Formula Used
- DryMass = WetMass / (1 + MCinitial/100)
- WaterToRemove = DryMass × (MCinitial − MCtarget)/100
- Psat(T) = 0.61078 × e^(17.2694T/(T+237.3)) (kPa)
- VPD = (1 − RH/100) × Psat(T) (kPa)
Hours = (WaterToRemove / Rate) × SafetyFactor
Days = Hours / OperatingHoursPerDay
How to Use This Calculator
- Select the material and the drying method you will apply.
- Enter wet mass and both moisture targets from your readings.
- Provide exposed area and thickness for the drying face.
- Set temperature, humidity, and air velocity for the work zone.
- Choose operating hours and a safety factor for uncertainty.
- Press Calculate to show results above the form.
- Use the CSV and PDF buttons to export the report.
Example Data Table
| Material | Initial MC (%) | Target MC (%) | Wet Mass (kg) | Area (m²) | Thickness (mm) | Temp (°C) | RH (%) | Air (m/s) | Method | Est. Days |
|---|---|---|---|---|---|---|---|---|---|---|
| Concrete | 12 | 6 | 1200 | 25 | 80 | 22 | 55 | 1.2 | Refrigerant Dehumidifier | ~8.40 |
| Wood | 18 | 10 | 450 | 18 | 35 | 28 | 45 | 2.0 | Heated Air | ~3.10 |
| Gypsum | 9 | 4 | 320 | 22 | 15 | 24 | 50 | 1.5 | Natural Ventilation | ~2.60 |
Moisture removal targets and field thresholds
Site drying decisions start with a measurable target moisture content aligned to coatings, flooring, insulation, or occupancy requirements. Contractors document baseline readings, then track reduction toward a defined limit with repeatable meter placement and timing. A practical workflow is to record three points per zone, average them, and flag outliers that suggest trapped water or blocked airflow.
Environmental conditions that control evaporation
Drying rate is strongly influenced by vapor pressure deficit, which increases when temperature rises or relative humidity falls. Moving from 60% to 40% relative humidity at the same temperature increases the driving potential by about one third. Dehumidification can hold stable humidity, while ventilation can stall when outdoor air is humid or when night cooling raises indoor humidity.
Air movement, boundary layers, and effective area
Air velocity reduces the stagnant boundary layer at the wet surface. Moderate air movement often delivers most of the benefit, while very high velocity brings diminishing returns and can increase dust. Effective area is equally critical: opening cavities, removing saturated finishes, and exposing both sides of a component can cut timelines sharply.
Thickness and material diffusion considerations
Thicker sections dry slower because moisture must migrate from deeper layers before it can evaporate. Dense materials like concrete and some masonry have longer diffusion paths and may require extended conditioning even when the surface feels dry. Recording thickness and exposure conditions supports realistic schedules and helps avoid premature installation that triggers adhesion loss, mold risk, or rework.
Capacity planning and documentation for crews
Once the estimated water to remove is known, capacity planning is straightforward: divide required removal by planned operating hours, then select equipment that meets that rate with a safety margin. Daily logs should capture temperature, humidity, method used, and moisture readings. Clear documentation improves coordination between trades and provides defensible evidence for closeout. When conditions change, update inputs and re-run estimates so crews can re-balance equipment, shifts, and protection measures without delaying critical downstream work unnecessarily.
FAQs
What moisture basis does this calculator use?
Moisture content is treated on a dry basis: water mass divided by dry solid mass, multiplied by 100. Use consistent readings and units across your project notes.
Why does humidity change drying time so much?
Lower relative humidity increases vapor pressure deficit, which increases evaporation potential. High humidity reduces that driving force, so the same airflow and temperature remove less moisture per hour.
How should I pick the safety factor?
Start at 1.10 to 1.25 for open surfaces with good access. Use 1.30 to 1.60 when cavities, coverings, or unknown wet pockets are likely. Increase it if readings vary widely across the zone.
Is the energy value a power bill estimate?
It is an approximate latent energy requirement based on water removed, plus a small overhead. Actual electrical use depends on equipment efficiency, heat losses, cycling, and control settings.
What if the material is insulation or layered assemblies?
If insulation is saturated, removal is often faster than drying in place. For layered assemblies, measure at multiple depths and model the exposed area realistically; hidden layers can extend drying even when surfaces appear dry.
How can I improve accuracy on site?
Measure temperature and humidity where drying occurs, not at a doorway. Re-check moisture at fixed locations daily. Update surface area after demolition or opening cavities, then rerun the calculator to keep the schedule aligned.