Overview
EN ISO 11855-1:2021/A1:2023 (CEN adoption of ISO 11855-1:2021/Amd 1:2023) is an amendment to the international standard that defines terminology, symbols and comfort criteria for embedded radiant heating and cooling systems. This update (approved September 2023, published December 2023) clarifies comfort metrics and introduces a formal classification of radiant system types to support consistent design, calculation and performance assessment across floor, wall and ceiling radiant applications.
Key topics and technical requirements
- Definitions and symbols: Standardizes terminology and graphical symbols used for radiant heating and cooling, improving communication between designers, installers and regulators.
- Comfort criteria: Updates criteria for thermal comfort and adds an explicit reference to acoustical comfort in thermo-active building systems (TABS).
- Radiant system classification: Introduces Types I–V based on construction and thermal behaviour:
- Type I - pipes in thermal diffusion layer (pipes embedded in screed)
- Type II - pipes in insulation with thermal conduction layer (sheet metal etc.)
- Type III - capillary tubes in thermal diffusion layer (high tube density)
- Type IV - pipes on insulation with thermal reflection layer and air gap (e.g., sports halls)
- Type V - pipes integrated directly in structural construction (TABS)
These types are described by their main elements (e.g., thermal diffusion layer, conduction layer, insulation, capillary tubes, air gap) and are summarized in Annex C for quick reference.
- Thermal output determination: Specifies when to use calculation methods versus measurement. Calculation methods for each radiant system type are detailed in ISO 11855-2; where boundary conditions fall outside applicability, measurement or detailed numerical methods (finite difference/finite element) are required.
- Design implications: Provides parameters (e.g., screed or insulation thickness, layer locations) that affect thermal performance and are essential for correct dimensioning and control.
Applications
This amendment is directly applicable to professionals designing and specifying embedded radiant heating and cooling systems for buildings:
- HVAC engineers and system designers (floor, wall, ceiling systems)
- Architects and building services consultants integrating radiant systems into building envelopes
- Manufacturers of pipes, capillary mats, conduction sheets and prefabricated radiant elements
- Installers, contractors and commissioning/measurement teams responsible for performance verification
- Facility managers and energy consultants concerned with thermal comfort, acoustic impacts and operational control (TABS)
Related standards
- ISO 11855 series (see ISO 11855-2 for thermal output calculation methods)
- Developed by ISO/TC 205 (Building environment design) in collaboration with CEN/TC 228 (Heating systems and water-based cooling systems in buildings).
This amendment aids consistent, SEO-relevant search terms such as EN ISO 11855-1:2021/A1:2023, embedded radiant heating and cooling systems, radiant system types, thermal output calculation, and thermo-active building systems (TABS).
