A heating degree day (HDD) or cooling degree day (CDD) is an index used to determine the amount of energy needed to heat or cool a building. The number of heating or cooling degrees in a day is defined as the difference between a base temperature – 65° Fahrenheit – and the outside temperature. If, for example, the temperature outside is 55° F, then we would say it is a ten-degree day. Organizations, such as the State of Iowa, use this information to estimate seasonal heating and cooling demands.
Important Update
Details
Effective May 4, 2026, the email domain for Iowa Department of Administrative Services employee addresses and inboxes has changed from @iowa.gov to @das.iowa.gov.