Unheated means without warmth added by a heating system or artificial heat source. An unheated garage stays as cold as the outdoor air in winter because it has no furnace or heaters to warm it. An unheated swimming pool relies only on sunshine to warm the water, which means it might feel quite chilly on cloudy days or in early spring.

The word usually describes buildings, rooms, or spaces where you might expect heat but don't have it. A family might store holiday decorations in an unheated attic, or keep a workshop in an unheated basement where they need to wear jackets in winter. Some older homes have unheated back porches that are comfortable in summer but too cold to use when temperatures drop.

People sometimes choose to leave spaces unheated to save money on heating bills, especially for rooms they rarely use. Other times, buildings are unheated because adding heating systems would be too expensive or complicated. An unheated greenhouse might work fine in mild climates but struggle to protect tender plants when frost arrives.