A humidifier is a household appliance that increases humidity (moisture) in a single room or in the entire home. There are point of use humidifiers, which are commonly used to humidify a single room, and whole house or furnace humidifiers, which connect to a home's HVAC system to provide humidity to the entire house.
Humidification is often necessary in colder climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity.
An air purifier is a device which removes contaminants from air. Air purifies are commonly marketed as being particularly beneficial to allergy sufferers and asthmatics and at reducing second-hand tobacco smoke.
Dust, pollen, pet dander, mold spores, dust mite feces can act as allergens, triggering allergies in sensitive people. Smoke particles and volatile organic compounds (VOCs) can pose a risk to health. Air purifiers are used to reduce the concentration of these airborne contaminants and are especially useful for people who suffer from allergies and asthma. They also reduce the need for frequent household cleaning. Air purifiers use a small amount of electrical energy, causing some expense and environmental effect.