How many air movers do I need per square foot?

The S500 placement guidance commonly cited is one air mover per affected room, plus one per 50–70 SF of wet floor, plus one per 100–150 SF of wet wall above about two feet and ceiling, plus one for each wall inset or offset over 18 inches. The calculator gives the low and high count.

How do I size dehumidifiers for a water loss?

Divide the cubic footage by the IICRC chart factor for the class of water and dehumidifier type to get pints per day, then divide by the unit's AHAM rating. LGR factors are 100, 50, 40 and 40 for Classes 1–4; conventional are 100, 40, 30 and not rated for Class 4. Desiccants use air changes per hour instead.

Why do carriers cut drying to three days?

Three days is a common default, not a standard. The S500 dries to a goal, not a day count, and the daily psychrometric and moisture readings are the evidence for every day billed. The calculator prints the log to fill in.

Free tool · mitigation and adjusters

Air Mover & Dehumidifier Calculator

Equipment counts from the IICRC placement guidance and dehumidification chart, the cost per day, and a drying log that justifies every day on the invoice.

Affected roomsWall insets/offsets > 18 in

Wet floorSFWet wall above 2 ft + ceilingSF

Ceiling heightft

Class of water loss

Class 1 least water, slow evaporation · 2 whole room, wicking under 24 in · 3 overhead, walls wet above 24 in · 4 bound water in dense materials.

Dehumidifier type

Unit rating (AHAM)pints/day

DaysAir mover/day$Dehu/day$

Air movers

13–17

1 per room + 1 per 50–70 SF floor + 1 per 100–150 SF wall/ceiling + 1 per inset

Dehumidification needed

68 pints/day

3,360 cu ft ÷ 50 (Class 2, LGR)

Dehumidifiers

At 70 pints/day per unit, rounded up.

Equipment for 4 days

$2,900

17 air movers × $35 + 1 dehus × $130, per day. Days are justified by the log, not by a default.

Equipment justification and daily log

Drying log — equipment justification
Affected: 3 rooms, 420 SF wet floor, 260 SF wet wall/ceiling above 2 ft, 2 insets/offsets over 18 in.
Class 2 water. Volume 3,360 cu ft (8 ft ceilings).
Air movers: 13–17 (IICRC S500 placement guidance).
Dehumidification: 68 pints/day → 1 unit(s) at 70 pints/day each (3,360 cu ft ÷ 50 (Class 2, LGR)).

Day | Date | Outside temp/RH/GPP | Affected temp/RH/GPP | Dehu exhaust GPP | Moisture readings (location: reading / dry goal) | Equipment on site | Tech
1   |      |                     |                      |                  |                                                   | AM 17 / DH 1  |
2   |      |                     |                      |                  |                                                   | AM 17 / DH 1  |
3   |      |                     |                      |                  |                                                   | AM 17 / DH 1  |
4   |      |                     |                      |                  |                                                   | AM 17 / DH 1  |

Equipment stays until every reading meets its dry goal; the daily readings above are the basis for each day billed.

Factors from the IICRC initial dehumidification chart (rev. 3.1.22) and S500 air mover placement guidance. Confirm against the edition your carrier references.

Equipment the carrier will accept

Desk reviewers trim mitigation invoices in two places: the number of units and the number of days. The first is settled by showing the placement formula and the dehumidification math for the class of water. The second is settled only by daily readings that show the materials were not yet at their dry goal.

Climate changes the job. On the Gulf Coast (Houston, New Orleans, Tampa and Miami), outdoor air is too humid to use for drying, so the building is kept closed and the dehumidifiers do the work. Daily grain readings outside and inside show why. Frozen-pipe losses, like the February 2021 Texas freeze or a Chicago winter, often reach Class 3, with wet ceilings and wall cavities. That is where the cubic-foot sizing matters most.

Dehumidifier factors come from the IICRC “Initial Dehumidification Recommendation Factors and Formulas” chart (rev. 3.1.22). For the rest of a water claim, the supplement builder lists the rebuild lines that get cut and the proof each needs.

Questions

How many air movers do I need per square foot?: The S500 placement guidance commonly cited is one air mover per affected room, plus one per 50–70 SF of wet floor, plus one per 100–150 SF of wet wall above about two feet and ceiling, plus one for each wall inset or offset over 18 inches. The calculator gives the low and high count.
How do I size dehumidifiers for a water loss?: Divide the cubic footage by the IICRC chart factor for the class of water and dehumidifier type to get pints per day, then divide by the unit's AHAM rating. LGR factors are 100, 50, 40 and 40 for Classes 1–4; conventional are 100, 40, 30 and not rated for Class 4. Desiccants use air changes per hour instead.
Why do carriers cut drying to three days?: Three days is a common default, not a standard. The S500 dries to a goal, not a day count, and the daily psychrometric and moisture readings are the evidence for every day billed. The calculator prints the log to fill in.

Mitigation invoice getting cut?

Send the invoice and the drying log. We write the line-item mitigation and rebuild estimate with the equipment justification on it, free for the first one.

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