Restoration Equipment Sizing Calculator
Enter your drying chamber and loss details for an instant initial recommendation on air movers, dehumidifiers, and desiccant capacity — then send it to us and we'll stage the exact package.
The IICRC S500 air mover calculation is one air mover per affected room, plus one per 50–70 sq ft of wet floor, plus one per 100–150 sq ft of wet wall and ceiling above 2 ft, plus one per inset over 18". Dehumidifier PPD = cubic feet ÷ class factor. Restoration Equipment Supply’s calculator below does both instantly.
- Desiccant Dehumidifiers
- LGR Dehumidifiers
- Air Movers
- HEPA Air Scrubbers
- Portable Air Scrubbers
- Negative Air Machines
- HEPA Vacuums
- Generators
Your Initial Recommendation
Initial recommendation only. Final equipment quantity and placement depend on daily moisture readings, psychrometrics, grain depression, material moisture, temperature, vapor barriers, containment, and manufacturer specs. Water category affects safety, PPE, containment, and filtration — not equipment count. Based on IICRC S500 initial-recommendation factors.
Psychrometric & Air-Quality Tools
Check whether your dehumidifiers are actually pulling moisture (grain depression), read GPP and dew point, and size HEPA air scrubbers by air changes.
Readings & Verdict
How the IICRC S500 Math Works
These are the exact formulas this calculator runs — the same initial-recommendation factors published in the IICRC S500 standard for water damage restoration. Use them to check our numbers, or to fill out a drying log by hand.
What is the IICRC air mover calculation?
Air movers are counted from the wet surfaces, not the room volume. The calculator adds four parts and rounds up:
- Rooms1 air mover per affected room
- Wet floor1 per 50–70 sq ft (floor ÷ 70 low, ÷ 50 high)
- Walls & ceiling above 2 ft1 per 100–150 sq ft (÷ 150 low, ÷ 100 high)
- Insets & offsets1 per wall inset, closet or offset deeper than 18"
Low = rooms + floor ÷ 70 + walls ÷ 150 + insets. High = rooms + floor ÷ 50 + walls ÷ 100 + insets. The suggested starting count is the midpoint. Wall and ceiling area only counts above the 2-foot line, because wet drywall below 2 ft is usually covered by the floor air movers aimed at the wall base.
How many air movers per square foot?
For floors, plan one air mover per 50–70 square feet of wet flooring, plus one per room. A 600 sq ft wet floor in one room needs about 10–13 air movers before any walls are added. Wet walls and ceilings add one per 100–150 sq ft. Our standalone air mover calculator runs just this part.
What is the IICRC dehumidifier calculation?
Dehumidifiers are sized from the drying chamber’s volume. Required AHAM pints per day (PPD) = cubic feet ÷ class factor. Then number of units = required PPD ÷ your unit’s AHAM rating, rounded up. Desiccants use airflow instead: required CFM = cubic feet × air changes per hour ÷ 60.
| Water loss class | Conventional refrigerant | LGR | Desiccant (ACH) |
|---|---|---|---|
| Class 1 — least water | ft³ ÷ 100 | ft³ ÷ 100 | 1 ACH |
| Class 2 — carpet/pad, walls wet < 24" | ft³ ÷ 40 | ft³ ÷ 50 | 2 ACH |
| Class 3 — water from overhead | ft³ ÷ 30 | ft³ ÷ 40 | 3 ACH |
| Class 4 — specialty / bound water | Not recommended — use LGR or desiccant | ft³ ÷ 40 | 3 ACH |
Worked example: one Class 2 room vs. a Class 3 loss
| Input / result | Example A: 1 room, Class 2 | Example B: 3 rooms, Class 3 |
|---|---|---|
| Room size × rooms | 30 × 20 × 8 ft × 1 | 30 × 20 × 8 ft × 3 |
| Wet floor / walls+ceiling / insets | 600 / 400 sq ft / 2 | 1,800 / 1,500 sq ft / 4 |
| Air movers (low–high) | 15–19 → start with 17 | 43–58 → start with 51 |
| Chamber volume | 4,800 ft³ | 14,400 ft³ |
| LGR capacity needed | 4,800 ÷ 50 = 96 PPD → 1 LGR | 14,400 ÷ 40 = 360 PPD → 3 LGRs |
| Conventional refrigerant | 4,800 ÷ 40 = 120 PPD | 14,400 ÷ 30 = 480 PPD |
| Desiccant airflow | 4,800 × 2 ÷ 60 = 160 CFM | 14,400 × 3 ÷ 60 = 720 CFM |
Example B is where a single trailer-mounted 5,000 CFM desiccant dehumidifier starts to beat a stack of LGRs — one hookup, one unit to monitor, and drier process air at low temperatures.
How do you calculate grain depression?
Grain depression is the drop in moisture content between the air going into a dehumidifier and the air coming out. Grain depression = GPP of affected air − GPP of dehumidifier discharge, where GPP (grains per pound) is calculated from temperature and relative humidity. The psychrometric tool above does this for you: the default 80°F / 60% intake and 95°F / 25% discharge reads about 31 grains. As a working rule, our calculator flags anything under 20 grains as low — check for a clogged filter, a cold chamber, or an undersized unit.
What is the IICRC air mover calculation for a water loss?
Add 1 air mover per affected room, 1 per 50–70 sq ft of wet floor, 1 per 100–150 sq ft of wet wall and ceiling above 2 ft, and 1 per inset or offset over 18 inches. Round up. The low end uses the larger divisors (70 and 150); the high end uses 50 and 100.
What is the IICRC dehumidifier calculation?
Divide the chamber’s cubic feet by the class factor (LGR: 100, 50, 40, 40 for Classes 1–4; conventional refrigerant: 100, 40, 30 for Classes 1–3) to get required AHAM pints per day, then divide by your unit’s AHAM rating and round up.
How many air movers do I need for 1,000 square feet?
For 1,000 sq ft of wet floor in two rooms with 600 sq ft of wet wall, the IICRC math gives 21–28 air movers, about 25 to start. Floor-only, figure one per 50–70 sq ft plus one per room.
What is a good grain depression for a dehumidifier?
Higher is better. Our calculator treats 20 grains or more as a dehumidifier that is working; below that, check the filter, chamber temperature, and unit size. Track it daily in your drying log alongside material moisture readings.
Does water category change the equipment count?
No. Category 1, 2, or 3 water changes PPE, containment, cleaning and filtration — not the number of air movers or dehumidifiers. Class (how much material is wet) drives equipment.
Updated October 2026 · Reviewed by the Restoration Equipment Supply dispatch team
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How are air movers calculated?
We use the IICRC S500 air-mover worksheet. Low range = (rooms) + (wet floor ÷ 70) + (wet wall & ceiling above 2 ft ÷ 150) + (insets/offsets). High range swaps the divisors to ÷50 and ÷100. We round up and suggest the midpoint. Add one air mover per affected room and per wall inset or offset greater than 18 inches.
How is dehumidification sized?
First we compute chamber volume (length × width × height × rooms). Then Required AHAM PPD = volume ÷ a class factor. Conventional refrigerant factors are Class 1 = 100, Class 2 = 40, Class 3 = 30. LGR factors are Class 1 = 100, Class 2 = 50, Class 3 = 40, Class 4 = 40. Number of dehumidifiers = required PPD ÷ your unit's AHAM rating, rounded up.
How is desiccant capacity sized?
Desiccants are sized by air changes per hour (ACH). Required CFM = volume × ACH ÷ 60, where initial ACH is 1 (Class 1), 2 (Class 2), or 3 (Class 3 & 4). Number of units = required CFM ÷ the desiccant's process-air CFM (our trailer unit is 5,000 CFM). We always use process-air CFM, never reactivation or marketing airflow.
What do the water loss classes mean?
Class 1 — least amount of water, minimal absorption. Class 2 — significant water, wicking up walls under 24 inches. Class 3 — greatest amount, water from overhead, walls/ceilings saturated. Class 4 — specialty drying of low-permeance materials (hardwood, plaster, concrete). Higher class = more dehumidification and airflow.
How are electrical load and generator size estimated?
We estimate ~2.5 amps per air mover and ~9 amps per refrigerant/LGR dehumidifier for the drying package. Circuits = load ÷ usable amps (12A on a 15A circuit, 16A on a 20A circuit, at 80%). Generator size (kW) = running load × 120V ÷ 1000, plus 25% headroom. Trailer-mounted desiccants are powered separately (onboard or paired generator).
How is water volume and power cost estimated?
Water in the affected area (gallons) ≈ wet floor sq ft × standing-water depth (in) × 0.623. Estimated power cost = running kW × 24 hours × your electric rate × drying days. Both are planning estimates.
Is this a final drying plan?
No — it's an initial equipment recommendation. Final quantity and placement depend on daily moisture readings, psychrometrics, grain depression, material moisture content, temperature, vapor barriers, containment leakage, and manufacturer specs. Category of water affects safety, PPE, containment, and filtration — not equipment count. Our team confirms and fine-tunes before delivery.
Right-Sized the First Time
Under-size and the job stalls. Over-size and you overpay. Our calculator uses the same IICRC S500 factors the pros use — then our team fine-tunes it and delivers.
IICRC S500 Math
Air movers, LGR/refrigerant, and desiccant CFM sized by the industry-standard worksheet.
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How Our Equipment Calculator Works
Equipment calculator is sized to the job by our dispatch team, so you rent what the loss needs and nothing extra.
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