Below roughly 10 to 15 °C, most compressor dehumidifiers lose much of their output. For a garage, conservatory, outbuilding or unheated spare room, a desiccant model is usually the safer choice.
Not sure what size you need? Answer a few questions and see the working.
Size my dehumidifierWhy cold is a problem for compressors
A compressor unit cools air so water condenses on a cold coil. In a cold room the coil gets close to freezing, ice can form, and the unit spends more time defrosting than drying. Meaco's rule of thumb is that compressors are only effective in spaces above 10 °C and perform best at 16 °C and above. TechRadar similarly says compressor efficiency drops notably below about 15 °C. Desiccant models use an absorbing wheel, and both sources say they perform much the same whatever the room temperature.
Meaco's rule of thumb
| Room temperature | What Meaco suggests |
|---|---|
| Below 10 °C | Desiccant only |
| 10 to 15 °C | Desiccant, or a large (20 to 25 L) compressor |
| Above 15 °C | Desiccant, or a compressor of any size |
Meaco is a maker of both types, so treat this as one maker's guidance. It also says its larger Arete One models did better than expected at 10 °C in Which? tests.
Check the minimum operating temperature
Every unit has a lowest temperature it is designed for. In our data, the compressor models with a stated figure are rated down to 5 °C and the two desiccant models to 1 °C. An unheated garage in January can be colder than that, in which case none of them is designed to run. Look for the figure on each product page.
Desiccant models we list
| Model | Type | Rated | Rated at | At 20 °C, 60% RH | Max power | Noise | Tank | Min. temp |
|---|---|---|---|---|---|---|---|---|
| EcoAir DD1 Simple MK3 | Desiccant | 7.5 L/day | Not stated | – | 580 W | 34–47 dB | 2 L | 1 °C |
| Meaco DD8L Zambezi | Desiccant | 8.3 L/day | 20 °C, 60% | 8.3 L/day | 661 W | 41–50 dB | 3 L | 1 °C |
The trade-offs
- Running cost. Desiccant units draw more power for the water they remove. Meaco gives about 330 W for a desiccant model at 20 °C and 60% humidity, against 150 to 260 W for compressors. Our table uses each model's listed maximum.
- Warm exhaust. Desiccant air is warmer than room air, by about 10 °C per TechRadar. That is not enough to heat a room but can help dry things.
- Capacity. The desiccant models we list are in the 7.5 to 8.3 litre class. For a very large or very damp space you may need more than one.
- What a dehumidifier cannot do. If the garage or conservatory leaks, fix that first. See when damp isn't a dehumidifier problem.
Sizing it
Use the sizer and choose "cold or unheated". It points you to desiccant or hybrid types. For the full comparison, see compressor vs desiccant.
Sources: Meaco, When to buy a desiccant or a compressor dehumidifier; TechRadar, Desiccant vs compressor dehumidifier. Specifications from each product page.