Secondary Author(s)

Sonne, Jeffrey; Vieira, Robin; Klongerbo, Jon

Report Number






Installed central air conditioning system capacities in 368 recently-built Florida homes were compared with Manual J load values calculated from house audit data. Over 50% of the homes had installed systems with a cooling capacity greater than 120% of the calculated Manual J value. Thirty-one percent of the 78 heat pump homes in this study had installed heating capacity greater than 120% of the calculated Manual J value. Using submetered data from the air conditioning system, a definite increase in peak energy use was observed for systems sized over 120% of Manual J calculations. The effect of system sizing on the system run-time fractions of units is shown. The homes that had units sized smaller than the calculated Manual J value tended to have higher percentages of maximum hourly run-time fractions. There was little difference in binned percentages of large runtime fractions between homes with installed-to-calculated ratios of 1.0 to 1.2 and those with installed-to-calculated ratios greater than 1.2.

Date Published



Reference Publication: James, P., J.E. Cummings, J. Sonne, R. Vieira, J. Klongerbo, “The Effect of Residential Equipment Capacity on Energy Use, Demand, and Run­Time,” ASHRAE Transactions 1997, Vol 103, Pt. 2., American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., Atlanta, GA.

Local Subjects



FSEC Energy Research Center® Collection



Rights Statement

In Copyright