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Why apartment bathrooms stay damp
A shower puts a surprising amount of water into the air — a ten-minute hot shower can add a pint or more of moisture to a small bathroom. In a windowless rental bathroom with a weak or absent extractor fan, that moisture has nowhere to go. It condenses on cold tiles, mirrors and the ceiling, and it lingers for hours.
That lingering damp is what grows mould in the grout, the sealant and the corner of the ceiling, and it is what makes the room smell musty. A dehumidifier removes the moisture at the source, which is more effective than wiping surfaces after the fact. Our musty-smell guide and no-exhaust-fan guide cover the wider problem.
In a rental you usually cannot install a proper extractor fan, so a portable dehumidifier is the practical fix. It is also the one you can take with you when you move.
Sizing for a small bathroom
Dehumidifiers are rated in pints per day (or litres per day). For a small bathroom of 40 to 60 square feet, a unit rated for 20 to 30 pints per day is plenty; a larger unit is overkill and noisier. The rating assumes a warm, humid condition, so a small unit handles a small room well.
Look for a humidistat so the unit switches off once the room is dry, rather than running continuously and over-drying. A target of 40–50% relative humidity is right for a bathroom. Our budget dehumidifier guide and small-room dehumidifier picks show the sizing in context.
Do not oversize: a big unit in a tiny bathroom cycles on and off awkwardly and uses more power than you need.
Compressor vs desiccant
Compressor dehumidifiers are the common type: they work best in warm conditions (above about 65 °F) and are efficient in a heated bathroom. Desiccant dehumidifiers work better in cold conditions and are lighter, but use more power. For a heated apartment bathroom, a compressor unit is usually the better buy.
If the bathroom is unheated and cold, a desiccant unit will pull more water. If it is warm, a compressor unit is quieter and cheaper to run. Our basement dehumidifier guide covers the cold-room case in more depth.
Either way, check the noise figure: a bathroom dehumidifier runs while you are in and around the room, so a unit under about 45 dB is much more liveable.
Draining without a floor drain
Most apartment bathrooms have no floor drain, so you have two options: a tank you empty by hand, or a continuous drain hose you can route to the shower, sink or a bucket. A tank is simplest but needs emptying after every few uses; a hose is more convenient if you can route it without a trip hazard.
For a bathroom, a continuous drain into the shower tray is ideal — the water goes where it would have gone anyway. If that is not possible, choose a unit with a large tank and an auto-shutoff so it does not overflow. Our no-drain-hose guide covers the tank-only case.
Never let a hose run uphill or kink; the unit will not drain and will shut off. Keep the hose out of walkways.
Placement and habits
Put the dehumidifier on the floor near the dampest spot, a few inches off the wall so air can circulate. Keep the bathroom door closed while it runs so it is drying the bathroom, not the whole flat. Run it for 30 to 60 minutes after each shower, and longer on wash days when you dry laundry indoors.
Habits matter as much as the machine: squeegee the shower screen, leave the door open to the hallway once the room is dry, and fix any dripping tap or leaking seal. Our after-shower guide and bathroom placement guide cover the routine.
If the bathroom has a window, open it briefly after a shower to flush the humid air, then let the dehumidifier finish the job.
Safety in a wet room
A dehumidifier in a bathroom is an electrical appliance in a wet room, so safety matters. Keep it away from the shower and any standing water, never run it with a damaged cord, and plug it into a socket away from splashes. If the socket is close to the shower, use a different one.
Empty the tank before it is full, and never tip a running unit. Our safety checklist covers the cord and stability points in more detail.
If the room is genuinely flooded, fix that first. A dehumidifier is for routine damp, not for standing water.
Picks by budget
Under $100, a small compressor unit rated 20–30 pints/day with a humidistat and a tank is enough for a bathroom. Around $150 you get a continuous drain option and a quieter fan. Above that you are paying for larger capacity you do not need in a bathroom.
Whatever you buy, confirm the pint rating, a humidistat, and either a large tank or a drain hose. Our budget dehumidifier guide and small-apartment dehumidifier picks are the two lists to compare.
Dehumidifier type vs an apartment bathroom
| Type | Best in | Power use | Bathroom verdict |
|---|---|---|---|
| Compressor | Warm rooms (65°F+) | Lower | Best for heated bathrooms |
| Desiccant | Cold rooms | Higher | Best for unheated bathrooms |
| Mini / peltier | Very small spaces | Low | Only for tiny cabinets |
| Whole-room | Large spaces | High | Overkill for a bathroom |
Sources: U.S. EPA (mould and indoor humidity), AHAM (dehumidifier sizing), ASHRAE (ventilation and humidity), manufacturer dehumidifier specifications.
Frequently asked questions
What size dehumidifier do I need for an apartment bathroom?
Do I need a drain hose for a bathroom dehumidifier?
How long should I run a dehumidifier in a bathroom?
Is a compressor or desiccant dehumidifier better for a bathroom?
Can I leave a dehumidifier running in a bathroom overnight?
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