What is GPP in water damage restoration?

GPP stands for Grains Per Pound, measuring the specific weight of water vapor in dry air (1 lb = 7,000 grains). In water damage restoration, tracking GPP across affected rooms, unaffected areas, and dehumidifier exhaust proves drying progress.

What is grain depression?

Grain depression is the difference between ambient room GPP and dehumidifier exhaust GPP. An LGR dehumidifier should achieve at least 15–20 GPP depression during active drying.

FREE FIELD TOOL IICRC S500 PSYCHROMETRICS

Psychrometric GPP & Dew Point
Calculator

Calculate Grains Per Pound (GPP), Dew Point (°F), Vapor Pressure, and grain depression for insurance-grade drying logs.

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CARRIER AUDIT CERTIFICATE

Standard: IICRC S500 Psychrometric Chamber Audit

Date / Time: Generated Live

Job / Claim: Field Drying Chamber Log

Contractor: Proof Certified Field Operator

Chamber Psychrometric Readings

Dry Bulb Temperature (°F)

Relative Humidity (% RH)

Dehumidifier Exhaust (Grain Depression)

Dehu Exhaust Temp (°F, Optional)

Dehu Exhaust RH (%, Optional)

Specific Humidity (GPP)
78.5
Normal Ambient Air

Dew Point (°F)

60.1°F

Vapor Pressure (inHg)

0.52 inHg

Grain Depression (Δ GPP)

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Psychrometric GPP & Dew PointCalculator

Chamber Psychrometric Readings

Dehumidifier Exhaust (Grain Depression)

Psychrometric GPP & Dew Point
Calculator