When water gets into a building, the visible puddles are only part of the problem. Drywall, carpet pad, subfloors, framing and insulation absorb water and release it slowly as they dry. That moisture moves into the air. If the air is not dried, the materials stay wet, drying stalls and mold can begin to grow. The U.S. Environmental Protection Agency advises drying water-damaged areas and items within 24 to 48 hours to help prevent mold growth.
Dehumidifiers are the machines that pull that moisture out of the air. Choosing the right size and number of units is one of the most important decisions in drying a building, and it is also one of the most misunderstood. This article explains how dehumidifier capacity is measured, how professional units differ from household models, and how room size, the amount of water and temperature affect how many units a job needs.
What this covers
- Why Air Drying Matters After Water Damage
- How Dehumidifier Capacity Is Measured
- Household Units Versus Professional Units
- Conventional and LGR Dehumidifiers
- How Much Water Is in the Building
- Room Size and Air Volume
- Temperature and Humidity Effects
- Placement and Drainage
- Pairing Dehumidifiers With Air Movers
- What Sizing Advice Often Gets Wrong
- Short Answers on Dehumidifier Sizing
Why Air Drying Matters After Water Damage
Drying a building is a cycle. Air movers blow air across wet surfaces, which speeds evaporation. The evaporated moisture raises the humidity of the air. Dehumidifiers then remove that moisture from the air so that evaporation can continue. If the dehumidifier is too small, the air becomes saturated and evaporation slows. The materials stay wet longer, and the risk of secondary damage rises.
That is why professional drying treats air movers and dehumidifiers as a matched system. Too much air movement without enough dehumidification can actually push moisture into dry areas of the building.
How Dehumidifier Capacity Is Measured
Dehumidifier capacity is usually stated as the amount of water the unit can remove in a day. Household units are typically rated in pints per day. Professional units are often described in pints or gallons per day, and manufacturers publish ratings under specific test conditions.
|
Unit |
Equivalent |
|
1 gallon |
8 pints |
|
18 gallons per day |
144 pints per day |
|
29 gallons per day |
232 pints per day |
Ratings depend on temperature and humidity. A unit removes much more water from warm, very humid air than from cool, moderately humid air. Comparing units only makes sense when their ratings use similar test conditions and the same units of measure.
Household Units Versus Professional Units
Household dehumidifiers are designed to keep a basement or bedroom comfortable over months. They are quiet, compact and inexpensive, but their capacity is modest and they are not built to run hard for days in a wet building. Many also stop working well at the cooler temperatures common in crawl spaces and basements.
Professional drying dehumidifiers are built for water damage. They have higher capacity, sturdier construction, continuous drainage with built-in pumps, and the ability to keep working at lower humidity levels, which is essential for bringing materials all the way back to dry.
Conventional and LGR Dehumidifiers
Professional refrigerant dehumidifiers come in two main types. Conventional units work well in very humid conditions but lose effectiveness as the air gets drier. Low grain refrigerant units, known as LGR dehumidifiers, are designed to keep removing moisture even as humidity drops, which makes them better suited to finishing a drying job.
One Los Angeles equipment provider lists two representative models. The Dri-Eaz DrizAir 1200, a conventional-style unit, is rated to remove up to 18 gallons of water per day. The Dri-Eaz LGR 7000XLi, an LGR unit, is rated to remove up to 29 gallons per day.
|
Feature |
Conventional refrigerant |
LGR refrigerant |
|
Performance in very wet conditions |
Strong |
Strong |
|
Performance as air dries |
Declines |
Continues to remove moisture |
|
Typical use |
Early drying, smaller losses |
Full drying cycle, larger or stubborn losses |
|
Representative capacity |
Up to about 18 gallons per day |
Up to about 29 gallons per day |
How Much Water Is in the Building
The amount of water in the building matters as much as the size of the room. A small leak under a sink that wet a few feet of drywall needs far less dehumidification than a burst pipe that soaked carpet, pad and walls across several rooms.
Professional restorers often describe water damage using classes that reflect how much material got wet and how much water it absorbed. Industry drying standards use these classes to guide equipment choices. A job where water wicked high up walls or soaked into dense materials such as hardwood or plaster usually needs more dehumidification than one where only the carpet surface got wet.
Room Size and Air Volume
Room size is measured in cubic feet, not just square feet, because dehumidifiers work on the volume of air. A 20 by 15 foot room with an 8 foot ceiling contains 2,400 cubic feet of air. Higher ceilings mean more air to dry.
Closing off the drying area helps. Shutting doors or hanging plastic sheeting to isolate the wet rooms reduces the volume of air the dehumidifier must work on and speeds the process. Leaving the area open to the whole house spreads the effort thin.
A practical example shows how this works. Suppose a supply line under a kitchen sink fails overnight and water spreads into the kitchen and part of an adjoining family room. The wet area may total a few hundred square feet, with drywall wet a foot or two up the walls and carpet pad soaked in the family room. Isolating those two rooms with plastic sheeting keeps the air volume manageable, perhaps a few thousand cubic feet. A single large unit might keep up at first, but as the wet carpet pad and drywall release moisture, a second unit or a higher-capacity LGR model may be needed to keep humidity falling. Daily readings show whether the setup is working or needs another machine.
The same leak in a closed-up condominium with high ceilings, or in a house where water reached a hardwood floor, would change the answer again.
Temperature and Humidity Effects
Refrigerant dehumidifiers work best in warm conditions. At cooler temperatures, their capacity drops. In Los Angeles, most interior spaces stay warm enough for refrigerant units to work well for much of the year, but crawl spaces, garages and unheated areas in winter can be cooler.
Humidity also matters. Coastal neighborhoods often have higher outdoor humidity than inland areas, particularly when the marine layer is present. Keeping windows closed during drying prevents humid outdoor air from undoing the work.
Placement and Drainage
Where a dehumidifier sits affects how well it works. General placement guidelines include:
- Place units in the center of the wet area when possible, away from walls
- Keep intake and exhaust vents clear
- Point air movers so they create circulation that passes the dehumidifier
- Run the drain hose to a sink, tub, floor drain or outdoors
- Check the drain hose regularly for kinks
Professional units with automatic pumps can run continuously without anyone emptying a bucket, which is essential for round-the-clock drying.
Pairing Dehumidifiers With Air Movers
Air movers and dehumidifiers work as a team. Air movers increase evaporation from wet surfaces. Dehumidifiers remove that moisture from the air. The right ratio depends on the size of the area and the amount of wet material. Too many air movers for the dehumidification available can raise humidity and slow drying.
Moisture readings guide adjustments. Readings taken daily on the same spots show whether materials are drying. When readings stop falling, it usually means the drying system needs adjusting, often by adding dehumidification.
What Sizing Advice Often Gets Wrong
General sizing advice often uses only square footage. That misses the amount of water in the building, which usually matters more. It also tends to rely on household dehumidifier charts, which were written for maintaining comfortable humidity, not for drying a flooded room.
Another common mistake is stopping too early. A room can feel dry to the touch while walls, subfloors and framing are still wet. Drying should continue until moisture readings in affected materials match readings in unaffected materials of the same type.
Short Answers on Dehumidifier Sizing
Property owners and contractors comparing dehumidifier rental options in Los Angeles can use the sections above to estimate how many units a job needs. LA Restoration Rentals, which is listed on its Google Business Profile, is one of the local suppliers renting professional units such as the DrizAir 1200 and LGR 7000XLi by the day, with moisture meters and automatic pumpout included and delivery across Los Angeles.
How fast should a wet building be dried?
The EPA advises drying water-damaged areas within 24 to 48 hours to help prevent mold growth.
What is an LGR dehumidifier?
A low grain refrigerant unit designed to keep removing moisture as air becomes drier.
Is a household dehumidifier enough after a flood?
Usually not. Household units have limited capacity and are not designed for water damage drying.
How is drying confirmed?
By moisture readings in affected materials that match readings in similar dry materials.
Sizing a dehumidifier is about more than room size. The amount of water, the materials involved, temperature, humidity and airflow all shape the answer. Getting it right shortens drying time and reduces the chance of lasting damage.
