A statistical measurement of the heating season effectiveness of ceiling insulation in San Diego

Retrofit R-19 ceiling insulation is evaluated as a natural gas conservation measure in San Diego, California. A statistical measurment comparing 82 test homes and 104 matched control homes resulted in a 95% confidence interval lower bound saving of 21% of total December–February natural gas consumption, an energy payback period of less than one year, and a life cycle cost payback of 6.4 years (assuming a 10% annual fuel escalation factor and a 6% discount rate). An ASHRAE heating degree day analysis was performed giving similar results. It is also demonstrated that insulation saves substantial amounts of natural gas even in the mild fall season and that no statistically significant increase in electricity consumption resulted from installation of insulation. Finally, no evidence was found to support the theory that, due to the mild climate in San Diego, significant numbers of conservation minded people are turning off their furnaces in winter. Addition of insulation enabled test homes to maintain “comfortable” temperatures with smaller expenditures of natural gas.