
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mmH₂O
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hPa
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m/s and fpm for air-velocity measurement with a compatible Pitot tube
Its unit-memory function retains the selected unit for future use. Technicians should still confirm the displayed unit before every inspection.
What Is kPa?
kPa means kilopascal.
The pascal is an SI pressure unit, while one kilopascal equals 1,000 pascals.
The UT366A pressure range is:
0.00 to ±15.00 kPa
kPa is commonly used in:
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Industrial pressure specifications
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Fan data
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Mechanical systems
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General engineering documents
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Equipment manuals
Because many HVAC pressure differences are relatively small, readings may also be expressed in Pa, mbar or water-column units.
What Is mbar?
mbar means millibar.
The UT366A range is:
0.0 to ±150.0 mbar
The relationship between kPa and mbar is:
1 kPa = 10 mbar
For example:
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0.5 kPa = 5 mbar
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1.0 kPa = 10 mbar
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2.5 kPa = 25 mbar
mbar may appear in European equipment specifications, pressure instruments and ventilation documentation.
What Is hPa?
hPa means hectopascal.
The UT366A range is:
0.0 to ±150.0 hPa
The numerical relationship is:
1 hPa = 1 mbar
Therefore:
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10 hPa = 10 mbar
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50 hPa = 50 mbar
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100 hPa = 100 mbar
Although the numbers are equal, the unit should still be recorded clearly.
What Is mmH₂O?
mmH₂O means millimetres of water column.
The UT366A range is:
0 to ±1,531 mmH₂O
This unit is often used for:
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AHU filter pressure drop
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Duct static pressure
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Fan pressure
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Cleanroom pressure
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Exhaust systems
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Low-pressure ventilation checks
Approximate conversion:
1 kPa ≈ 101.97 mmH₂O
For example:
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0.1 kPa ≈ 10.20 mmH₂O
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0.5 kPa ≈ 50.99 mmH₂O
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1.0 kPa ≈ 101.97 mmH₂O
What Is inH₂O?
inH₂O means inches of water column.
The UT366A range is:
0.00 to ±60.29 inH₂O
This unit frequently appears in HVAC equipment, fan and filter specifications originating from the United States.
Approximate conversion:
1 kPa ≈ 4.015 inH₂O
For example:
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0.25 kPa ≈ 1.00 inH₂O
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0.5 kPa ≈ 2.01 inH₂O
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1.0 kPa ≈ 4.01 inH₂O
Before comparing results, check whether the specification uses inH₂O or another inch-based pressure unit.
What Is psi?
psi means pounds per square inch.
The UT366A range is:
0.000 to ±2.175 psi
Approximate conversion:
1 kPa ≈ 0.145 psi
psi is widely used for higher-pressure pneumatic, hydraulic and mechanical systems. However, many HVAC differential-pressure applications involve values small enough that water-column units may be easier to interpret.
What Are mmHg and inHg?
mmHg means millimetres of mercury.
The UT366A range is:
0.0 to ±112.5 mmHg
inHg means inches of mercury.
The UT366A range is:
0.000 to ±4.429 inHg
These units may appear in vacuum, atmospheric-pressure or older engineering references.
Approximate conversions include:
1 kPa ≈ 7.50 mmHg
1 kPa ≈ 0.295 inHg
Do not confuse inHg with inH₂O. They use different reference liquids and represent very different pressure values.
Quick Conversion Reference
| Pressure | Approximate equivalent |
|---|---|
| 1 kPa | 10 mbar |
| 1 kPa | 10 hPa |
| 1 kPa | 101.97 mmH₂O |
| 1 kPa | 4.015 inH₂O |
| 1 kPa | 7.50 mmHg |
| 1 kPa | 0.295 inHg |
| 1 kPa | 0.145 psi |
These conversions are approximate. For reporting or calibration work, use the required conversion convention and precision stated in the relevant procedure.
Which Unit Should You Select?
Select the same unit used by:
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The AHU manufacturer
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The filter specification
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The fan-performance document
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The project consultant
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The commissioning report
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The facility’s maintenance procedure
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The cleanroom or laboratory requirement
Avoid unnecessary conversion when the UT366A can display the required unit directly.
Example: AHU Filter Pressure Drop
If the filter manufacturer states the final pressure drop in Pa or mmH₂O, use the closest available UT366A display unit and ensure any required conversion is documented.
When monitoring filters:
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Use the same unit for every inspection
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Record the clean-filter baseline
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Record the current reading
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Note the fan operating condition
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Compare with the manufacturer’s limit
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Do not replace the filter based only on appearance
Changing units between inspections can cause confusion even when the actual pressure has not changed.
Example: Fan Pressure
A fan specification may list pressure in Pa, kPa or inH₂O.
Before comparing the UT366A reading:
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Confirm whether the specification refers to static, velocity or total pressure.
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Select the correct UT366A unit.
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Use the approved pressure-test points.
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Record the P1 and P2 connection arrangement.
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Confirm the fan speed and damper position.
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Compare readings under similar operating conditions.
The correct unit alone does not make the test valid if the measurement method is different.
Common Unit Mistakes
Incorrect conclusions may result from:
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Comparing kPa directly with Pa
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Confusing mbar with bar
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Confusing inH₂O with inHg
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Ignoring a decimal point
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Recording a value without its unit
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Changing units between inspections
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Comparing gauge pressure with differential pressure
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Using rounded conversions for a critical acceptance test
Always record the value and unit together.
Get Help Selecting the Correct Pressure Unit
For assistance using the UNI-T UT366A for filter, fan, duct or room-pressure measurement, WhatsApp MTM Precision with a photo of the equipment specification and the required pressure 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
30 Sep 2026
