Structural Drying Equipment Sizing Calculator
Calculate the number of air movers and dehumidifiers required for structural drying jobs based on IICRC S500 standards. Enter the affected area dimensions and conditions to get equipment recommendations.
Formulas Used
Total Affected Surface Area:
Atotal = (L × W) + (Nwalls × Hwall × Lwall) + Aceiling
Air Movers (IICRC S500):
Nmovers = ⌈ Atotal / Sclass × Fcat × Fclass4 ⌉
where Sclass = 16 (Class 1), 12 (Class 2), 10 (Class 3 & 4) sq ft/mover
Fcat = 1.25 for Category 3; Fclass4 = 1.20 for Class 4
Dehumidifiers — Volume Method:
Ndehum = ⌈ Vroom / Cclass × FRH × Fcat ⌉
where Cclass = 1,600 / 1,200 / 1,000 / 800 cu ft per unit (Class 1–4)
FRH = 1.15 if RH > 80%
Moisture Load (Psychrometric):
Psat = e(20.386 − 5132/TR) (inHg, Antoine equation)
W = 7000 × 0.622 × Pv / (Patm − Pv) (grains/lb dry air)
Moisture Load = ρair × V × ΔW / 7000 × ACH × 24 hr × 2 pt/lb
Dehumidifiers — Capacity Method:
Ndehum = ⌈ Moisture Load (pt/day) / 150 pt/day ⌉
Final Dehumidifier Count:
Nfinal = max(Nvolume method, Ncapacity method)
Air Scrubbers:
Nscrubbers = ⌈ Vroom / 2,000 ⌉ (Cat 2) or ⌈ Vroom / 1,500 ⌉ (Cat 3)
Assumptions & References
- Based on IICRC S500 Standard for Professional Water Damage Restoration (current edition).
- Air mover density: 1 per 10–16 sq ft of affected surface area depending on water class.
- LGR dehumidifier rated capacity: 150 pints/day at AHAM conditions (80°F, 60% RH).
- Psychrometric calculations use a simplified Antoine equation for saturation vapor pressure; sea-level atmospheric pressure (29.92 inHg) assumed.
- Air density approximated at 0.075 lb/cu ft adjusted for temperature; 3 air changes per hour assumed for moisture load calculation.
- Drying time estimates are general guidelines; actual drying time depends on material type, building construction, and daily monitoring of moisture readings.
- Category 3 water damage requires additional safety protocols; consult a certified restorer (WRT/ASD credential) before proceeding.
- Class 4 drying (hardwood, concrete, plaster) may require specialty equipment such as desiccant dehumidifiers or injectidry systems not captured here.
- Air scrubbers should use HEPA filtration for Category 2 and 3 jobs; negative air pressure recommended for Category 3.
- This calculator provides estimates only. Always verify with on-site moisture readings and professional judgment.