What do they do?
Dehumidifiers draw water from the air into them. They often contain a type of crystal gel that absorbs water from the air, although industrial ones work a little like ventilator fans and ‘suck’ the water out of the air. Humidifiers release a steady jet of water mist, adding water to the air. They can be steam driven, or produce ‘cool’ mist via ultrasonic technology.
When do I need them?
Dehumidifiers are used to combat mould and damp in spaces that might need them. This can be anything from the roof cavity through to your wardrobe or the bathroom cupboards. They help prevent mildew and keep away the damage that rising damp can do.
Humidifiers are used to increase the moisture load of the environment for human comfort. They can often cut down on sinus discomfort and even the chance of germs spreading. They’re often recommended for babies, and even adults should ideally be living at 30-50% humidity for maximum comfort and skin benefits.
You can [and should] measure your indoor humidity with a hygrometer, as you don’t want to make the air too wet in case you cause mould issues. It is, however, totally possible to need both in your house at once – one to tackle the dingy top of the wardrobe and the other to keep you comfortable in the dry winter season.