Hydronics is the term describing the use of water as a heat-transfer medium in heating systems, and a cooling-transfer medium in cooling systems.

Types of hydronic systems:
- heated water
- chilled water
- steam

Hydronic systems may further be classified by factors such as:
- Flow (forced/gravity)
- Temperature (low/high)
- Pressure (low/high)
- Piping arrangement (e.g. 1- or 2-pipe system)
- Pumping arrangement