More than 200,000 homes are factory built in the United States each year to the federally preemptive Manufactured Housing Construction and Safety Standards, mandated by the U.S. Department of Housing and Urban Development (HUD). This paper analyzes national energy use and savings potential from improvements to thermal distribution system efficiency, thermal envelopes, and heating, ventilation and air conditioning (HVAC) equipment over what is currently required by HUD code. Estimated energy savings over current HUD code are provided for four cases: National Fire Protection Association Standard 501-2005, the 2006 International Energy Conservation Code, the U.S. Environmental Protection Agency’s ENERGY STAR manufactured housing guidelines , and Best Practice, based on the U.S. Department of Energy’s Building America Industrialized Housing Partnership program home built in the Pacific Northwest. Savings estimates are also provided from improved HVAC system efficiencies, such as using ENERGY STAR heat pumps in lieu of electric furnaces and ENERGY STAR air conditioners. Energy use and associated savings are provided in terms of both energy cost and source energy.