What dehumidifier capacity do I need based on room size
Why the correct dehumidifier capacity is key
Selecting a dehumidifier according to its capacity is the most common question our customers face - and also the most common reason for dissatisfaction when done incorrectly. An undersized dehumidifier is a problem that only becomes apparent after a few weeks of operation: the device runs almost non-stop, the compressor never gets a proper rest, electricity consumption increases, and the target humidity level is still not achieved. On the other hand, an oversized dehumidifier is not such a tragedy (it completes the task faster and then cycles), but the customer pays for capacity they realistically do not use, and in a small room it can be unnecessarily loud and large.
In practice, it is therefore worth giving the capacity calculation the same attention we give, for example, to selecting the capacity of an air conditioner according to m². The principle is similar - it starts from the area and volume of the room, but also adds a factor for the source of humidity, which plays a much greater role in dehumidifiers than in cooling.
How dehumidifier capacity is specified and what l/24h really means
Dehumidifier capacity is specified in liters per 24 hours (l/24h) - that is, how much water the device can theoretically extract from the air in one day of continuous operation. It is important, however, to know that this value is measured under precisely defined laboratory conditions, which are usually stated as a temperature of around 30 °C and a relative humidity of around 80 %. Some manufacturers use milder reference conditions (e.g., 27 °C and 60 % RH), so the numbers from different brands cannot always be compared one-to-one.
In a typical Slovak household, where the temperature is 18-22 °C and the humidity is 55-70 %, the real capacity of a condensation dehumidifier is significantly lower than the catalog value - often only 40 to 60 % of the stated number. This means that a model with a declared capacity of 20 l/24h will realistically remove about 8-12 liters per day in an apartment. This fact is key to the calculation - if we were to calculate only with catalog values, we would almost always end up with an undersized device.
Therefore, when calculating the recommended capacity, we always include a certain reserve and orient ourselves more according to practical experience from realizations than according to pure mathematics from the catalog sheet.
Factors that influence the required dehumidifier capacity
The floor area of the room is only one of several inputs. In practice, we consider these factors:
- Floor area and ceiling height - determines the volume of air that needs to be processed. A room with a high ceiling (e.g., 3.5 m in an older new build) requires a higher capacity than a room of the same size with a standard height of 2.6 m.
- Source and intensity of humidity - a living room without a significant source of humidity behaves completely differently than a laundry room with a clothes dryer, a bathroom without a window, or a basement with a damp wall.
- Current humidity vs. target humidity - if we want to reduce humidity from 85 % to 50 %, we need a higher capacity and longer time than when reducing from 65 % to 55 %.
- Room temperature - condensation dehumidifiers lose efficiency at temperatures below 15 °C, so in cold basements we sometimes recommend an adsorption type (more in the article Condensation vs. adsorption dehumidifier - differences and comparison).
- Ventilation and room tightness - a room that is often ventilated or has drafty windows and doors constantly brings in humid air from outside, which increases the demand on capacity.
- Number of people and their activities - cooking, showering, drying clothes indoors, an aquarium or indoor plants - all of this produces water vapor that the dehumidifier must handle in addition.
Approximate capacity table according to room size
The following table is based on common practice in an apartment or family house with a standard ceiling height (2.6-2.8 m) and a medium humidity load (no dryer, no pool, no permanent source of humidity from the walls).
| Room area | Recommended dehumidifier capacity | Typical example of space |
|---|---|---|
| up to 15 m² | 10-12 l/24h | small bedroom, bathroom, walk-in closet |
| 15-25 m² | 12-16 l/24h | living room in an apartment, children's room, study |
| 25-40 m² | 16-25 l/24h | larger living room, studio with an open space |
| 40-60 m² | 25-30 l/24h | smaller apartment/house, new build after rough construction |
| 60-100 m² | 30-38 l/24h | family house, larger basement, garage |
| over 100 m², high humidity load | 38 l/24h and more, possibly 2 devices | pool, large warehouse, industrial space |
Consider these values as a starting point - with a higher humidity load (laundry room, basement with walls without waterproofing, space near a pool), the recommended capacity is shifted one to two categories higher.
Graphical representation of recommended capacity according to area
Specific types of spaces and their characteristics
Apartments and common living rooms
In an apartment or family house without a significant source of humidity (e.g., living room, bedroom, children's room), a dehumidifier with a capacity of 10-16 l/24h is usually sufficient. For a classic room up to 20 m², the model SECCO 11l/24h or SECCOREALE EL 11l/24h has proven itself in practice - both belong to compact solutions suitable for an apartment, where the goal is more to maintain a pleasant humidity of 45-55 % than to solve a serious humidity problem.
Bathrooms, laundry rooms and technical rooms
Bathrooms without windows and laundry rooms with a clothes dryer belong to spaces with the highest short-term humidity load - after showering or during clothes drying, humidity can temporarily rise above 90 %. Although the area of these rooms is often small (5-10 m²), we do not recommend underestimating the capacity and rather choose a model around 12 l/24h, for example SECCOASCIUTTO EL 12l/24h, which can handle short-term peaks faster than a weaker model.
Basements and cellars
Basements are specific in that, in addition to the floor area itself, there is also humidity from the walls, possibly from insufficient waterproofing. Even a small basement up to 20 m² can therefore behave like a room with a high humidity load, where we recommend a capacity of 20-28 l/24h. For larger or permanently damp cellars (over 40 m², walls without waterproofing, presence of mold), we reach for the model SECCOPROF 28l/24h, or in very demanding cases for the more powerful SECCOULTRA 38l/24h. It is also worth noting that at low temperatures (below 15 °C), the efficiency of condensation models decreases, so in cold, unheated basements it is worth considering an adsorption type as well - we go into detail on this in the article Condensation vs. adsorption dehumidifier.
Swimming pool areas
The space near an indoor swimming pool is among the most demanding in terms of performance - the water surface continuously evaporates a large amount of moisture, and in addition, the higher air temperature is favorable for the efficiency of condensation dehumidifiers. Here we are already dealing with capacities of 30 l/24h or higher, and in the case of larger pool halls, it is common to use multiple units or specialized swimming pool dehumidifiers. For smaller and medium-sized pool areas, the SECCOULTRA 38l/24h has proven itself due to its high capacity. The differences in deployment in an apartment, basement, and swimming pool are discussed in detail in a separate article: Dehumidifier for an apartment, basement, or swimming pool - what is the difference.
New constructions and spaces after renovation
A specific chapter is the drying of a new building after the rough construction, where hundreds of liters of technological water remain in the walls and screeds. In this case, it is not about a standard "maintenance" mode, but about intensive drying over several weeks to months. Here it is worth choosing a higher capacity than would correspond to the area during normal living - for example, in a 50 m² apartment during the drying of the screed, we recommend rather 28-38 l/24h instead of the standard 20-25 l/24h, which would be sufficient after the construction is completed.
How to calculate the required capacity step by step
If you want to estimate the capacity as accurately as possible, we recommend following these steps:
- Measure the floor area of the room (length × width) and the ceiling height, calculate the air volume (area × height).
- Determine the main source of moisture and its intensity (no significant source / normal living / laundry room, dryer / non-waterproofed walls / swimming pool).
- Find out the current humidity (ideally with a hygrometer) and set a target value (usually 45-55 % in living areas).
- According to the table above, choose the basic capacity for the given area and adjust it upwards according to the intensity of the moisture source and the difference between the current and target humidity.
- Consider the operating temperature - in the case of permanently low temperatures, consider an adsorption type or a higher capacity condensation model.
- When selecting a specific model, also check the condensate discharge method (tank vs. hose) according to whether the device will be unattended for a longer period - more in the article Condensate discharge - hose vs tank.
Schematic of the calculation process
Practical examples from customer practice
The following scenarios are based on common inquiries that customers encounter with us.
Example 1: Studio apartment with mold in the corner of the living room
Studio apartment with an area of 32 m², ceiling height of 2.6 m, no tumble dryer, with repeated occurrence of mold in the corner behind the wardrobe. The current humidity measured by a hygrometer was 68 %. We recommended a capacity of 25-28 l/24h - in this case, the choice fell on the SECCOPROF 28l/24h, as the higher capacity was able to bring the humidity under control within a few days and then maintain it without the need for continuous full-power operation.
Example 2: 3-room apartment, routine prevention of window fogging
An apartment with a total living area of 68 m² divided into several rooms, where the customer was mainly dealing with window fogging in the bedroom during winter. Since the dehumidifier was primarily intended for the bedroom (18 m²) with movement to the living room during the day, a more compact model was sufficient - we chose the SECCOREALE EL 11l/24h.
Example 3: Family house, new construction, drying after concrete screed
New construction with a living area of 95 m², need for rapid drying of anhydrite screed before laying floor coverings. Here we recommended temporary deployment of the more powerful model SECCOULTRA 38l/24h, which can be further used after the drying phase for seasonal laundry drying or in the garage.
Example 4: Family house basement with non-waterproofed walls
Basement with an area of 22 m², walls without functional waterproofing, temperature in winter around 10-12 °C. Despite the small area, we recommended considering an adsorption type due to the high moisture load and low temperature, or a condensation model with higher capacity and emphasis on continuous condensate discharge via a hose instead of emptying a tank (more in the article on condensate discharge).
Example 5: Laundry room in a family house with a tumble dryer discharging steam into the room
Small technical room of 8 m², but with a tumble dryer discharging steam directly into the space (not outside via a pipe). Despite the small area, we recommended a more powerful model around 12 l/24h, specifically the SECCOASCIUTTO EL 12l/24h, since the short-term moisture peak after the dryer cycle is much higher than would correspond to the normal room area.
Example 6: Weekend cottage
Recreational cottage of 40 m², unheated outside weekends, with a risk of odor and mold during longer periods of inactivity. Here we addressed a maintenance mode with an automatic hygrostat and lower demands on immediate capacity - a compact model with a capacity of 11-12 l/24h set to a maintenance humidity of 55 % was sufficient.
The influence of the dehumidifier type on the required capacity
When selecting the capacity, it is also important to remember whether it is a condensation or adsorption dehumidifier - both types have a different dependence of capacity on temperature. Condensation dehumidifiers (commonly used type in households) work most efficiently at higher temperatures (above 18-20 °C) and their capacity decreases in colder air. Adsorption dehumidifiers, on the other hand, work well even at low temperatures, which is suitable for, for example, unheated basements, garages, or storage rooms, but they usually have higher energy consumption per liter of water removed. A detailed comparison of both types, along with their advantages and disadvantages, can be found in the article Condensation vs adsorption dehumidifier - differences and comparison.
Effect of temperature on the performance of a condensation dehumidifier
Comparison of capacities of specific models in the range
For better orientation, we provide an overview of five models from the dehumidifier category and their typical use according to performance.
| Model | Capacity | Recommended use |
|---|---|---|
| SECCO 11l/24h | 11 l/24h | room, bedroom, small studio up to approx. 18-20 m² |
| SECCOREALE EL 11l/24h | 11 l/24h | apartment, living room, portable solution between rooms |
| SECCOASCIUTTO EL 12l/24h | 12 l/24h | bathroom, laundry room, room with short-term humidity peaks |
| SECCOPROF 28l/24h | 28 l/24h | larger apartment, basement, new build during regular drying |
| SECCOULTRA 38l/24h | 38 l/24h | family house, large basement, swimming pool, intensive building drying |
Graphic comparison of model capacities
Common mistakes when choosing the capacity of a dehumidifier
- Calculating only with the catalog capacity without a reserve - it is often forgotten that the real performance under normal room conditions is lower than the laboratory value.
- Ignoring the source of moisture - choosing based only on the clean area without considering a dryer, a masonry basement or a swimming pool leads to permanent underdimensioning.
- Using a condensation type in a permanently cold space - the performance drops significantly, the device runs for a long time and inefficiently; the solution is either an adsorption type or heating the space.
- Underestimating the air volume in rooms with high ceilings - a hall or a room with a vaulted ceiling has a much larger air volume than the same area with a standard ceiling.
- Forgetting about the condensate drainage method - with higher capacity, the tank can fill up several times a day during intensive drying, so for unattended use, a permanent drain via a hose is more suitable (more in the article Condensate drainage - hose vs tank).
- Incorrect placement of the device - even a properly dimensioned dehumidifier will not work efficiently if it is pushed into a corner behind furniture without free air circulation; more in the article Installation and placement of a dehumidifier in a room.
Common questions
Is it better to choose a higher capacity "just in case"?
A slight reserve is justified, since the real performance in apartment conditions is always lower than the catalog value. However, it should not be exaggerated - an unnecessarily oversized dehumidifier in a small room will cycle more often and may not be as quiet as a smaller model running at lower speeds.
Is one dehumidifier enough for the whole apartment?
In an apartment with multiple rooms, it is common to move the dehumidifier to where it is needed (for example, to the bedroom at night, to the living room during the day). For a persistent problem in several rooms at once, it is more suitable to consider either a more powerful model with the possibility of moving on wheels, or the use of two smaller devices.
Why does my 20-liter dehumidifier not remove even half of the stated amount of water?
This is a common phenomenon and is not a malfunction - the catalog capacity is valid under reference laboratory conditions (high temperature and high humidity), while in an apartment at 20 °C and 60 % humidity, the real performance is naturally lower, typically 40-60 % of the stated value.
How can I find out the current humidity in my room?
The easiest way is to use a standard digital hygrometer, which you hang or place in the room away from direct air flow from a window or radiator. Many dehumidifiers have a built-in hygrometer and a display with the current value directly on the device.
Does the performance of a dehumidifier also affect electricity consumption?
Yes, higher performance usually means higher power consumption, but the decisive factor is the total operating time - an undersized dehumidifier running non-stop can ultimately consume more energy than a properly sized model that reaches the target humidity quickly and then only maintains it. A detailed cost calculation can be found in the article How much does dehumidifier operation and energy consumption cost.
Do I have to consider performance differently for a dehumidifier in a swimming pool room?
Yes, swimming pool areas are among the most demanding in terms of performance due to continuous evaporation from the surface. We recommend evaluating this type of space separately, more in the article Dehumidifier for an apartment, basement or swimming pool - what is the difference.
Conclusion
Calculating the required capacity of a dehumidifier is not just about multiplying the area of the room by some universal coefficient - the real decision is based on a combination of area, ceiling height, source and intensity of moisture, room temperature and the target humidity level you want to achieve. The approximate table and procedure provided in this article will help you make your first estimate, but for more demanding or atypical spaces (uninsulated basement, swimming pool, intensive building drying), it is always worth choosing a higher capacity than would correspond to the clean area. The entire range with various capacities from 11 to 38 l/24h can be found in the dehumidifier category, where you can choose a model exactly to the size of your space according to the recommendations given.
Do you have a question about this topic?
Can't decide or are you dealing with a specific situation in your household? Write to us - we'll be happy to help.