The use of Unglazed Transpired Solar Collectors (UTSCs) is considered to be one of the most effective methods of reducing HVAC loads in buildings. The operation of the UTSC is relatively simple. A perforated absorber plate is installed in a location where it is exposed to solar radiation. Air is drawn through the perforations, and into the fresh air intake of an HVAC system. This pre-warmed air could make a significant contribution towards decreasing the energy used for heating. Unfortunately, commercially available UTSC products are no longer geometrically similar to the products used to produce correlations used by designers for estimating heat loss and effectiveness. The intent of the current investigation, therefore, is to numerically investigate modern UTSC system performance. Numerical development was successful, and the model was validated by comparison to existing experiments and correlations. An experimental investigation, however, is still required to provide formal validation. Correlations for heat loss and effectiveness have been developed. (C) 2013 Elsevier Ltd. All rights reserved.