Quick answer: Use a desiccant dehumidifier on a water damage job when the building is cold (below about 15–18 °C), when you must dry dense materials such as hardwood floors, concrete, plaster or masonry that need very dry air, or when you want to duct dry air into a tented drying chamber. Desiccant units keep producing very dry air at low temperatures, where refrigerant (LGR) units ice up and slow down. They need a reactivation exhaust ducted outside, and they warm the process air, which helps drying. In warm buildings with ordinary drywall and carpet, refrigerant units are usually more efficient.
Quick answer
- Desiccant: cold sites, dense materials, very dry air, drying chambers.
- Refrigerant (LGR): warm sites, typical drywall/carpet jobs.
- Always duct the reactivation (wet) air outdoors.
Desiccant vs refrigerant on restoration jobs
| Condition | Better choice | Why |
|---|---|---|
| Unheated building, winter, below about 15 °C | Desiccant | No coil icing; output stays dry |
| Hardwood floors, concrete, plaster, masonry | Desiccant (often with a drying mat or tent) | Very low vapor pressure pulls water out of dense materials |
| Warm building, drywall, carpet, pad | Refrigerant (LGR) | Lower energy per litre in warm, humid air |
| Large commercial space with ducting | Desiccant or large LGR units | Desiccant output can be ducted to specific areas |
| Very humid, warm early stage of a job | Refrigerant first | Removes bulk moisture efficiently; switch to desiccant for the final dry-down if needed |
How a desiccant dehumidifier works on site
A slowly rotating wheel coated with desiccant (often silica gel) adsorbs water from the process air, which leaves dry and warmer. A smaller reactivation air stream is heated and passed through the wheel to drive the water out; this warm, wet air must be ducted outside the building. See how desiccant dehumidifiers work.
Setup on a job
- Contain the area with plastic sheeting where possible, so the dry air works on the affected zone.
- Duct the reactivation exhaust outside through a window panel or door, sealed. Never exhaust it into the building.
- Take reactivation intake air from outside or from an area away from the exhaust.
- Duct process air into the drying zone or under a tent over the wet floor; return air from the zone.
- Add air movers across wet surfaces.
- Measure daily: outlet and room moisture content (g/kg or gpp), material readings vs dry standard; see water damage drying log.
Drying hardwood floors and concrete
- Tent or mat systems: cover the wet floor with plastic or drying mats and feed desiccant-dried air under it, so very dry air works directly on the surface.
- Warmth helps: the warm process air from a desiccant unit raises the material temperature, which speeds moisture release.
- Patience: dense materials dry slowly; expect days to weeks. Test concrete with ASTM F2170 probes before refinishing (ASTM F2170); see drying a concrete floor after a leak.
Sizing
Size from the process airflow and the volume of the drying zone: the dry air should replace the zone's air several times an hour, and the moisture removal at the site's inlet condition should exceed the evaporation rate from the materials. Ratings for desiccant units are usually at 20 °C / 60 % RH; at colder, drier inlet air the L/day falls, but the outlet stays very dry.
Model data
| Model | Removal (20 °C / 60 % RH) | Process air | Reactivation air | Power | Supply |
|---|---|---|---|---|---|
| RY-300M | 48 L/day | 320 m³/h | 110 m³/h | 2 kW | 220 V, 1-phase |
| RY-600M | 72 L/day | 580 m³/h | 200 m³/h | 4.5 kW | 220 V, 1-phase |
| RY-750M | 108 L/day | 750 m³/h | 250 m³/h | 7 kW | 380 V, 3-phase |
| RY-1000M | 180 L/day | 1,000 m³/h | 400 m³/h | 11 kW | 380 V, 3-phase |
Single-phase models are easier to power on restoration sites. Full range on our desiccant dehumidifier page; operating range −10 to +55 °C.
Power and safety
- Desiccant units draw more power than LGR units of similar size, mostly for the reactivation heater; plan circuits accordingly.
- Use protected circuits and keep cables out of water.
- Contaminated water (sewage, flood) needs containment and protective equipment before air is moved; the US EPA notes fans should not be used until the water is known to be clean.
FAQ
Frequently asked questions
When should I use a desiccant dehumidifier for water damage?
In cold buildings, for dense materials such as hardwood, concrete and plaster, and for tented drying chambers.
Are desiccant dehumidifiers better than LGR?
In cold conditions and for very dry air, yes. In warm buildings with typical drywall and carpet, LGR units are usually more efficient.
Do desiccant dehumidifiers need to be vented outside?
Yes. The reactivation air carries the removed water as warm, humid air and must be ducted outdoors.
Can a desiccant dehumidifier dry hardwood floors?
Yes, often with a tent or drying mats that feed dry air directly to the floor surface.
Sources
- IICRC S500, Standard for Professional Water Damage Restoration.
- ASTM F2170.
- US EPA, Mold course chapter 4.
