Predict the steady-state occupancy COâ‚‚ concentration from occupants and outdoor-air rate, or work back the outdoor-air rate needed for a target: checked against BB101 daily-average limits.
Tender-stage only. Verify final design to project spec and BB101 (2018).
For design guidance only. Always verify with a qualified engineer.
About this COâ‚‚ ventilation check calculator
This free COâ‚‚ ventilation check calculator predicts the steady-state carbon-dioxide concentration a space settles at from its occupancy and outdoor-air (fresh-air) rate. Or works backwards to the outdoor-air rate needed to hold a chosen target. And checks the result against the BB101 (2018) daily-average limits. It is built for UK ventilation designers, building-services engineers and M&E consultants sizing classroom and workplace ventilation at tender stage, or sanity-checking an existing space against indoor-air-quality guidance. Everything runs in your browser. Nothing is uploaded.
How steady-state COâ‚‚ is calculated
In predict mode the equilibrium concentration is C = Cout + (G ÷ Q) × 106, where G is the total COâ‚‚ generation (occupants × the per-person rate) in l/s, Q is the outdoor-air rate in l/s, and the 106 converts the volume fraction to ppm. Required mode inverts this to q = generation × 106 ÷ (target − outdoor) per person. Per-person generation rates come from Persily & de Jonge 2017 (ASHRAE 62.1 Appendix C) and CIBSE Journal CPD Module 142, a sedentary adult is about 0.0048 l/s. The verdict compares the equilibrium level to the BB101 daily-average limit (1000 ppm mechanical, 1500 ppm natural); the peak/maximum limits (1500 / 2000 ppm) are transient checks and are not modelled here.
Frequently asked questions
Which BB101 limit does the verdict use?
It compares the steady-state (daily-average) concentration against the BB101 daily-average limit, 1000 ppm for mechanical ventilation and 1500 ppm for natural. The higher peak limits (1500 / 2000 ppm) are transient checks that this steady-state model does not evaluate.
What COâ‚‚ generation rate should I enter?
Use the activity preset: sedentary adult 0.0048 l/s (CIBSE M142), office adult at 1.2 met 0.0052 l/s (ASHRAE 62.1), or child at 1.2 met 0.0029 l/s (Persily/de Jonge). Or enter your own. Selecting a preset fills the per-person generation field.
Does it model build-up over time or room volume?
No. This is a steady-state (equilibrium) model assuming full mixing, so it does not depend on room volume or simulate the transient rise and fall of COâ‚‚ through the day. Verify the final design to project spec and BB101 (2018) where a dynamic check is required.