WELL and RESET
WELL v2 and RESET Air specify exactly how accurately a CO2 sensor must measure, how often it must report, and how many devices are required per area. The EnoSense® CO2 meets these requirements—even at its maximum values, not just typical ones.
From the Request to the Room
Step 1 of 6First, the scope: WELL v2 governs CO2 measurement in Feature A08, while RESET Air governs it through Equipment Classes A through C. Class B applies to a building’s permanent fixtures. Both specify numerical values, not intentions.
What the Two Standards Require
RequirementWELL v2 and RESET Air are the two sets of guidelines that not only recommend indoor air quality measurements but also specify measurable requirements: accuracy, resolution, reporting frequency, installation location, and device density. Anyone issuing a bid for a certified building must be familiar with these figures—and even those who aren’t will still find them to be the most useful benchmark.
WELL v2 regulates CO2 measurement in Feature A08, “Air Quality Monitoring and Awareness.” It requires an accuracy of 10 percent at 750 ppm, a reading at least every ten minutes, and one sensor per 3,500 square feet—or approximately 325 square meters.
RESET Air follows the device-based approach: The standard for accredited measuring devices divides them into Classes A, B, and C, and only Classes A and B are approved for use in projects. Class B is the class for permanent installation in buildings—it requires an accuracy of 50 ppm and 3 percent of the measured value for CO₂, a resolution of 5 ppm, a measurement range of 400 to 5,000 ppm, and data output at least every five minutes.
| Size | WELL v2, Feature A08 | RESET Air, Class B |
|---|---|---|
| CO2 Accuracy | 10 percent at 750 ppm | 50 ppm and 3 percent of the measured value (400 to 2,000 ppm) |
| Resolution | Not specified | 5 ppm |
| Measurement range | Not regulated | 400 to 5,000 ppm |
| Polling Interval | No more than 10 minutes | at least every 5 minutes |
| Temperature | Not part of A08 | Range 0 to 40 °C, accuracy 1 K |
| Humidity | Not part of A08 | Range: 10 to 80 percent, accuracy: 8 percent |
| Installation | 1.1 to 1.7 m, at least 1 m from doors, windows, and air vents | 0.9 to 1.8 m, against the wall, at least 5 m from windows and air inlets |
| Density | one unit per 325 m² | one unit per room type, up to 500 m² |
The Proof, Line by Line
EnoSense® CO2The following table compares the specified requirement with the value from the data sheet. The comparison is not made with the typical value, but with the maximum value —that is, with the worst-case guaranteed measurement. Even under these conditions, the sensor remains below both limits.
The key factor is accuracy. The EnoSense® CO2 typically has an accuracy of ± (30 ppm + 3 percent of the measured value), with a maximum of ± (45 ppm + 3 percent). At 750 ppm, this typically amounts to 52.5 ppm and a maximum of 67.5 ppm, or 7.0 and 9.0 percent. WELL allows 10 percent. RESET Class B allows 50 ppm plus 3 percent—the sensor remains below this limit at 45 ppm.
| Requirement | Required | EnoSense® CO2 | Meets |
|---|---|---|---|
| WELL: CO2 Accuracy | 10% at 750 ppm | 9.0% (max.), 7.0% (typical) | ✓ |
| WELL: Reporting interval | no more than 10 minutes | every 5 minutes | ✓ |
| RESET B: CO2 Accuracy | 50 ppm + 3% | 45 ppm + 3% (max.) | ✓ |
| RESET B: Resolution | 5 ppm | 1 ppm | ✓ |
| RESET B: Measurement Range | 400 to 5,000 ppm | 0 to 10,000 ppm | ✓ |
| RESET B: Data Output | every 5 minutes | every 5 minutes | ✓ |
| RESET B: Temperature | 0 to 40 °C, ± 1 K, 0.1 K resolution | 0 to 80 °C, ± 0.4 K (max.), 0.1 K | ✓ |
| RESET B: Humidity | 10 to 80%, ±8%, 1% resolution | 0 to 99%, ± 3.5% (max.), 0.5% | ✓ |
| RESET B: Operating range | 0 to 40 °C, 10 to 85 % rF | 0 to 50 °C, 0 to 99% relative humidity, non-condensing | ✓ |
| RESET B: Fixed Mounting | Option required | Wall mount included | ✓ |
Where the Line Is Drawn
Calculated honestlyA sensor alone does not make a building certified, and we do not claim that it does. Three factors are part of the truth.
WELL A08 requires three out of seven parameters. The list includes particulate matter, CO2, carbon monoxide, ozone, nitrogen dioxide, VOCs, and formaldehyde. Of these, our devices measure CO2. They also measure temperature and humidity, but those are not on this list—they are accounted for elsewhere in WELL, under Feature T06 for thermal comfort, and there, the EnoSense® CO2 also meets the requirements for density, installation, and measurement frequency.
RESET Air additionally requires PM2.5 and TVOC —particulate matter and total volatile organic compounds. Our devices do not measure these. For a RESET project, they are therefore required separately, while the EnoSense® CO2 covers the CO2, temperature, and humidity aspects.
Formal accreditation is a separate process. RESET tests devices using its own procedure and then lists them accordingly. What is shown here is a comparison of the data sheet values with the published Class B requirements—not an existing accreditation. If your project requires accreditation, please contact us before issuing a request for proposals.
What the Standards Require Beyond the Sensor
Project PerspectiveNeither standard stops at the measuring device. Two requirements can add to planning costs if they’re not identified early on—and we meet both of them with devices from the same product line.
What this means for your request for proposals
9 points- Specify the standard against which the test is conducted: WELL v2 Feature A08 or RESET Air Class B—the numbers differ.
- Specify accuracy as a formula, not as a percentage: ± (ppm + percentage of the measured value); otherwise, the specification is not comparable for high values.
- Specify resolution and measurement range separately: 5 ppm and 400 to 5,000 ppm are the minimum requirements for RESET Class B.
- Specify the reporting interval: no more than 10 minutes according to WELL, no more than 5 minutes according to RESET Class B.
- Specify the installation height as 1.1 to 1.7 m if WELL applies.
- Specify device density: one device per 325 m² or per usage zone.
- List the in-room display as a separate item, one per 325 m².
- List annual functional testing and calibration as a maintenance service.
- Provide a second device for particle and VOC measurement: our sensors do not measure these.
Information current as of September 16, 2026. Regulatory information has been compiled to the best of our knowledge and does not constitute legal advice. The text of the currently applicable version is always authoritative.
- WELL v2, Feature A08 “Air Quality Monitoring and Awareness,” Parts A08.1 and A08.2, Q4 2021 Version: Accuracy, Reporting Frequency, Installation, Density, and Display.
- WELL v2, Feature T06 “Thermal Comfort Monitoring,” Part T06.1, Version Q4 2021: Temperature and humidity, one sensor per 3,500 square feet, measurements at least every 15 minutes.
- RESET™ Air Standard for Accredited Monitors v2.0 dated September 21, 2018, Section 2.6.2 (Basic Requirements and Data Output), 2.6.5 (CO₂), 2.6.6 (Temperature), and 2.6.7 (Humidity).
- RESET™ Air Standard for Commercial Interiors v2.0 dated January 31, 2018, Sections 2.2.6 (Installation) and 2.2.7 (Number of Units, Coverage Area 500 m²).
- Device specifications from the product data sheet AL-439-00-868 EnoSense® CO2, Version 08 dated August 1, 2025.
Would you like us to run the numbers for your building?
Send us the floor plan, dimensions, and target system. You’ll receive a recommendation for the number of units, a list of part numbers, and a quote.