A transition is occurring from DOE-2 to EnergyPlus in verification of residential energy code compliance. which increased the interest in the differences between these simulation tools. This study quantifies the differences between the slab-on-grade heat transfer models of DOE-2 (Winkelmann model, GCW) and EnergyPlus (the Slab model, GCS) programs for low rise energy code compliant residential buildings in hot-humid, hot-dry, temperate and cold climates of the U.S. The reliabilities of these models were also discussed by comparing them with the more detailed TRNSYS slab-on-grade model (GCT). The findings showed that. GCW calculated 10-13% higher total building loads than GCT did for identical slab-on-grade houses. GCS showed unconverged zone air temperatures and limitations for certain insulation configurations which resulted in 18-32% lower thermal loads than those calculated by GCT. When the zone air temperatures were converged, however, GCS calculated building loads within 9% of those calculated by GCT. This indicated a necessity of improvement in GCS to avoid erroneous results in residential energy code compliance calculations. (C) 2012 Elsevier B.V. All rights reserved.