LGR vs Conventional vs Desiccant Dehumidifiers
Which dehumidifier technology is right for water damage restoration? IICRC S500 specifies LGR as the baseline — here’s when pros switch to desiccant and why consumer units fail.
By Marcus Reed, IICRC WRT · Updated July 2026
From the Field: “Ninety percent of residential jobs are finished with LGR units. We only pull out desiccants for hardwood floors, cold-weather jobs, or when a homeowner waited too long and we need maximum grain depression on concrete.” — Marcus Reed, IICRC WRT+AMRT
Side-by-Side Comparison
| Technology | Best For | Temp Range | Efficiency | Equipment Cost | IICRC Class | Notes |
|---|---|---|---|---|---|---|
| LGR (Low Grain Refrigerant) | Most residential & commercial restoration | 33–95°F | Highest — extracts 5–8 lbs/kWh | $1,200–$3,000 | Class 1, 2, 3 | Industry standard for IICRC S500 drying. Required for insurance documentation. |
| Conventional Refrigerant | Mild humidity control, crawl spaces | 65–95°F | Moderate — 2–4 lbs/kWh | $300–$900 | Class 1, 2 | Freezes in cold environments. Not suitable for active water damage restoration below 65°F. |
| Desiccant | Cold environments, Class 4 drying, hardwood | 0–120°F | Lower — 1–2 lbs/kWh, but works in any temp | $1,500–$5,000+ | Class 4 (specialty materials) | Preferred when ambient temperature is below 55°F or when drying concrete, masonry, or hardwood floors. |
Why LGR Is the S500 Standard
The IICRC S500 Standard for Professional Water Damage Restoration specifies grain depression — the reduction in moisture content from ambient air to supply air — as the measurement of drying effectiveness. LGR dehumidifiers achieve grain depression values of 50–90 grains/lb, roughly double that of conventional refrigerant units.
This matters because insurance documentation requires psychrometric reports showing daily measurements of temperature, relative humidity, and dew point at multiple monitoring points. A job documented with consumer equipment has no verifiable drying log and may face claim disputes.
When Desiccant Wins
- →Class 4 (specialty drying): Wet hardwood floors, concrete walls, masonry require dew points below 40°F — only achievable with desiccant.
- →Cold environments: Below 55°F, LGR coils ice over and capacity drops to near zero. Desiccant operates down to 0°F.
- →Delayed response: When a homeowner waited 5+ days, structural materials absorb deeply. Desiccant’s lower dew point pulls bound moisture from concrete.
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Frequently Asked Questions
What type of dehumidifier do water damage restoration pros use?
IICRC-certified restoration contractors use LGR (Low Grain Refrigerant) dehumidifiers as the standard for most residential and commercial jobs. LGRs extract more moisture per kilowatt-hour than conventional units and operate effectively down to 33°F. Desiccant dehumidifiers are added for Class 4 jobs (wet concrete, masonry, hardwood) or when ambient temperatures drop below 55°F.
Why can't I just use a store-bought dehumidifier for water damage?
Consumer dehumidifiers (like a typical Frigidaire or hOmeLabs unit) are conventional refrigerant units rated for 50–70 pints/day at AHAM standard conditions (80°F, 60% RH). In real water damage conditions — lower temperatures, very high humidity — they perform at 20–30% of rated capacity. Professional LGR units extract 100–175 pints/day in actual conditions. Using a consumer unit on a flooded basement typically results in mold growth within 72 hours regardless of how long it runs.
When do restoration companies use desiccant dehumidifiers?
Desiccant dehumidifiers are specified under IICRC S500 for three scenarios: (1) Class 4 drying — intrusion into concrete, masonry, or hardwood requiring extremely low dew point; (2) temperatures below 55°F where refrigerant coils would ice over; (3) very large commercial structures where the heat output of a desiccant unit aids evaporation. They're rarely needed for typical residential flooding.
Does my insurance care what type of dehumidifier was used?
Yes, in practice. Insurance adjusters reviewing claims expect to see IICRC S500-compliant drying records with equipment logs from LGR units. Restoration companies submit psychrometric reports showing daily moisture readings, equipment runtime, and grain depression progress. A job dried with consumer equipment will not produce these records, which can complicate or reduce claim payouts.
How many LGR dehumidifiers are needed for a water damage job?
IICRC S500 specifies one LGR dehumidifier per affected room or per AHAM-rated capacity calculation based on cubic footage and materials. For a typical 1,000 sq ft basement, a contractor might deploy 2–4 commercial LGR units plus air movers. The drying plan is documented in a psychrometric report and adjusted daily.