Mould creeping along a wall, condensation streaming down the windows, paint flaking off in patches: these are the signals that push many households to buy a dehumidifier. The device can genuinely help, but only if it is the right type for the climate and the room, and only if the buyer understands what the specifications on the box actually measure. TechNews DevTop has reviewed the official guidance and manufacturer data to separate the useful numbers from the marketing ones.
- Target humidity: The US Environmental Protection Agency recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%. Spain’s building services regulation (RITE) sets design conditions of 40–50% in winter and 45–60% in summer.
- Compressor vs desiccant: Compressor (refrigerant) units perform best in warm, humid conditions above roughly 45% humidity; desiccant models are the better choice in cold rooms, with one British unit rated to operate from 1°C to 35°C.
- Litres per day are conditional: Declared extraction is almost always measured at 30°C and 80% humidity. One compressor model drops from 35 to 21 litres per day when tested at 27°C and 60%.
- Running costs: A 360W compressor unit draws 0.36 kWh per hour at full tilt, while a 623W desiccant model at maximum speed consumes around 5 kWh over eight hours.
Start with a number, then rule out the real causes
The first step is measurement, not shopping. A cheap hygrometer from a hardware store will show whether relative humidity sits persistently above 60%, the threshold at which ventilation alone often stops being enough. The EPA notes that condensation on surfaces can itself be a sign of elevated moisture.
Before spending money, it is worth eliminating problems a dehumidifier cannot fix. Consumer organisation OCU warns that these appliances do not attack the root cause, they only mitigate it: construction defects and water infiltration must be repaired. Daily ventilation is a good habit, though it guarantees little when the outside air is itself damp.
One overlooked factor is combustion. The EPA points out that kerosene heaters and similar unvented appliances produce water vapour and raise indoor humidity. A paraffin stove without an exterior flue can be feeding the very mould the household is trying to eliminate.
Compressor or desiccant: matching the machine to the climate
The choice hinges on temperature more than brand. Compressor units, also called refrigerant models, are the most common and work best at high temperatures with humidity above 45%, which makes them a natural fit for warm, humid coastal regions. Desiccant units use a material that absorbs moisture and perform better in low temperatures, suiting mountain homes, colder coastlines or properties near a river.
The mechanics differ. In a compressor unit, air passes over a very cold evaporator, moisture condenses into droplets, and the air then crosses a warm element before returning to the room, so it comes back drier and slightly warmer. A desiccant model, by contrast, relies on an absorbent material; the British manufacturer Meaco rates its DD8L Pro for operation between 1°C and 35°C, aimed squarely at cold rooms.
That temperature gap matters more than any spec sheet headline. A January bedroom in an inland house, sitting at just a few degrees, is nothing like the test chamber in which rated capacity is measured.
Reading the litres-per-day figure without being misled
Declared capacity is the volume of water extracted in 24 hours under specific conditions, almost always 30°C and 80% humidity. In a real home the figure will be lower. Manufacturer data illustrates the point: the Midea DM20 is rated at 20 litres per day at 30°C/80% with 360W of power, while the Deye DYD-M35A claims 35 litres per day under the same conditions but only 21 litres at 27°C and 60%, drawing 370W either way.
The Meaco DD8L Pro, a desiccant unit at maximum speed, is listed at 7.97 litres per day at 20°C/60% using 623W, and 6.89 litres at 10°C/60% using 630W. Comparing a compressor’s box figure with a desiccant’s is therefore comparing apples with oranges.
For sizing, OCU suggests under 16 litres per day for rooms of 20 to 25 square metres and between 16 and 21 litres per day for 35 to 40 square metres. Buyers should also check tank capacity, ideally enough for a full day of water, since tanks typically fill in 8 to 12 hours; continuous drainage options; and a digital hygrostat that switches the unit off once the target humidity is reached. Manufacturers often ask for at least 50cm of clearance around the appliance.
What it adds to the electricity bill
The arithmetic is power multiplied by hours. The Midea DM20 at 360W consumes 0.36 kWh per hour at full output, or 2.88 kWh over eight hours. The Meaco desiccant at maximum speed, the 623W associated with its 7.97-litre rating, uses roughly 5 kWh over the same period; lower speeds draw less but extract less water too. Multiply by the price per kWh on the bill.
Two factors push the real figure down. With a hygrostat, the unit stops once the target is met and does not run eight hours straight. And timing matters: on a time-of-use tariff, running the appliance during cheap hours changes the outcome more than choosing one model over another. For context, consumer calculators put a dehumidifier’s typical annual consumption at around 294 kWh, roughly 53 euros at 0.18 euros per kWh.
On the comfort question, OCU is clear that dehumidifiers do not change the objective temperature of a home, only its humidity, though humidity does shape how cold we perceive a room to be, with dry environments generally feeling more tolerable. Compressor units, as noted, return air slightly warmer.
The broader lesson is that dehumidifiers are too often sold as a substitute for heating or as a cure for mould, and they are neither. They are a tool for bringing a specific room down to the 40–60% range that regulations recommend, and they work well when the type matches the climate. In a cold, damp home in winter, the box’s litres figure deserves scepticism; the low-temperature number is the one that matters, and a manufacturer that does not publish it is telling you something.