Assuming that the energy used in Iowa City comes from Coal a normal air-forced heating and cooling home uses 5.25 tons of CO2 on electricity and Gas. A LEED home only uses 3.88 Tons of CO2. These numbers are calculated by assuming that each kWh of electricity creates 2.25 pounds and each kWh of gas creates 1.95 pounds of CO2.
The LEED home saves 1.37 tons of CO2 per year