# Chiller

> A chiller is a refrigeration unit that cools hydroponic nutrient solution, keeping it around 18-21 °C so it holds more oxygen and root pathogens are discouraged.

- Canonical: https://genetixbay.com/knowledge/glossary/chiller.html
- Also written: water chiller, reservoir chiller, aquarium chiller, res chiller, inline chiller
- Glossary category: Systems and media · 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 chiller is a compressor-based refrigeration unit, like a small air conditioner for water, that pulls heat out of a reservoir. Solution is pumped through the chiller's heat exchanger and back, or a coil is placed in the tank. Units are rated by cooling capacity (watts, BTU/h or horsepower fractions) and by the volume they can handle.

## In practice

Chillers matter most in [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md) and [aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md), where roots live in solution. Cool water holds more dissolved oxygen, and warm solution above roughly 22-24 °C (72-75 °F) is strongly linked to *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md). Size the chiller for the room's heat, not just the reservoir volume: lights, pumps and warm air all add heat. Place the unit where it can [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) its own heat outside the grow, and insulate lines and buckets.

Frozen water bottles are a short-term emergency fix, not a substitute.

## Don't confuse with

- **Air conditioner**: cools air; may help, but solution can still warm from pumps and lights.
- **Heat exchanger coil**: one part of a chiller setup.

## Related terms

[Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md)

## Read more

- [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md)
- [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)

## Sources

1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/
2. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/