I am using the guidelines established by the CDA. As indicated in the FPN, the CDA guidelines utilize the average of the 2% ASHRAE design temperatures for each region and major city in the state.
The guildelines and sliding scale card can be obtained FREE from www.copper.org
Bryan P. Holland, ICC Electrical Code Official
CBO, Plans Examiner, Inspector, Instructor
Secretary - IAEI Florida Gulf Coast Division
Secretary - BOAF Gulf Coast Chapter