A documentation-based selection guide for parking-garage gas detection: compare gas coverage, model configuration, BMS interfaces and maintenance requirements before specifying equipment.
Parking garage gas detection has one job: keep exhaust fans ready for real vehicle exhaust, then let the BMS reduce fan runtime when the air is clean. The right sensor choice depends less on brand loyalty and more on fuel mix, code requirements, BMS integration, maintenance access, and how the garage is actually ventilated. For general CO exposure context, see BuildMEP’s carbon monoxide ppm safe levels guide.
This guide compares manufacturer documentation checked on 14 October 2026. It does not report a BuildMEP hands-on test, measured detection performance or a brand ranking. Confirm current order codes, installation manuals and project requirements before purchase.
Selection Starting Points
CO-Only or CO + NO2?
Choose gases from the adopted code, approved ventilation strategy and expected vehicle emissions. A petrol/gasoline fleet alone does not establish that CO-only control is permitted. For example, ICC’s explanation of 2024 IMC Section 404.1 describes CO detectors used with NO2 detectors for automatically operated enclosed-garage ventilation. This model-code example does not establish which edition or amendments apply to your site.
Add NO2 monitoring when the garage regularly sees diesel vehicles, delivery trucks, buses, service vans, loading activity, ambulance bays, generators, or mixed-fleet operation. NO2 is also increasingly part of code-based enclosed parking garage control language, so check the adopted code edition and local amendments early.
Product and Decision Table
| Product | Best Fit | Gas / Range | Outputs and Controls | Watch Before Specifying |
|---|---|---|---|---|
| Macurco CM-6 / CM-12 | CO-only retrofit or small garage fan control | CO display range listed as 0-200 ppm; manufacturer lists coverage up to 7,500 sq ft | Fan relay, alarm relay, buzzer, 4-20 mA | CO-only device. If NO2 is required, use a separate NO2 device or a dual-gas option. |
| Macurco CX-6 / CX-12 | Dual CO/NO2 monitoring with local control | CO and NO2; replaceable sensors; CX-6 listed to UL 2075 per manufacturer | Display, buzzer, fan relay, alarm relay, 4-20 mA | Confirm low-voltage vs line-voltage model and exact listing requirements with the submittal. |
| Honeywell E3Point | Networked BAS projects and multi-gas flexibility | Select the gas cartridge and range using the exact model datasheet; the linked sheet describes network variants | Linked network variants: BACnet MS/TP or Modbus; relay output. Standalone analog variants require their own datasheet | Confirm standalone, remote, or network model. Do not mix capabilities from different versions without checking the exact part number. |
| BAPI Digital CO/NO2 | Rough-service or duct applications with BAS communication | CO 0-500 ppm; NO2 0-20 ppm; approx. 7-year sensing elements per BAPI | Field-configurable BACnet MS/TP or Modbus RTU | Allow warm-up/commissioning time and confirm wall/beam vs duct configuration. |
| Conspec 911154-1 CO/VC | Purpose-built CO ventilation controller | CO 0-500 ppm; electrochemical sensor; listed sensor life expectancy 7 years | LCD, audible alarm, fan and alarm relays. Verify fault behavior and the complete fan-control circuit | CO-only. For diesel or code-driven NO2 requirements, pair with NO2 monitoring or use a dual-gas platform. |
| ACI CO-R | Analog CO input to BMS | CO 0-125 ppm default, 250 ppm max per ACI product page | 4-20 mA and 2-10 VDC output | No Modbus RTU compatibility per ACI. Best when the BMS provides the control logic. |
Sensor Coverage and Placement
Do not select sensor quantity from a universal area allowance. Develop a model-specific layout using installation instructions, airflow zones and approved project requirements. Manufacturer data may allow a different maximum coverage under listed conditions, and real garages have ramps, shafts, dead corners, jet fans, partitions, and traffic patterns that change the answer. For airflow-side coordination, BuildMEP’s duct sizing calculator can help with early ductwork checks.
- Start with manufacturer spacing and coverage instructions for the selected device.
- Add sensing where exhaust can collect: ramps, queuing lanes, payment areas, loading areas, low-airflow corners, and enclosed pockets.
- Zone sensors to match fan zones. A sensor on Level B2 should not always force every fan on every level to full speed.
- Mount in the occupied breathing zone unless the manufacturer or AHJ requires otherwise. Keep sensors away from direct tailpipe blasts, fan discharge, fresh-air openings, and washdown abuse.
- Coordinate access. A perfectly placed sensor that cannot be reached for bump testing and calibration will become a maintenance problem.
Sensor Layout Coordination Checklist
Garage area alone cannot determine sensor quantity. Record these inputs before asking the designer or manufacturer to prepare the layout:
- Adopted code edition, amendments and authority requirements.
- Garage plans, levels, ramps, partitions and likely vehicle emissions.
- Ventilation zones, airflow paths, queuing areas and stagnant pockets.
- Exact sensor model, gas channels, mounting instructions and coverage limits.
- Calibration access, power and communication routes, and fault-response requirements.
Count the points on the reviewed layout. An area-per-sensor calculation does not confirm coverage or compliance.
Setpoints and BMS Control
Setpoints are where garage articles often get too confident. A value like 25 ppm CO can be a common first-stage fan trigger in some manufacturer defaults and project sequences, but it should not be presented as a universal legal requirement. NO2 trigger values are also project- and jurisdiction-dependent.
For a real project, confirm four things: the adopted code, the AHJ’s expected alarm levels, the sensor manufacturer’s allowable setpoint range, and the owner’s required sequence of operation.
Example BMS Ventilation Sequence
This is an example only. Edit it to match the project code, AHJ comments, fan schedule, VFD minimum speed, smoke-control requirements, and manufacturer instructions.
- Under normal conditions, maintain the minimum ventilation required by the adopted code and approved sequence. Do not assume that a low gas reading permits fans to stop.
- If any CO sensor in a zone rises above the approved Stage 1 setpoint for the approved delay period, enable that zone’s exhaust fan and associated make-up air path.
- If CO continues to rise, or if NO2 reaches its approved ventilation setpoint, increase the fan to Stage 2 or ramp the VFD to the scheduled high speed.
- If the high alarm level is reached, command the zone fans to high speed, generate a BMS alarm, and activate any required local alarm device.
- If a sensor reports fault, loss of communication, end-of-life, or power failure, place the affected zone in the fail-safe ventilation mode required by the design.
- After gas concentration falls below the reset threshold for the approved purge time, return the zone to normal scheduled operation.
- Trend CO, NO2, fan status, fan speed, alarms, sensor faults, and manual overrides for commissioning and maintenance review.
Maintenance Notes
- Label every sensor by level, zone, and BMS point name.
- Keep calibration records available for inspection and troubleshooting.
- Follow the manufacturer’s bump test, calibration, and sensor replacement instructions.
- Replace sensing elements according to manufacturer service-life, test and end-of-life instructions; investigate faults and failed tests promptly.
- Test the full sequence, not only the sensor reading: sensor input, BMS alarm, fan start, VFD speed, damper response, and reset logic. For related control-signal thinking, see BuildMEP’s Siemens actuator replacement and BMS feedback guide.
Visual Guide
Before Specifying
For a project that permits CO-only monitoring, compare Macurco CM-6/CM-12 or ACI CO-R against the approved design and required interfaces. For garages with diesel exposure, uncertain vehicle mix, or newer enclosed-garage code requirements, start with CO + NO2 and coordinate the exact model, coverage, and sequence with the AHJ. The best design is not the one with the fanciest sensor; it is the one that is clear to commission, easy to maintain, and honest about how the fans will respond when exhaust levels rise. For more practical HVAC references, browse the BuildMEP HVAC guides.
