Choosing the right size dehumidifier is critical to effectively controlling moisture, preventing mold growth, and protecting your space, equipment, or products. An undersized unit will run constantly without achieving the desired humidity level, while an oversized one may lead to unnecessary energy consumption and higher costs.

 

How to Calculate the Correct Dehumidifier Size

Step 1: Understand Dehumidifier Capacity

Dehumidifier capacity is typically measured in liters per day (L/day), indicating how much moisture the unit can remove from the air within 24 hours under standard conditions (usually 30°C / 80% RH).

As a general rule:

Light moisture issues require a lower capacity

Persistent or high-humidity environments require higher capacity

 

Step 2: Calculate Room Size

Start by calculating the volume of your space:

Room Area (㎡ or sq. ft) × Ceiling Height

For example:

A 100㎡ space with a 3m ceiling = 300 m³

A 1,000 sq. ft room with a 10 ft ceiling = 10,000 cubic feet

Larger volumes naturally require higher-capacity dehumidifiers.

 

Step 3: Assess Humidity Severity

Room size alone is not enough. You must also consider how damp the environment is.

High or very high humidity can double the required capacity, even in the same-sized space.

 

Step 4: Consider Environmental Factors

Several real-world conditions increase moisture load:

Poor ventilation

Cold temperatures

Water intrusion or leaks

Plant transpiration (grow rooms, greenhouses)

Industrial processes

If any of these apply, selecting a higher-capacity unit is strongly recommended.

 

Why a 70L Dehumidifier Is a Smart Choice

A 70-liter dehumidifier is ideal for medium-sized spaces with consistent humidity issues, such as:

Grow rooms and drying rooms

Basements and garages

Small warehouses or workshops

Commercial storage rooms

Key advantages:

Balanced capacity and energy efficiency

Stable humidity control without short cycling

Suitable for continuous operation

For most spaces between 200–400 m³ with moderate to high humidity, a 70L grow room dehumidifier provides reliable performance. Preair Guard70 dehumidifier is a 70L/D capacity machine with improved dehumidification performance.

 

When You Need a 120L Dehumidifier

A 120-liter dehumidifier is designed for large or high-load environments, including:

Large grow facilities

Industrial workshops

Warehouses and logistics centers

Food processing and packaging areas

Why choose 120L:

Handles extreme moisture loads efficiently

Faster pull-down time after humidity spikes

Reduced the number of units needed for large areas

If your space exceeds 400 m³, or humidity is consistently above 70–80% RH, a 120L commercial dehumidifier for grow room ensures long-term stability and protection. Preair Guard120 dehumidifier is an industrial-size unit that removes 120 liters of water per day @AHAM. If you want to find a reliable dehumidifier supplier, don't hesitate to get in touch with us before making a decision.

Final Recommendation

If you are unsure between sizes, it is almost always better to choose the higher capacity. A properly sized 70L or 120L dehumidifier will:

Operate more efficiently

Last longer due to reduced strain

Maintain stable humidity levels

For medium to large commercial, agricultural, or industrial applications, 70L and 120L dehumidifiers represent the most cost-effective and reliable solutions.