- Steam or hot water radiators or baseboards
- A distribution system where steam or hot water circulates through cast-iron radiators or base boards. Some other types of equipment in the building may be used to produce the steam or hot water or it may enter the building already heated as part of a district hot water system. Hot water does not include domestic hot water used for cooking and cleaning.U.S. Dept. of Energy, Energy Information Administration's Energy Glossary
Energy terms . 2014.