According to ENERGY STAR®, the most cost-effective way to increase your home's energy efficiency is to improve the "envelope," which consists of outer walls, ceiling, windows and floors.
Most do-it-yourselfers can seal air leaks. Just seal holes around doors and windows with caulk or weather stripping.
ENERGY STAR reports that about 20% of the air that moves through the cooling system ducts in a typical house is lost due to leaks and poorly sealed connections. This loss results in higher energy use, no matter where the thermostat is set.
Exposed ducts can be repaired by sealing the connections with duct sealant (also called duct mastic). In addition, insulating ducts that run through spaces that get hot in the summer or cold in the winter (like attics and crawlspaces) can save significant energy.
Insulation helps keep your home cool in the summer and warm in the winter. There are several common types of insulation, such as fiberglass (in batt, blanket and blown forms), cellulose, rigid foam board and spray foam. Insulation performance is measured by R-value - its ability to resist heat flow. Higher R-values mean more insulating power.
SRP recommends minimum insulation levels of R-19 for exterior walls (total wall system) and R-30 for ceilings.