The low energy consumption of new housing, together with low temperature space heating solutions, provides a great deal of potential for an improvement to the thermal and environmental performance of heat-generating technologies and heat loss reduction in heating systems. The objective of this work is to evaluate the performance of a pellet and solar combisystem at different temperature ranges in a space heating (SH) system. The dynamic system simulation was performed in TRNSYS. Four SH temperature ranges will be assessed through different cases. For every SH temperature range, two cases were simulated—with and without an electric auxiliary heater. A system without solar collectors was used for the reference cases. The study will show that in the different cases, the reduction of the SH temperature allows for the reduction of temperature setpoints for the pellet boiler. A higher thermal performance of heat-generating technologies, lower heat losses and lower CO emissions can then be reached as a result. A further reduction of SH temperature will lead to slightly higher solar gains and a lower amount of total CO emissions. At the same time, higher heat losses from some components and lower or similar fractional thermal energy savings were observed.