This research focused on studies of the cross-laminated timber (CLT) construction system and, in particular, on an innovative panel composition of eucalyptus (Eucalyptus grandis) heartwood, which is considered in Brazil as a low-added-value material that is often discarded or used for less noble purposes. The aim of this study was to investigate the thermo-energetic performance of CLT panels for use in low-income housing under several different climate conditions. The research was based on the simulation method of the Brazilian Technical Regulation of Quality for the Energy Efficiency Level of Residential Buildings (RTQ-R). The results, based on 72 parametric simulations, proved that CLT panels made of eucalyptus heartwood have significant potential for thermo-energetic improvement in various housing types under diverse climatic conditions. The simulated envelope combinations showed that in Curitiba (bioclimatic zone 1), it is important to associate 5-layered CLT panels with 10 cm thermal insulation; in São Paulo (bioclimatic zone 3), the envelope should be provided with low solar absorptance and 5-layered CLT panels without thermal insulation; and in Belém (bioclimatic zone 8), in addition to the low solar absorptance in the envelope, the CLT panels should be composed of only three layers and without thermal insulation. It was concluded that the innovative CLT construction system with low-added-value eucalyptus heartwood is a very promising technology for Brazilian dwellings that are more energy efficient, with further studies on mechanical behavior being necessary for its consolidation in the country.