Overview
EN ISO 11855-3:2021/A1:2023 is a CEN-adopted amendment to ISO 11855-3 and updates guidance for the design and dimensioning of embedded radiant heating and cooling systems (floor, wall and ceiling integrated systems). Approved by CEN in May 2023 and published October/December 2023, this amendment clarifies characteristic curves, thermal-resistance requirements, construction models, and calculation inputs for designers and HVAC professionals. It is part of the ISO 11855 series and is intended for national adoption across CEN members.
Key topics and technical requirements
- Characteristic curves and pipe spacing: The amendment requires the field of characteristic curves for floor heating (constant pipe spacing W) to include curves for surface-covering thermal resistance R = 0, 0.05, 0.10 and 0.15 m·K/W (per ISO 11855‑2). Values R > 0.15 may be applied only if verified.
- Back-side thermal resistance (Rλ,ins): Designs must specify a minimum back-side thermal resistance of the insulating layer in accordance with ISO 11855‑5:2021, clause 5.1.2.3.2 to limit downward heat flow.
- Effective insulation thickness and conductivity: The amendment defines how to calculate effective thickness (s) and effective thermal conductivity (λ) for different system constructions (system types I, II, III, IV), including flat panels, profiled panels, studs and joist-based systems.
- Updated calculation inputs: Formula references are revised (e.g., modified Formula (23) for mass flow calculation). The amendment explicitly specifies the specific heat capacity of water c = 4190 J/(kg·K) for use in these calculations.
- Illustrative models and figures: Several figures (Figures 1–7, Figures A.1) and their keys were updated to illustrate construction layers, pipe spacing, thermal diffusion layers and floor models used in dimensioning.
Applications and users
This amendment is practical for:
- HVAC and building services engineers designing embedded radiant floor, wall or ceiling systems
- Architects and façade/flooring specifiers integrating low-temperature radiant solutions
- Energy consultants and performance modelers needing standardized inputs for heat transfer and flow calculations
- Manufacturers and installers of radiant systems for compliance, product data and installation detailing
- Standards committees and regulators aligning national codes with EN/ISO requirements
Practical uses include calculating pipe spacing and flow rates, specifying insulation layers to avoid unwanted heat loss, and producing performance characteristic curves for design verification.
Related standards
Keywords: EN ISO 11855-3:2021/A1:2023, embedded radiant heating and cooling, design and dimensioning, floor heating, thermal resistance, insulation, pipe spacing, HVAC standards, CEN, ISO.