These two machines are not variations on a theme. They do exactly opposite jobs.
One adds water to the air. The other takes it out.
Buy the wrong one and you will spend six months making the problem you started with measurably worse.
The good news is that a single cheap instrument settles the argument.
A ยฃ10 hygrometer decides this, not a symptom
Relative humidity is what both machines are actually adjusting, and it is the only evidence worth acting on.
The comfortable band for a home is 40 to 60 per cent.
Below 30 per cent, throats and sinuses dry out overnight and static builds up.
Above 60 per cent, dust mites breed happily and mould starts finding cold corners.
A basic digital hygrometer costs about ยฃ10 and reads in seconds. Put one in the bedroom for two nights before buying anything.
The comfort band runs from 40 to 60 per cent. British bedrooms in winter routinely sit above it.
Condensation on the glass means you need the dehumidifier
Walk to the window on a cold January morning and look at the bottom of the pane.
Beads of water there are the clearest signal a British home gives you.
Our housing stock is draught-proofed at the windows but rarely ventilated deliberately, so moisture from cooking, washing and breathing has nowhere to go.
Four people asleep in a closed house put several litres of water into the air every night.
That is why the winter complaint here is damp, black spots behind the wardrobe and clothes that never quite dry.
A humidifier running in a house already sitting at 68 per cent is not treating dryness. It is feeding the mould.
Dehumidifiers are rated in litres extracted per day, and 10 to 12 litres covers a typical three-bedroom house.
There are two mechanisms and the difference matters in an unheated British room.
Compressor models are cheaper to run but lose efficiency below roughly 15ยฐC.
Desiccant models keep working in a cold garage, conservatory or spare room, and run a little warmer and noisier.
A 200W unit running for eight hours uses about 1.6 kWh, which is well under a pound at capped electricity rates.
Bottom line: if the windows stream in winter, a humidifier will not fix a dry throat. It will add to a moisture load the walls already cannot cope with.
Damp and mould, and how they affect healthOfficial NHS guidance โ
The humidifier case is narrower, and heating-driven
There is a real case for the other machine, and it is a specific one.
Central heating in a well-sealed modern flat can pull a room under 35 per cent during a hard frost.
Nosebleeds, a dry cough that clears by mid-morning, cracked lips and constant static are what that feels like.
Nurseries and bedrooms are where it is worth correcting, because that is where you breathe the same air for eight hours.
If you buy one, get a model with a built-in humidistat so it stops at a set level instead of running blind.
In hard-water areas use distilled or filtered water, or the minerals settle as fine white dust โ see our Levoit Classic 300S review: the 5 numbers that decide it.
Tanks also need emptying and rinsing every couple of days, without exception.
A neglected humidifier tank is a warm reservoir, and it will happily distribute whatever grows in it.
Ventilation is free and usually comes first
Before either machine, open two windows on opposite sides of the house for ten minutes each morning.
Cross-ventilation exchanges the moist air faster than any appliance and costs nothing but a little heat.
Run the extractor fan for a quarter of an hour after a shower rather than switching it off with the light.
Dry washing outdoors when you can, and never over a radiator in a closed room.
These habits shift a borderline 62 per cent reading back into the band on their own.
The appliance is for the homes where they are not enough.
