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Why bedrooms get damp in the first place
Bedrooms are the dampest rooms in most apartments, and it is rarely obvious why. You spend eight hours a night breathing out roughly half a litre of water vapour, the door is usually shut, and in a modern sealed flat there is nowhere for that moisture to go. Add a bathroom next door that vents into the corridor and a mattress that holds whatever humidity the room has, and you have the classic recipe for a musty bedroom.
The tell-tale signs are a cold, clammy feel in the morning, condensation on the window, and a smell that lingers on pillows. If you have already noticed that smell, our guide to getting rid of a moldy smell in an apartment covers the source, and how to reduce humidity in an apartment covers the everyday habits that keep it from coming back.
A dehumidifier is the fix for the room itself, but it works best alongside ventilation. If the bedroom shares a wall with a windowless bathroom, the moisture problem is really a ventilation problem — see our no-ventilation guide before you buy anything.
What size dehumidifier a bedroom needs
Dehumidifier capacity is measured in pints of water removed per 24 hours, and the number you need scales with room size and how damp the room is. A small, mildly damp bedroom needs far less than a cold, dripping one. The table below is the honest starting point for a rental bedroom.
Two rules save money here. First, do not oversize for a bedroom: a big unit cycling on and off is louder and more expensive than a correctly sized one running steadily. Second, if you are between two sizes, go up one step — a larger unit at low speed is quieter than a small unit at full tilt. Our pints calculator walks through the arithmetic, and sizing for a small bathroom shows the same logic applied to a wetter room.
Noise: the number that actually decides it
You will run a bedroom dehumidifier at night, so noise is not a nice-to-have — it is the deciding spec. Compressor dehumidifiers hum and click; desiccant units are quieter but use more power and work better in cold rooms. For a bedroom, a compressor unit rated around 38–42 dB on its low setting is the practical target.
Ignore the single “as quiet as” figure and look for a full noise table. If the brand only quotes one number, assume it is the lowest speed with almost no airflow. Our comparison of desiccant vs compressor dehumidifiers explains which type suits a cold bedroom, and the small-apartment shortlist lists the low-speed dB next to each pick.
Where to put it in a small room
Placement changes both how well it dries and how loud it sounds. Put the unit on the floor in the middle of the room's airflow, not jammed into a corner where the intake chuffs against a wall. Keep it at least 20 cm from any surface, and leave the bedroom door ajar so it can pull damp air from the rest of the flat.
Do not put it on a hollow nightstand or a wooden floor if you can avoid it — both amplify the compressor hum. A rug or a folded towel underneath cuts the vibration noticeably. The same placement logic is covered in more detail in our bathroom placement guide.
Draining it without drilling
Every dehumidifier has a tank, and in a bedroom you will empty it more often than you expect — a 20-pint unit in a damp room can fill a 2-litre tank in a night. The renter-friendly answer is a continuous-drain hose that runs to a nearby drain or a larger container, so you never have to wake up to a full tank.
You do not need to drill anything. A gravity hose laid along the skirting board to a shower or a bucket works fine, and most units ship with the port. Our continuous-drain setup guide shows the no-drill version, and units that work without a hose covers the tank-only options if a hose is not practical.
What it costs to run
A 20–30 pint compressor dehumidifier draws roughly 300–450 W, so running it eight hours a night costs a few cents to a few tens of cents a day depending on your electricity rate. That is cheap next to the cost of replacing a mouldy mattress, but it is not free, and a badly sized unit that runs constantly will show up on the bill.
Run it on a timer or a target-humidity setting rather than 24/7. Once the room is at 45–50% relative humidity, the unit should cycle off. Our running-cost breakdown does the monthly maths, and what humidity to set it to tells you where to point the dial.
Picks by budget
At the budget end, a basic 20-pint compressor unit with a mechanical humidistat is enough for a small bedroom and easy to replace if it dies. Mid-range adds a digital humidistat, a continuous-drain port and a quieter low speed — worth it if you will sleep beside it. Above that you are paying for app control and larger tanks, which matter more in a basement than a bedroom.
If your bedroom is genuinely cold and damp, a desiccant unit is the better tool even though it costs more to run. For a damp basement bedroom, see the basement picks, and for a lease-friendly all-rounder, renter-friendly dehumidifiers is the shortlist.
Bedroom dehumidifier capacity by room size
| Room size | Damp level | Capacity (pints/24h) | Notes |
|---|---|---|---|
| Up to 100 sq ft | Mild | 10–20 | Tank-only is fine |
| 100–150 sq ft | Moderate | 20–30 | Sweet spot for a bedroom |
| 150–250 sq ft | Moderate | 30–40 | Look for a quiet low speed |
| Any size | Very damp / cold | Desiccant unit | Better below 15°C |
Sources: U.S. EPA (A Brief Guide to Mold, Moisture and Your Home), ASHRAE Standard 62.2 (ventilation), AHAM dehumidifier capacity ratings, U.S. DOE energy-use guidance.
Frequently asked questions
How many pints do I need for a bedroom?
Can I leave a dehumidifier on all night?
Are dehumidifiers loud at night?
Do I need to drill to drain it?
Will a dehumidifier stop condensation on my window?
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