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Balo Meters & HVAC Capture Hoods: Accurate Volumetric Airflow Balancers for Ventilation Audits

Quick Answer: Balo meters and HVAC capture hoods measure air volume at diffusers and grilles during ventilation audits. Silver Instruments supplies inline thermal mass flow meters for duct airflow verification where capture hood readings need cross-checking or permanent monitoring. Send duct size in mm, airflow range in m3/h, and output signal to get a quote.

What Balo Meters Do in Ventilation Audits

Balo meters are portable capture hoods with a fabric canopy. A technician places the canopy over a ceiling diffuser or grille. The base unit records air velocity and calculates volumetric flow in m3/h or CFM. Most models read from 40 to 4000 m3/h. Accuracy is typically plus or minus 3 percent of reading plus 7 m3/h at standard conditions. This is enough for many ventilation audits. But outdoor air temperature, back pressure from the hood, and diffuser type can shift the reading. Many commissioning teams cross-check at least one duct traverse with an inline air flow meter.

Why Capture Hood Readings Need Inline Verification

This is the part most engineers skip. A capture hood creates a small back pressure at the diffuser. That back pressure changes the air flow path. On low pressure duct systems the error can be significant. In practice we have seen readings differ by 5 to 8 percent between a capture hood and an inline duct meter. For a hospital in Singapore that difference matters. Under-ventilation can fail ASHRAE 170 or local code. Over-ventilation wastes fan energy. An inline thermal mass flow meter gives a direct mass flow reading in kg/h or normalized m3/h. It is not affected by diffuser geometry.

Silver Instruments Thermal Mass Flow Meter for Duct Air

Silver Instruments builds inline thermal mass flow meters for air and inert gas. The SI-TMF series covers duct sizes from DN25 to DN300 with insertion or inline styles. A typical SI-TMF-100 inline meter on a DN150 duct reads 5 to 1000 m3/h. Output is 4-20 mA HART plus RS485 Modbus. Accuracy is plus or minus 1.5 percent of reading plus 0.5 percent full scale. Response time is under 0.5 seconds. The sensor works from minus 20 to 120 degrees Celsius and up to 10 bar for compressed air lines. For paint or solvent exhaust, an ATEX Zone 1 rated sensor body is available. This covers most HVAC, cleanroom, and exhaust air audits. For a DN100 duct carrying 300 m3/h, the SI-TMF-100 insertion meter is a direct fit. For a DN250 duct carrying 3500 m3/h, the SI-TMF-200 inline meter gives a stable 4-20 mA HART signal.

Where Balo Meters Fit in a Ventilation Audit Workflow

A standard ventilation audit is not just reading ducts. Technicians list all diffusers, pitot traverse the main duct, and compare design airflow. Balo meters speed up the diffuser counts. Inline meters from Silver Instruments verify the main branch and provide a logging reference. A commissioning contractor in Jakarta recently used a Balo style capture hood for 120 diffusers in a 20 floor office tower. They also installed two SI-TMF inline meters on the main AHU supply and return ducts. The inline data caught a 12 percent under-supply on the 14th floor. The capture hood alone missed it because the diffuser layout changed during fit out. That is a real situation. It is common in retrofit buildings. A paint manufacturer in Southeast Asia installed an SI-TMF inline meter on a solvent exhaust duct after a capture hood audit passed the system. The inline meter found a 10 percent drop in flow within three weeks because the filter cartridges loaded. This sort of drift matters for VOC exposure.

Ordering Data You Need to Send

Send us your duct size in mm, airflow range in m3/h or kg/h, air temperature, duct static pressure, and output signal. Include whether you need a hand held or fixed meter. For Balo meters we can direct you to a loc