1. Air-Conditioning, Heating, and Refrigeration Institute (2008a). Industry statistical profile: Gas warm air ventral furnaces by AFUE. Air-Conditioning, Heating, and Refrigeration Institute. http://www.ahrinet.org/Content/Furnaces_609.aspx . Accessed 7 August 2008.
2. Air-Conditioning, Heating, and Refrigeration Institute (2008b). Air-conditioning, heating, and refrigeration shipments data. Air-Conditioning, Heating, and Refrigeration Institute. http://www.ahrinet.org/Content/MonthlyShipmentReports_375.aspx . Accessed 7 August 2008.
3. Ashdown, B. G., Bjornstad, D., Boudreau, G., Lapsa, M., Schexnayder, S., Shumpert, B., et al. (2004). Heat pump water heater technology: Experiences of residential consumers and utilities. Oak Ridge National Laboratory, Report No. ORNL/TM-2004/81. http://www.ornl.gov/∼webworks/cppr/y2005/rpt/120517.pdf . Accessed 7 August 2008.
4. Energy Star (2008). Energy star residential water heaters: Final criteria analysis. http://www.energystar.gov/index.cfm?c=new_specs.water_heaters . Accessed 7 August 2008.
5. Ghent, P., & Keller, C. (1999). A comprehensive review of market research on solar water heaters. National Renewable Energy Laboratory, Berkeley, CA. Report No. NREL/SR-550-27123. http://www.nrel.gov/docs/fy00osti/27123.pdf . Accessed 7 August 2008.