CO₂-Based Fresh Air Calculator
Outdoor air per person to hold a CO₂ target, from the steady-state mass balance.
Holding 1,000 ppm needs ~9 L/s per seated person — almost exactly ASHRAE 62.1's office rate. CO₂ sensors thus proxy ventilation per person, not air quality itself.
Formula
CO₂-Based Fresh Air Calculator is a free co2 ventilation for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About CO₂-Based Fresh Air Calculator
Outdoor air per person to hold a CO₂ target, from the steady-state mass balance. The calculation implements V_oa = G / (C_in − C_out) per person (ASHRAE 62.1 Appendix C — CO₂ mass balance). Holding 1,000 ppm needs ~9 L/s per seated person — almost exactly ASHRAE 62.1's office rate. CO₂ sensors thus proxy ventilation per person, not air quality itself.
How to use CO₂-Based Fresh Air Calculator
- 1Enter Occupants.
- 2Enter CO₂ per person in L/s (Seated office ≈ 0.0052; light activity 0.008).
- 3Enter Indoor CO₂ target in ppm.
- 4Enter Outdoor CO₂ in ppm.
- 5Read OA per person, Total outdoor air instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use CO₂-Based Fresh Air Calculator?
- ✓Implements the standard formula — V_oa = G / (C_in − C_out) per person
- ✓Reference cited on-page: ASHRAE 62.1 Appendix C — CO₂ mass balance
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the CO₂-Based Fresh Air Calculator use?+
It computes V_oa = G / (C_in − C_out) per person, per ASHRAE 62.1 Appendix C — CO₂ mass balance. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
Holding 1,000 ppm needs ~9 L/s per seated person — almost exactly ASHRAE 62.1's office rate. CO₂ sensors thus proxy ventilation per person, not air quality itself.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the CO₂-Based Fresh Air Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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