All three types remove moisture from the air, but they do it differently and shine in different conditions. Here is how to tell which one a drying job calls for.
A dehumidifier that works well in a warm, damp basement can struggle in a cold garage, and one that dries a cold warehouse can be overkill for a bathroom leak. Restoration crews choose between three families of machine: conventional refrigerant, low grain refrigerant (LGR) and desiccant. Each trades off cost, drying power, temperature range and setup work.
Dehumidifiers are one half of the drying system. They work together with air movers that push moisture off surfaces. If you are new to the process, start with how to dry out a flooded room.
A conventional refrigerant unit pulls room air across cold coils. Water vapor condenses on the coils, drips into a drain or tank and the drier air is returned to the room. It works like the dehumidifier many homeowners know, scaled up for restoration.
These units do their best work in warm, humid air. Restoration sources describe the best range as roughly 70 to 90 degrees Fahrenheit, and note they have limited ability to keep pulling moisture once the air has already become fairly dry. They suit smaller, simpler losses or work as backup units.
LGR stands for low grain refrigerant. The refrigerant coil is the same idea, but the air is pre-cooled before it reaches the coil, usually with a heat exchanger. That extra step lets the machine keep condensing water at lower humidity levels, where a conventional unit stops being effective. Humidity in drying work is often measured in grains of moisture per pound of air, which is where the name comes from.
LGRs are the most common type in restoration and rental fleets. They suit most residential and small commercial water losses, especially in heated, humid spaces. Like all refrigerant units, they lose efficiency as spaces get cool, and heating the space or switching to another type may be needed in cold conditions.
A desiccant unit does not use cold coils. A wheel coated with a moisture-absorbing material, often silica gel, rotates through the room air and picks up water vapor. A separate stream of heated air then drives the moisture out of the wheel so it can absorb again, and that warm, moist air is exhausted. Because it does not depend on condensation, a desiccant unit keeps working in cool conditions, including below freezing, and can reach very low humidity.
That makes desiccants the choice for difficult jobs: cold or unheated buildings, structures that cannot be warmed enough for refrigerant units, and losses involving dense, hard-to-dry materials such as hardwood or masonry. The tradeoffs are that they use more energy for the water they remove, generally need ducting to carry the warm, moist exhaust out of the drying area and are best set up by someone experienced.
The table summarizes the general differences. Individual machines vary, so the manufacturer's rating and instructions come first.
| Feature | Conventional | LGR | Desiccant |
|---|---|---|---|
| How it removes water | Condenses on cold coils | Pre-cools air, then condenses on coils | Absorbs onto a wheel, which is regenerated with heat |
| Best conditions | Warm, humid air | Warm to moderate temperatures and most homes | Cool, cold or very dry targets |
| Low humidity ability | Limited | Better than conventional | Strongest |
| Setup | Simple | Simple | Often needs ducted exhaust |
| Typical use | Small or simple losses | Most residential and small commercial jobs | Hard drying jobs and cold structures |
Start with temperature. If the building is heated and the materials are common wet drywall, carpet and framing, an LGR is the normal pick. If the space is cold, unheated or has been wet a long time with dense materials in play, ask whether a desiccant is appropriate. Add quantity based on the size of the space and the amount of wet material, and monitor moisture readings daily to see if the setup is working.
Whatever the type, run it in a closed space, drain it properly and keep it running until materials are dry. Tell us about your job in the dehumidifier rental request and we will help narrow the choice. For jobs that involve contaminated water, see the categories and classes guide first.
Rental listings and manufacturer sheets quote capacity in pints or gallons of water removed per day, and the numbers depend on the test conditions behind them. A rating at warm, humid conditions will not hold in a cool, drier room. When comparing machines, look at the conditions the rating applies to, and treat a high number at ideal conditions as a ceiling and not a promise.
Desiccant units are typically rated by the volume of air they process and the amount of water removed per hour, and the exhaust is a separate stream that needs a path out of the drying area. Ask about electrical requirements for any unit, because commercial machines can draw significantly more power than household equipment.
Putting a conventional refrigerant unit in a cold space and wondering why nothing comes out of the drain is a frequent story. So is running a desiccant unit without ducting its warm, moist exhaust, which can cancel out much of the benefit. Others use too few machines for the volume of wet material, or leave doors open so the unit is working against the whole outdoors.
Monitoring avoids most of these problems. If daily readings show the materials are not drying, the equipment, the space or the setup needs changing, and the answer is not simply to wait longer.
If the unit you rent has a humidistat or a built-in readout, treat it as a rough guide only. A meter in the building materials is what tells you whether the structure itself is drying, since the air can read dry while thick materials still hold water.
LGR stands for low grain refrigerant. It refers to a refrigerant dehumidifier with extra pre-cooling that lets it keep removing moisture at lower humidity than a conventional unit.
Not always. Desiccants handle cold and very dry targets better, but they use more energy and often need ducting. LGRs are simpler and common for most heated residential jobs.
For a small spill, maybe. For a wet structure, commercial units remove far more moisture and are built to run continuously.
LGR units generally do not. Desiccant units usually do, to carry their warm, moist exhaust out of the drying area. Follow the instructions for the unit you rent.
Tell us what is wet and what you need, and we will reply with availability and terms.