Dehumidifier for a bathroom

That is the whole recommendation for perhaps four bathrooms in five, and there is nothing in it for us to sell you. Below, the arithmetic that makes the case, the four situations where a dehumidifier genuinely is the right answer, and what to look at when you are in one of them — which is not capacity.

A bathroom’s moisture arrives in a burst. Ten minutes of hot water, and the room goes from ordinary to saturated. Everything a dehumidifier does happens after that burst, at a rate set by its rating — so the useful question is how much water a real unit can actually take out during the shower itself.

Most bathrooms that “need a dehumidifier” have a fan that is not doing anything. Five minutes of checking settles it.

1. No window, no fan, and no way to add one. This is the strongest case by a distance, and it is common: an internal bathroom in an apartment block, a rented flat where you cannot cut a duct through a masonry wall, a listed or leasehold building where the freeholder will not permit a new external vent. If ventilation is genuinely unavailable, a portable dehumidifier is the only tool left that removes water rather than moving it around. Run it after showers with the door shut, and it will hold the room out of the mould-risk band between events.

2. A fan that vents into the loft. This one deserves care. A dehumidifier here is a stopgap, not a fix. The real damage is happening above your ceiling — sodden insulation, corroding fixings, mould on the underside of the roof deck — and no amount of drying the bathroom addresses it. Get the duct run to an external terminal. A dehumidifier is a reasonable thing to run in the meantime, particularly through a winter, and a bad thing to accept permanently.

3. Persistent damp hours after the fan has run. If the room is still damp long after the shower, with a fan that demonstrably works, the shower is not the source. Something else is wet — a slow leak behind tiling, an uninsulated cold-water run, or simply a whole floor of the house sitting high. In that case, size for the floor rather than the bathroom, and read the sizing table below with the larger area in mind.

4. Drying laundry indoors. The largest routine moisture load most homes have, and the one people most often solve by hanging a rack in the bathroom and shutting the door. Our own sizing table puts “laundry drying indoors” in its most severe dampness class, alongside standing water — that is how significant it is. Here a dehumidifier is not a substitute for ventilation, it is the correct tool: it dries the laundry faster and takes the water out of the house instead of leaving it in the fabric of the building.

Almost every buying guide in this category tells you to work out how many pints per day you need. For a bathroom that advice is close to meaningless, because the answer is smaller than anything you can buy.

Read the gap. A bathroom in the worst condition our table recognises works out at 11 pints/day, and even a whole 900 sq ft floor with laundry drying on it comes to 14 pints/day. The smallest compressor unit in our data is 50 pints/day — several times either figure.

So do not shop on pints here. Any home dehumidifier will exceed the requirement, and paying up for capacity buys you nothing in a room this size. Shop on the things that actually bite: footprint, tank size, noise, heat and whether it can drain continuously.

One honest limit on that table. Our product data starts at 50 pints/day; we hold no data on the small thermoelectric “mini dehumidifiers” sold specifically for bathrooms and wardrobes. Those are typically rated in ounces per day rather than pints, which is not a DOE-tested figure and not comparable to anything on this page. We have not evaluated them and will not guess.

Relative humidity does not decide whether a surface is wet. The dew point does — the temperature at which the air in the room has to give up its water. Anything colder than that number is running, and stays running until either the air dries or the surface warms.

At 63.5°F the mirror, the window glass and any tiled wall backing onto the outside of the building are all colder than the air’s dew point, so they stream. This is exactly the moment a dehumidifier is too late: the water is already liquid, already on the surfaces, and already wicking into the grout. Extracting the air afterwards makes the room dry out eventually. Extracting the air during means it never gets there.

Between events, the target for the room is the ordinary one: 30–50% RH, and reliably below 60%, which is where sustained mould growth becomes possible. A bathroom is allowed to spike; what it is not allowed to do is sit high all day.

Electrical safety and where you can actually plug it in. US bathroom receptacles must be GFCI-protected, and plenty of older bathrooms have no receptacle at all. Never run an extension lead across a wet floor, and never site a unit where it can be reached from inside the bath or shower or where it will take direct splash. If the only outlet is on the landing, then the machine lives on the landing with the bathroom door open — which changes what you are drying, and means the landing is the space you should be sizing for.

Placement. These machines pull air in one face and blow it out another, and they need clearance on both. Manufacturers generally specify several inches all round; check the manual for the unit you buy, because we have not run them. A dehumidifier wedged behind a door in a corner recirculates its own dry exhaust and reads as a broken machine.

Tanks are the real limit, not capacity. Compact units carry small tanks, and a full tank shuts the machine off. A dehumidifier that stopped at two in the morning did nothing overnight, which is when you needed it. Continuous drainage fixes this permanently, and it is the single feature worth insisting on — but check that the fitting is a genuine gravity drain and that you have somewhere below the outlet for the hose to run to. Most bathrooms do not, which is why the tank ends up mattering more here than in a basement.

Heat. A refrigerant dehumidifier is a heat pump that dumps its waste heat into the room it is standing in. In a space this small you will feel it, and in summer that is a genuine comfort cost.

Noise. A compressor and a fan in a fully tiled room, with no soft surfaces at all, is louder than the same machine anywhere else in the house.

One recommendation, not a list, because the sizing table above has already established that the capacity question does not discriminate between units here. On our own data the sensible pick is the smallest tested capacity available, at the lowest price with a review count large enough to be worth anything, and with a drain fitting so the tank stops being the limiting factor.

It is not a small machine and it was not designed for a bathroom — nothing in our data was. If your case is number two, the fan ducted into the loft, buy the ductwork before you buy this.

The one exception on capacity. If your case is drying laundry, and you are drying it for a household rather than the occasional rack, you are running the machine for hours at a time across more than one room. That is the only version of this problem where a larger unit earns its price — not because the pints are needed, but because a bigger machine reaches the target faster and then cycles, rather than running flat out all evening.

We have never run either of these units, in a bathroom or anywhere else, and we have never measured a shower. What we publish instead is the arithmetic, on both rating scales, so you can check it: the removal rates are the manufacturers’ own DOE figures divided by the clock, the sizing figures are the standard dampness classes converted onto the modern scale, and the dew point is the Magnus formula.

We also do not quote the square-footage coverage claims printed on these boxes. In our own product data, three units all rated 155 pints per day advertise 7,500, 6,000 and 6,000 square feet, and a 160-pint unit advertises 2,500. There is no standard behind the number, so it cannot be compared between brands.

And the conclusion has not changed for having read this far: if you can get a fan working and venting outdoors, do that instead. The rest of our buying guides are for spaces where the moisture has nowhere else to go.