TS EN ISO 7345

TS EN ISO 7345 is a terminology standard that defines the basic physical quantities used when describing the thermal performance of buildings and building components. Standards of this type create a shared technical language so that calculations, test reports, and product information in heat transfer and thermal insulation can be understood in the same way.

How quantities, symbols and units are aligned

The scope of this document is to define the physical quantities used for buildings and building elements, together with the corresponding symbols and units. In practice, that means providing a consistent naming framework for concepts such as heat flow, thermal resistance, thermal conductivity, and temperature difference. This consistency supports engineering calculations, technical reporting, and comparison of data across documents and disciplines.

In general technical terms, thermal performance is about how a building transfers, retains, or loses heat. The subject extends beyond insulation products to the wider building envelope, including walls, roofs, floors, windows, and related components. Clear definitions of symbols and units reduce ambiguity and make technical information easier to compare and apply.

• Organises the basic quantities used to describe thermal behaviour in buildings.
• Aligns the symbols and units associated with each quantity.
• Provides common terminology for heat transfer and insulation-related building elements.
• Supports consistent technical documentation and calculation practice.