EngineerHub.orgWhat this simulator does
The model adds occupant-generated CO₂ and water vapour to the room while outdoor air dilutes both. It reports the overnight timeline, time above selected thresholds, the ventilation rate needed to meet a wake-up CO₂ target, and whether the calculated dew point exceeds a selected cold-surface temperature.
How to use this bedroom calculator
Enter length, width and ceiling height. A smaller room reaches higher CO₂ more quickly.
Enter adults, children and the expected sleep period. Use the default source rates unless you have better data.
Use ACH when you have an estimate, or enter measured outdoor airflow from a ventilation report or airflow reading.
Read wake-up CO₂ for ventilation and dew-point margin for moisture or condensation risk.
Do not know the ventilation rate? Start with the closest example bedroom, then compare the prediction with several nights of CO₂ and humidity monitor data.
Inputs
Example bedrooms
Room and occupancy
Ventilation
Humidity and condensation
Technical setting
Representative sleeping rates are editable because body size, age and metabolism matter.
CO₂ balance: dC/dt = G/V + (Q/V)(Cout − C)
Moisture balance: Mda dw/dt = Gw + ṁda(wout − w)
- Single, perfectly mixed room with constant airflow and occupancy.
- Bedroom temperature and outdoor conditions remain constant overnight.
- Moisture buffering by walls, bedding and furnishings is not modelled.
- If calculated air reaches saturation, excess moisture is reported as idealized condensation.
- CO₂ is used as a ventilation indicator; it is not a complete measure of indoor air quality.
Results
The long-term steady CO₂ level under these constant assumptions is approximately 2,090 ppm.
Overnight CO₂ and humidity timeline
CO₂ is plotted against the left axis and relative humidity against the right axis. Dashed lines show the user-selected reference values.
Scroll the plot horizontally for readable labels.
Worked example: two adults in a 30 m³ bedroom
Eight hours, 0.5 ACH, 20 °C, 45% starting RH and 5 °C outdoor air.
Wake-up CO₂ is about 2,060 ppm and wake-up RH about 55% under the constant-input model.
The model indicates that more outdoor air is needed for a 1,000 ppm wake-up target, while moisture may still remain acceptable.
Background
Engineering basis, assumptions, interpretation and practical limitations.
Place a calibrated CO₂ and humidity monitor away from the sleeper's face, windows, vents and radiators. Compare several nights.
Open or clear trickle vents, check transfer gaps and grilles, keep the bedroom door ajar where appropriate, or increase commissioned mechanical ventilation.
Window opening can rapidly increase ventilation, but actual airflow varies with wind and temperature. Consider security, noise, outdoor pollution and weather.
If humidity remains high despite acceptable CO₂, investigate wet laundry, damp construction, bathroom transfer, cold surfaces and inadequate whole-home extraction.
The default adult sleeping source rates are representative values derived from published residential modelling data. Children and adults vary with age, size and metabolism, so the advanced rates are intentionally editable.
- NISTIR 7212: representative sleeping CO₂ and water-vapour generation rates for adults and children.
- Persily & de Jonge, Carbon Dioxide Generation Rates for Building Occupants: occupant CO₂ generation and single-zone mass-balance context.
- EnergyPlus Psychrometric Services: humidity ratio, relative humidity and dew-point property relationships.
- ASHRAE Position Document on Indoor Carbon Dioxide: proper interpretation and limitations of indoor CO₂ measurements.
Frequently Asked Questions
Practical questions about assumptions, inputs, interpretation and limitations.
Use the target as a ventilation-planning reference, not a universal health limit. A lower target requires more outdoor air. Compare the result with local guidance and measured bedroom conditions.
People generate both CO₂ and moisture, but cold outdoor air can be dry when heated indoors. Ventilation may therefore be insufficient for CO₂ while humidity remains moderate.
Not reliably. Natural airflow changes with wind, temperature difference, opening size and building pressure. A monitor or measured airflow gives a better basis.
Place it in the occupied zone away from a sleeper's breath, windows, vents, radiators and direct sunlight. Compare several nights rather than one reading.
Typical particle filters and portable air cleaners do not remove meaningful CO₂. Outdoor-air ventilation is needed to dilute occupant-generated CO₂.
It means the predicted dew point is above the selected cold-surface temperature, so condensation is possible on that surface.