When investing in new power plants, life-cycle benefits of these plants, particularly in regards to environmental emissions is becoming a growing concern. With a variety of new technologies coming online that can serve power loads, it is key to have the tools available to conduct a full scale life-cycle analysis of different power systems. This paper moves the research forward by providing an improved methodology to compare a traditional natural gas combined cycle plant (NGCC) with a distributed energy resource combined heat and power (CHP) system The goal of this study is to quantify the environmental profile of electricity provided by a 555 MW NGCC power plant compared to 1-20 MW gas turbine-based CHP plants with displaced heat credits, when those systems meet the equivalent power demand of 1 MVVh delivered to the end user. Cradle-to gate life cycle assessment/analysis (LCA) models of NGCC and distributed natural gas fired CHP are developed to compare the life cycle (LC) emissions. This study is based on public national mix data in the U.S., guaranteeing the results are producible. It is an initial attempt to quantify environmental differences between the centralized NGCC system and distributed CHP generation, as our developed LCA methodology overcomes the challenges of coproduct system and scale-up by using fundamental and transferable estimation methods. Hypothetically adjusted "displaced heat" from the CHP is used to calculate emissions credits to the system. Power law and input output model are used to compare between power systems with a large capacity gap, which is from 1 to 555 MW in this study. The calculated emissions of 557 kg CO2e/M-Wh (without displaced heat credits) is verified within the range of previous harmonized review of greenhouse gas (GHG) emissions. Non-GHG (i.e., Hg, Pb, etc.) results highlight emissions resulting from the construction, commissioning/decommissioning of displaced boilers as the key parameters in respect to environmental performance of CHP.