Many older houses in the US are either not well designed from a thermal point of view or have HVAC (Heating Ventilation and Air Conditioning) systems in need of repairs or improvements. The building envelopes tend to have poor insulation and lots of leakage, and the HVAC systems are inefficient. The cooling/heating equipment is often located outside of the conditioned space (e.g. in attics or crawlspaces) with ducts that leak and have poor insulation, which cause energy loss and bad occupant comfort on peak days or in extreme climates. We developed a series of retrofits that will allow us to reduce the energy consumption of residential HVAC systems as well as improve the performance of such systems. A computer simulation tool (Regcap), developed at the Energy Performance of Building Groups was used to investigate the effects on a typical house of improving the ducts, and replacing the cooling/heating equipment and air handler. Additional energy savings through solar control and adding an economizer were also examined.