# Humidifier

> A humidifier adds water vapour to the air to raise relative humidity, used mostly for clones, seedlings and veg, or dry climates.

- Canonical: https://genetixbay.com/knowledge/glossary/humidifier.html
- Also written: humidifiers, ultrasonic humidifier, evaporative humidifier, mister, fogger
- Glossary category: Environment and light · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A humidifier raises humidity by adding water to the air. Ultrasonic units vibrate water into a fine mist that evaporates; evaporative units pass air over a wet wick; steam units boil water. Each evaporating litre also cools the air slightly, because evaporation absorbs heat.

## In practice

Humidifiers matter most early on: clones like about 70–85% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and early veg 60–70%, which can be hard to hold in dry winter air or under strong [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md). Put the unit on a humidistat or controller and keep it out of the direct line of the canopy so droplets do not settle on leaves.

Ultrasonic humidifiers spray out whatever is dissolved in the water. With [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), that means white mineral dust on leaves, fans and fixtures. Use [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or distilled water in ultrasonics. Clean the tank weekly; stagnant water grows bacteria and fungi that get misted straight into the room.

In flower, needing a humidifier usually means the exhaust is running too hard or the room is [too hot](https://genetixbay.com/knowledge/glossary/heat-stress.md); adjust those first.

## Don't confuse with

- **Dehumidifier**: does the opposite.
- **Fogponics fogger**: mists nutrient solution onto roots, a growing system rather than room humidification.

## Related terms

[Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md)

## Read more

- [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md)