Article #1594 - REScheck 2006 IECC Frequently Asked Questions
REScheck
™ versions 4.0.0 and above provide support for IECC 2006. This article provides answers to frequently asked questions regarding the changes to the REScheck software and the 2006 IECC.
My REScheck project complied with the 2003 IECC. Why does it fail under the 2006 IECC?
The 2006 IECC has been completely redesigned, and several of the new code characteristics may cause your house to fail. The most important difference between earlier editions and the new edition is that the 2006 IECC envelope requirements are not coupled to the home's glazing area percentage. A home with modest glazing area, say 13% of floor area, will likely require a more efficient envelope for 2006 IECC compliance. Conversely, a home with larger glazing area, say 20% of floor area, may achieve 2006 IECC compliance with less insulation.
The 2006 IECC also implements a new climate zone system. The new system introduces more homogeneity across climates, resulting in less variation in the envelope requirements from location to location. Therefore, some locations have slightly different (higher or lower) efficiency requirements under the 2006 IECC than under the previous codes.
I have entered high-efficiency mechanical equipment for a tradeoff, but the REScheck compliance index for the 2006 IECC does not change. Why?
The most likely reason is that your home has a better compliance index under the envelope U-factor times the Area (UA) compliance path than under the performance path. If you use high-efficiency equipment and your house fails under the UA path, then REScheck evaluates your house's 2006 IECC compliance under the rules of the performance path. This is a different REScheck mechanism for determining the mechanical equipment tradeoff than used for older codes. However, as for the older versions of the code, the mechanical tab in the software is still optional. If you are already meeting the energy code requirements, you do not need to enter any information about your HVAC system.
Because the new mechanical tradeoff (performance path) takes into account many home features that are not considered in the envelope UA path (e.g., glazing SHGC, orientation, and window-to-floor-area ratio), switching to the performance calculations doesn't always improve compliance, even if high-efficiency equipment is specified. If your window-to-floor-area ratio is greater than 18%, your home is poorly oriented with respect to solar gains, or the glazing properties do not meet the prescriptive requirements, then it is very unlikely that improvements to the HVAC equipment efficiency will result in enough improvement to give a compliance index better than under the UA path. In the UA path, those detrimental house features are ignored.
How does REScheck determine compliance when multiple heating or multiple cooling equipment is used?
REScheck 2006 IECC cannot be used to demonstrate compliance with multiple HVAC systems. When more than one system is defined, REScheck will use the envelope UA approach to determine compliance and will ignore the efficiencies of the equipment. This change was implemented because high-efficiency equipment tradeoffs, which use the simulated performance compliance approach in REScheck for the 2006 IECC, are available only for single systems. Homes with multiple systems or other advanced house features will require a different compliance tool that implements all the features of full-performance compliance. (REScheck is a "limited scope" tool as permitted in the 2006 IECC, Section 404.6.2.)
Why is there a message "invalid conditioned floor area" and what does this mean?
The conditioned floor area is a new input in the project tab of REScheck. Enter the total conditioned floor area of all conditioned floors in the house. Interior floors between two conditioned spaces should not be entered in the Envelope tab.
PNNL-SA-53715