As spaces are placed in a project, Revit assigns them to the Default zone. It is recommended that you create HVAC zones to meet the heating and cooling requirements of your project and assign each space to a zone that you have created.
Spaces that remain in the Default zone are not included in heating and cooling loads calculations. This allows you to independently determine the heating and cooling loads of the spaces in each zone to produce a more accurate heating and cooling loads analysis with Systems Analysis.