Two things are true at once in winter, and they pull in opposite directions. Cold air holds very little moisture, so outdoor air is genuinely dry — but the moment it enters a heated house it warms up, its relative humidity collapses, and a house that is well sealed traps everything the occupants add. Meanwhile the machine you would use to fix that is fighting temperatures it was not designed for.
So the answer is conditional. Below roughly 65°F a standard refrigerant dehumidifier starts to ice up. Below 41°F most stop being useful at all.
Why cold breaks a refrigerant dehumidifier
A refrigerant unit works by holding a coil below the dew point of the air passing over it. In a warm room that coil might sit at 40°F and water runs off it happily. In a 50°F garage the same coil has to go below freezing to stay below the dew point — so the condensate freezes on the fins instead of draining.
Once ice forms, it blocks airflow, which makes the coil colder, which makes more ice. The unit runs, draws power and collects nothing. Our guide to why dehumidifiers freeze up covers the failure mode and how to thaw one safely.
| Room temperature | Standard refrigerant unit | Unit with auto-defrost | Desiccant unit |
|---|---|---|---|
| Above 70°F | Full output | Full output | Works, but overkill |
| 65–70°F | Good | Good | Good |
| 55–65°F | Reduced, may frost | Good | Good |
| 41–55°F | Ices up, little output | Cycles often, reduced output | Good — the right tool |
| Below 41°F | Effectively stops | Marginal | Still working |
| Below freezing | Do not run | Do not run | Works down to about 34°F |
What still needs drying in winter
Plenty, as it turns out. These are the winter jobs worth running a machine for:
- Condensation on windows and cold walls. The classic winter symptom, and the one people most often misread as a window fault. See condensation on windows for the dew point numbers.
- Laundry dried indoors. One load releases 4 to 9 pints into the house, and in winter that is usually the largest single moisture source in the building.
- Heated basements. A basement held at 65°F with damp walls still needs drying, and it is warm enough for a normal unit.
- Crawl spaces. A sealed crawl space runs its own humidity cycle year-round. See crawl space humidity levels.
- Unheated garages, boats, caravans and sheds. This is desiccant territory. Rust and mold do not stop for winter.
- Drying out after a leak. Water damage does not wait for spring.
Desiccant units: the winter machine
A desiccant dehumidifier has no cold coil and no compressor. Air passes through a rotor coated with a moisture-absorbing material, and a heater drives the collected water off the rotor into a collection stream. Nothing has to get below freezing, so nothing ices up.
| Refrigerant | Desiccant | |
|---|---|---|
| Best below 60°F | No | Yes |
| Best above 70°F | Yes | Less efficient |
| Heat added to room | 2–5°F | Up to 10°F+ |
| Typical power draw | 300–700 W | 300–700 W, but constant |
| Noise | Compressor hum | Fan only, generally quieter |
| Weight | Heavier | Lighter, easy to move |
The heat a desiccant adds is a real advantage in a cold garage — it dries and takes the edge off at the same time. In a warm bedroom in summer it is a drawback, which is why they are a seasonal second machine rather than a replacement. Our guide to how dehumidifiers work compares the two mechanisms in detail.
Winter settings
Do not simply carry your summer target across. In winter the constraint is not comfort, it is the temperature of your coldest surface:
- Living space: 40–45%. Lower than the 45–50% you would run in summer, because the glass and exterior walls are much colder.
- Drop to 35–40% in a hard freeze. If it is 0°F outside and you have older double glazing, 45% will condense.
- Heated basement: 50%. Unchanged.
- Unheated space: 50–55% is enough. You are preventing rust and mold, not making it comfortable. Chasing 45% in a garage wastes a lot of electricity.
- Do not go below 30%. Dry air cracks furniture and trim and is unpleasant to breathe. Ideal indoor humidity levels has the full room-by-room table.
Storing one over winter
If you are putting a refrigerant unit away rather than running it, five minutes now saves a machine that will not start in spring:
- Run it for an hour with the bucket out, so the coil and pan dry fully.
- Empty and wash the bucket, then dry it completely. Water left standing is what causes the smell you will meet in April.
- Wash the filter and let it dry before refitting.
- Coil the drain hose and store it separately so it does not kink.
- Store upright. Laying a compressor unit on its side can move oil out of the compressor; if it does get tipped, stand it upright for 24 hours before running it.
- Cover it loosely against dust, somewhere above freezing if you can.
The full year-round schedule is in our dehumidifier maintenance guide.
Common questions
Should I run a dehumidifier in winter at all?
Only if you have a measured problem: condensation, damp smells, or a hygrometer reading above 50%. Many well-ventilated houses drop to 30–35% in winter on their own, and running a dehumidifier into that makes the air uncomfortably dry.
Can I leave one in an unheated garage over winter?
Only a desiccant unit, and only above freezing. A refrigerant unit left in a garage that drops below freezing risks damage to the compressor and cracked drain components, and it will collect nothing anyway.
My dehumidifier collects nothing in winter. Is it broken?
Usually not. Check the room temperature first, then the humidity. Below 65°F output falls sharply, and if the room is genuinely at 40% there is very little water left to take. The nine causes of a unit collecting no water works through this in order.
Does a dehumidifier make a house cheaper to heat?
Marginally, and not enough to justify running one for that reason. Drier air needs slightly less energy to warm, and the unit itself adds heat — but you are paying for that heat at electricity rates. Run it for moisture, and treat the warmth as a small bonus.
The short version
Measure before you run anything. If the space is above 65°F, your normal unit is fine — just lower the target to 40–45%. If it is colder than that, you need a desiccant machine or nothing at all.
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