UNI-T UT366A for Boiler and Furnace Draft Pressure Testing Malaysia

Boilers and industrial furnaces depend on controlled airflow and flue-gas movement for safe and efficient operation. Draft pressure that is too high, too low or unstable may indicate problems involving the chimney, induced-draft fan, forced-draft fan, damper or flue path.

The UNI-T UT366A Digital Manometer can measure positive, negative and differential pressure within its specified range. It may support draft-pressure checks when used with appropriate connection accessories and a safe measurement procedure.

What Is Draft Pressure?

Draft pressure is the pressure difference that moves combustion air and flue gas through a boiler, furnace or exhaust system.

A system may use:

Natural chimney draft
Forced-draft fan
Induced-draft fan
Balanced-draft arrangement
Mechanical exhaust system

Many furnace and flue sections operate below the surrounding atmospheric pressure. A negative reading may therefore be normal.

The required pressure depends on the equipment design and operating load. Always compare measurements with the manufacturer’s specification or approved commissioning data.

Where Draft Pressure May Be Checked

Depending on the system design, pressure points may include:

Combustion-air inlet
Burner wind box
Furnace chamber
Before or after a heat-exchange section
Before or after a dust collector
Induced-draft fan inlet
Induced-draft fan outlet
Flue duct
Chimney connection
Across an air filter

Use only approved pressure-test points. Do not drill, open or modify operating combustion equipment without proper authorisation and a safe-work procedure.

Why Use the UT366A?

The UT366A provides:

Positive-pressure measurement
Negative-pressure measurement
Differential-pressure measurement
Independent P1 and P2 readings
Green positive-pressure indication
Red negative-pressure indication
MAX, MIN, AVG and HOLD functions
Multiple selectable pressure units
Backlit display
Magnetic hook for convenient positioning

Its pressure measurement range is ±15.00 kPa, with a specified accuracy of ±0.5% full scale at 25°C.

Important Temperature Limitation

The UT366A’s stated operating-temperature range is 0°C to 50°C.

Do not connect the instrument directly to hot flue gas, steam, liquid, corrosive gas or contaminated process material.

A suitable measurement arrangement may require:

Heat-resistant pressure tubing
A cooling section
A condensate trap
A filter
An isolation component
Other accessories specified by the equipment manufacturer

The complete setup must prevent hot gas, moisture, soot or chemicals from entering the UT366A pressure ports.

Measuring Negative Furnace Pressure

A furnace chamber may be maintained under slight negative pressure to reduce the risk of hot gas escaping through openings.

To check the pressure:

Confirm the approved test point.
Verify that the expected pressure is within the UT366A range.
Install the required protective connection arrangement.
Connect the pressure hose securely.
Confirm the correct reference point.
Select the required pressure unit.
Start measurement from a safe position.
Allow the reading to stabilise.
Record the value, sign and operating load.

Do not place personnel directly in front of inspection doors or openings during operation.

Checking Pressure Across a Component

Differential-pressure measurement can be used to compare pressure before and after an accessible system component.

Possible examples include:

Combustion-air filter
Dust-collection section
Heat-exchange section
Damper
Fan
Flue restriction point

Connect P1 and P2 according to the required pressure direction.

If the value appears with the opposite sign, check whether the hoses have been reversed. Record the exact P1 and P2 connection points for repeatability.

Signs of Excessive Negative Draft

A stronger-than-expected negative pressure may be related to:

Excessive induced-draft fan speed
Damper opened too far
Incorrect control setting
Reduced resistance in the flue path
System imbalance
Operating-load change
Incorrect pressure reference
Reversed connections

Do not adjust the fan or damper based on one reading alone. Confirm the operating specification and combustion condition first.

Signs of Weak or Lost Draft

A pressure value closer to zero than expected may indicate:

Blocked flue
Dirty heat-transfer surface
Closed or restricted damper
Induced-draft fan problem
Belt or impeller issue
Air leakage
Blocked pressure-test point
Leaking measurement hose
Condensate inside the pressure line
Chimney or exhaust restriction

Because these conditions may create combustion and safety risks, boiler or furnace adjustments should be performed only by competent personnel.

Why the Reading May Fluctuate

Draft pressure can change due to:

Burner cycling
Changing fuel input
Variable fan speed
Damper movement
Pulsating combustion
Wind affecting the chimney
Door or inspection-port movement
Unstable process load
Moisture in the pressure line
Turbulence at the test point

The UT366A’s MAX, MIN and AVG functions can help document variations, but significant fluctuations still require investigation.

Check the Hose and Pressure Line

Before diagnosing the combustion system, inspect the measurement line for:

Leakage
Cracks
Loose fittings
Heat damage
Internal blockage
Soot accumulation
Condensation
Incorrect hose material
Kinks
Contact with hot surfaces

A damaged or blocked line can produce a false pressure reading.

Select the Correct Pressure Unit

The UT366A supports units including:

kPa
mbar
bar
psi
mmHg
inH₂O
inHg
mmH₂O
ftH₂O
hPa

Boiler and furnace documentation may use mbar, mmH₂O, inH₂O or another unit.

Select the same unit used in the manufacturer’s specification whenever possible. Always record the pressure value together with its unit and sign.

Record the Operating Condition

A useful draft-pressure record should include:

Equipment identification
Measurement location
P1 and P2 connection points
Pressure unit
Positive or negative sign
Burner operating stage
Fan speed
Damper position
Fuel or process load
Measured value
Maximum and minimum values
Abnormal symptoms
Action taken

A reading taken at low load should not be compared directly with a full-load value unless the equipment procedure allows it.

Pressure Measurement Is Not Combustion Analysis

The UT366A measures pressure and optional duct air velocity. It does not measure:

Oxygen
Carbon monoxide
Carbon dioxide
Flue-gas temperature
Combustion efficiency
Fuel-air ratio
Smoke or soot level

A complete boiler or furnace assessment may require a suitable combustion analyser, temperature instrument and other safety equipment.

Safety Considerations

Before performing draft-pressure testing:

Follow the site’s permit and safety procedure
Confirm the expected pressure and temperature
Use approved test points
Wear the required personal protective equipment
Keep hoses away from hot and moving parts
Do not expose the UT366A to flue gas directly
Stop testing if hot gas, flame, liquid or soot enters the pressure line
Have combustion-system adjustments performed by authorised personnel

Never use the instrument in an application that exceeds its stated pressure or environmental limits.

Enquire About Draft-Pressure Measurement

For assistance selecting the UNI-T UT366A for boiler, furnace, flue or ventilation pressure measurement, WhatsApp MTM Precision with the expected pressure range, temperature and photos of the approved 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