A humidifier is a device, primarily an electrical appliance, that increases humidity (moisture) in a single room or an entire building. In the home, point-of-use what humidifiers are commonly used to humidify a single room, while whole-house or furnace humidifiers, which connect to a home's HVAC system, provide humidity to the entire house. Medical ventilators often include humidifiers for increased patient comfort. Large humidifiers are used in commercial, institutional, or industrial contexts, often as part of a larger HVAC system. Overview Humidification calculation Humidity per hour: X = Air changes per hour (ACPH) * M³ * density of air * humidity ratio Humidity per day: X * 24 The air changes per hour (ACPH) ranges wildly based on: Ventilation: Values may be obtained from the HVAC maintainer that routinely (typically every third year or so) tests the ventilation of the residence. Insulation leakage: Measured with a standard blower door test. Cubic meters: The volume of the room, excluding the bathroom that should be kept closed since it ventilates humidity. Density of air: Typically 1.2 for dry air. Humidity Current relative humidity: 20% Humidity needed to reach 55%: 35% Humidity ratio for 35%: 0.0051 For example, a typical modern apartment of with closed windows (wood isolation) may consume to raise the relative humidity from 20% to 55%: 24 * 1,53 L/h (2*1×125×1.2×0.0051): Air changes per hour Ventilation: 2 Insulation leakage: 1 (a few windows) Cubic meters: 125 m³ (50 m² * 2.5 m height) Density of air: Typically 1.2 for dry air. Humidity Current relative humidity: 20% Humidity needed to reach 55%: 35% Humidity ratio for 35%: 0.0051 Prevention of low indoor humidity Low humidity may occur in hot, dry desert climates, or indoors in artificially heated spaces. In winter, especially when cold outside air is heated indoors, the humidity may drop to as low as 10–20%. A relative humidity of 30% to 50% is recommended for most homes. Health treatment Prevention of dermatitis: Low humidity can cause adverse health effects and may cause atopic dermatitis, and seborrhoeic dermatitis. Management of hair loss: Commonly, patients with seborrhoeic dermatitis experience mild redness, scaly skin lesions and in some cases hair loss. Prevention of dry mucous membranes and cough: By drying out mucous membranes such as the lining of the nose and throat, it may also lead to a snoring problem, and can cause respiratory distress. Prevention of dry eye syndrome. Improved apparent