Dry air does not mean a dry wall
People reasonably ask why a desert house needs dehumidifiers. Outside air here is dry most of the year, but a wet room is not. A soaked floor and wall can push indoor humidity well above the 60 percent EPA says to stay under. Air movers lift moisture off surfaces, and dehumidifiers remove it from the air before it soaks back in.
How equipment gets sized
| Equipment | Rule of thumb | What it means in a 12 by 12 room |
|---|---|---|
| Air movers | One per 10 to 16 linear feet of wall, plus one per closet | About four |
| Dehumidifier, Class 2 | Room cubic feet divided by 50 gives pints per day | About 23 pints a day at 8 foot ceilings |
What the readings mean
We take a dry standard from a room the water never reached. Then we read the wet areas each visit. Pin meters on wood and drywall, pinless meters on tile and floors, and a hygrometer for the air. When the wet readings match the dry standard, the drying is done. For drywall, damage can start at just over 1 percent moisture content, so close is not done.
Dense materials take longer
Concrete slabs, hardwood and plaster are what restorers call Class 4. They release water slowly. Hardwood that cupped from below should not be sanded until moisture is back to normal, or the boards end up crowned later.