How big a dehumidifier do you need? Examples for different spaces
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The size of dehumidifier you need does not depend solely on the volume of the space in cubic metres. Volume is a good starting point, but temperature, the amount of moisture introduced, how well-sealed the space is, and how the dry air can circulate also affect your requirements. A crawl space, a cold loft, a garage and a storage room with the same volume may therefore require different solutions.
Quick answer: Start by calculating the volume of the room in m³, but use this only as a preliminary guide. Temperature, moisture levels, airtightness and intended use also affect the capacity required. Therefore, do not choose a dehumidifier solely on the basis that a specified maximum volume corresponds to the size of the room.
How to choose the right size of dehumidifier
The first step is to estimate the volume of air to be dehumidified.
For a standard rectangular space, you calculate as follows:
Floor area × ceiling height = volume in m³
For example, a 40 m² garage with a ceiling height of 2.5 metres has a volume of:
40 × 2.5 = 100 m³
The volume indicates the size category that may be appropriate, but two rooms, each measuring 100 m³, may still require dehumidifiers of different sizes.
Above all, you also need to bear in mind:
- The temperature. In cold, unheated spaces, the dehumidifier needs to work effectively even at low temperatures. Read more in our guide on dehumidifiers in sub-zero temperatures.
- How much moisture is added. Wet vehicles, ground damp, washing, damp goods and air leaks can result in significantly greater requirements than the volume alone would suggest.
- The density. If damp air is constantly entering through gaps, the dehumidifier will constantly have to deal with fresh damp air. Structural problems should therefore be rectified wherever possible.
- How the dry air spreads. In crawl spaces, lofts and larger premises, the air must be able to reach every part of the space, including behind partitions and in different zones.
The more moisture is introduced and the more conditions vary, the more important it is that the dehumidifier can cope even during periods when the need is greatest.
Different areas of application have different requirements
Two spaces with roughly the same volume may require completely different levels of dehumidification. The table provides a quick overview of what is particularly important in different environments.
| Space | Simplified volume | Important to bear in mind |
|---|---|---|
| Crawl space | 120 m² × 0.6 m = 72 m³ | Soil moisture, outdoor air, temperature and airtightness can result in a high moisture load despite a small air volume. |
| Garage | 40 m² × 2.5 m = 100 m³ | Wet or snow-covered vehicles and the repeated opening of doors can quickly increase the amount of moisture. |
| Cold wind | 10 m × 8 m, approximately 3 m at the ridge ≈ 120 m³ | Air leaks from the home and significant temperature fluctuations affect the humidity level. |
| Storage room | 25 m² × 2.4 m = 60 m³ | In a relatively compact storeroom with dry storage conditions, this volume may serve as a good initial selection. |
| Cellar | 60 m² × 2.2 m = 132 m³ | The temperature, intended use and cause of the damp determine which solution is appropriate. |
| Stock | 500 m² × 5 m = 2,500 m³ | Port traffic, temperature, perishable goods and storage climate requirements can have a significant impact on demand. |
| Laundry room | 150 m² × 4 m = 600 m³ | Water is supplied during operation, which can result in a significant need for dehumidification in relation to the volume. |
The examples are simplified. A larger volume in m³ does not automatically mean a greater need for dehumidification. A smaller space where a lot of moisture is introduced may place greater demands than a larger but dry and stable space.
Dehumidifiers for various applications
A crawl space measuring 120 m²
A crawl space measuring 120 m² with an average clear height of 0.6 metres has an air volume of:
120 × 0.6 = 72 m³
Despite the relatively small volume of air, a crawl space can be a challenging environment. Moisture can come from the ground, surface water, groundwater and outside air. When warm, moist air enters a cool crawl space, the temperature drops and the relative humidity rises. Under certain conditions, condensation can form on cold surfaces.
The density of the foundation, ground conditions, temperature and air distribution therefore need to be taken into account alongside the volume. At The Swedish National Board of Housing, Building and Planning provides further information on damp risks in crawl spaces.
In a crawl space with significant or varying damp problems, it is possible to EvoDry RCF 20 G1 be a model to evaluate. See also our guide on common causes of damp in crawl spaces.
40 m² garage
A 40 m² garage with a ceiling height of 2.5 metres has a volume of:
40 × 2.5 = 100 m³
How the garage is used has a significant impact on these requirements. A car that is wet from the rain or covered in snow can bring in large amounts of water in a short space of time, and every time the door is opened, the temperature and humidity levels change.
For a garage with a recurring source of moisture, EvoDry RCF 12 G1 be a model to evaluate. The choice must also take into account temperature, usage and the amount of moisture the vehicles bring in.
Cold attic space of approximately 120 m³
An attic that is 10 metres long, 8 metres wide and approximately 3 metres high at the ridge has, for simplicity’s sake, the following volume:
8 × 3 ÷ 2 × 10 = 120 m³
Moist indoor air can seep up through gaps in the loft floor. When the air cools in the cold loft, the relative humidity rises. These conditions are also affected by the season, the temperature and how well the dry air can circulate throughout the loft.
When circumstances call for greater capacity, it is possible to EvoDry RCF 20 G1 serve as a model for evaluation.
A 25 m² storage room
A storeroom measuring 25 m² with a ceiling height of 2.4 metres has a volume of:
25 × 2.4 = 60 m³
If the storage area is relatively airtight and the items stored are dry, conditions are often fairly stable. In that case, volume is a better first selection criterion.
For this type of space, a compact sorption dehumidifier such as EvoDry 6H 2.0 be a model to evaluate. Damp objects or significant leaks, on the other hand, may increase the need.
A 60 m² cellar
A 60 m² cellar with a ceiling height of 2.2 metres has an air volume of:
60 × 2.2 = 132 m³
A heated domestic cellar and a cool storage cellar can have completely different conditions. The cause of the damp is therefore at least as important as the volume.
If the problem is caused by water ingress or standing water, the underlying cause must be addressed. A dehumidifier is no substitute for the necessary structural repairs.
500 m² warehouse
A 500 m² warehouse with a 5-metre clear height has a volume of:
500 × 5 = 2,500 m³
A warehouse stocked with dry goods and with few door openings can have fairly stable conditions. A logistics warehouse with frequent deliveries, on the other hand, may experience significant fluctuations when outdoor air, wet vehicles, goods and packaging are brought in.
When designing the system, it is particularly important to know the temperature, how often the doors are opened, the humidity required for the goods, and how the dry air can be distributed throughout the premises.
For larger warehouses requiring continuous dehumidification, a professional sorption dehumidifier such as EvoDry 120 Pro serve as a model for evaluation.
Laundry room measuring 150 m²
A 150 m² laundry room with a ceiling height of 4 metres has a volume of:
150 × 4 = 600 m³
In this case, the volume says relatively little about the actual requirement. Water is supplied whenever operations are underway, and wet floors, vehicles and other surfaces continuously release moisture.
When designing the system, it is necessary to know, amongst other things, how often the hall is used, how much water is used, the temperature, the ventilation and the relative humidity you wish to maintain.
A professional sorption dehumidifier that EvoDry 120 Pro could be a model worth evaluating. However, it is not possible to determine the correct size based on 600 m³ alone.
What does l/24h mean in relation to m³?
When comparing dehumidifiers, both the recommended room volume in m³ and the dehumidification capacity in l/24h are often stated.
m³ describes how big the space is.
l/24h describes how much water the dehumidifier can remove over a 24-hour period under the specified temperature and humidity conditions.
Capacity varies as temperature and humidity change. It is therefore not possible to choose a dehumidifier based solely on the maximum number of litres per day.
Get help choosing a dehumidifier
Start by calculating the volume. Then assess the temperature, the amount of moisture being introduced, how well-sealed the space is, and how the dry air can circulate.
With our sizing tool for dehumidifiers you can make an initial selection based on the space available.
For large warehouses, car washes, production environments and other premises where a significant amount of moisture is introduced, the design calculations often need to be carried out in greater detail. In such cases, factors such as temperature, desired relative humidity, air change rate and operating hours are important elements of the design basis.
If you would like help with the entire solution, you can use the form below to request a quote.
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