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Ventilation Air Change Calculator
Convert measured airflow and outside-air fraction into room air changes and ideal mixing time.
Room length (m), Room width (m), Room height (m), Measured total airflow (m³/h), Outdoor-air share (%), Target ideal replacement (%)
JSON
Browser only
Runs locally in your browser. Your files, pasted content and generated output are not uploaded. Reset clears this tool’s working data.
This tool needs JavaScript. If it does not load, refresh the page and try again.
How to use this tool
- Enter the labelled values using the displayed units and explicit assumptions.
- Choose Calculate result and review the complete report and any undefined or no-solution states.
- Choose Download result to save the complete JSON. Reset clears the result and restores example controls.
Examples
Room length (m): 5
Room width (m): 4
Room height (m): 2.5
Measured total airflow (m³/h): 300
Outdoor-air share (%): 50
Target ideal replacement (%): 95
Limitations
- Positive rectangular room dimensions m;nonnegative total airflow m³/h,outside-air fraction0–100%,target replacement0–<100%. Report total/outdoor ACH and perfect-mixing time=-ln(1-fraction)/outdoorACH;zero outdoor flow gives null time except zero target. No required rate,health protection,contaminant removal or measured mixing guarantee. Maximum admitted target replacement99.999999999%.
- Scalar controls accept explicit finite decimal syntax;positive values normally1e-12–1e12,nonnegative0–1e12 unless a narrower range is stated. JSON numeric rows use finite IEEE754 values within their stated bounds. Derived counts above1billion and nonfinite results refuse. Combined input<=400000UTF8 bytes;complete JSON<=4MiB. All processing stays in your browser.
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