Draft Proposal CB-19 

This concept has been developed by the DOE Building Energy Codes Program (BECP) as a possible code

change proposal to the Commercial provisions of the 2012 International Energy Conservation Code

(IECC).   Interested parties are asked to submit any and all comments on DOE's initial concepts and draft

code change proposals. For instructions on submitting comments, visit:

www.energycodes.gov/development/commercial/codes/iecc/concepts/

Radiant Heating Panel Insulation (CB-19) 

Objective:  Clarify that panels installed in building thermal envelope assemblies must be insulated in

accordance with the requirements of the assembly in which they are installed.  Require insulation of R‐

3.5 on the non‐radiant surface when installed in interior assemblies and refer to the other applicable

sections of the code for heated slab insulation.

Suggested Code Change Proposal

Add a new definition to Section C202 as follows:

RADIANT HEATING SYSTEM: a heating system that transfers heat to objects and surfaces within the 

heated space primarily (greater than 50%) by infrared radiation.

Revise Section C402.2.8 as follows:

C402.2.8 Insulation of radiant heating systems. Radiant heating system panels, and their associated 

components U-bends and headers, designed for sensible heating of an indoor space through heat transfer 

from the thermally effective panel surfaces to the occupants or indoor space or thermal radiation and 

natural convection and the bottom surfaces of floor structures incorporating radiant heating that are 

installed in interior or exterior assemblies shall be insulated with a minimum of R-3.5 (0.62 m2/K × W) on 

all surfaces not facing the heated space. Radiant heating system panels that are installed in the building 

thermal envelope shall be separated from the exterior of the building or unconditioned or exempt spaces 

by at least the same R-value of insulation installed in the opaque assembly in which they are installed or 

the assembly shall meet the provisions of C402.1.2. 

Exception: Heated slabs on grade insulated in accordance with C402.2.6.

Reason: Clarification of language.  In training sessions it regularly comes up that the current provision

conflicts with an R‐5 requirement in the IMC and the slab insulation requirements for heated slabs.  The

exception addresses this issue.  Beyond heated slabs on grade, what remains are such systems and

panels located in the building thermal envelope or in interior assemblies.  The change also clears up an

interpretation issue.  On the one hand, the current language can be interpreted to allow only R‐3.5 on
the back of a radiant panel installed in an exterior wall.  On the other hand, the section could be

interpreted to mean the radiant panel requires a minimum of R‐3.5 no matter where installed, but does

not relieve the requirement to provide full insulation in an opaque wall assembly.  The proposed

language makes it clear that the full insulation is required in the opaque wall.  The intent of the building

thermal envelope provisions is to minimize the heating loads on the building.  It is not appropriate to

reduce the required amount of insulation in an envelope assembly at the very location of such a heating

system that introduces a higher temperature difference.  In interior assemblies, the effectiveness of the

radiant heating system is improved if heat loss to interior plenums or wall cavities is reduced.    If the

radiant system/panels cannot be located on an interior assembly and the satisfaction of the insulation

level in the remainder of the assembly is challenging, then the option remains to use C402.1.2.  The

lengthy definitions of radiant heat embedded in the section are removed and a definition matching

ASHRAE 90.1‐2010 for radiant heating systems is added to the IECC definitions.

Cost Impact:   If the current section is interpreted to require minimum insulation on radiant panels but

not reduce any requirement for exterior wall insulation there will be no cost impact.  Based on the

interpretation that only R‐3.5 is required for a radiant panel in an exterior wall, there may be a cost

impact if the designer chooses to install such systems in building thermal envelope assemblies as

opposed to other available assemblies.  Additional cost could be incurred providing full insulation if

above the level of the currently required R‐3.5.   Where heaters are installed in exterior ceilings under

an attic, there is very minimal additional cost to maintain the full attic insulation depth over the radiant

panel.   In actual practice, exterior wall installation is rare, as radiant heaters on the perimeter are

typically installed inside the interior wall finish.  When installed in building thermal envelope assemblies,

there is no reason why they should not be insulated to the same level as the remainder of the envelope

assembly, as the required level of insulation has been previously shown to be cost effective for normal

building thermal envelope conditions.  Insulation adjacent to radiant panels will have a shorter payback

due to the high temperature of the radiant panel compared to the space temperature increasing the

heat loss through the insulation; hence, any additional insulation will be cost effective.