Glossary · Energy, bills & ratings

Cooling degree days (CDD)

Also called: CDD18 · CDD65

A measure of how hot a place is: each day adds how far its average temperature rises above 65°F. More degree days means more air conditioning.

What it means

A day averaging 78°F adds 13 cooling degree days. Yearly totals track air-conditioning demand. Where cooling degree days outnumber heating degree days, as in Phoenix, Houston or Miami, the climate is cooling-dominated and summer bills matter most.

Why it matters in an audit

CDD help an auditor judge how much cooling efficiency (SEER2, EER2), window SHGC and attic radiant barriers matter in your climate.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Worked example (EIA)	High 90°F, low 66°F: mean 78°F, so 13 CDD	eia.gov ↗

Sources

Learn more here

Related terms

Heating degree days (HDD) A measure of how cold a place is: each day adds how far its average temperature falls below 65°F. More degree days means more heating.
Heating-dominated vs cooling-dominated climate Whether a place needs more energy for heating or for cooling over a year, which changes which upgrades and equipment matter most.
SEER / SEER2 An air conditioner's or heat pump's cooling efficiency averaged over a whole cooling season; higher is better.
Solar heat gain coefficient (SHGC) The share of the sun's heat a window lets into the house, from 0 to 1; lower keeps homes cooler, higher adds free winter heat.
Full-load hours (equivalent full-load hours) The number of hours a heating or cooling system would have to run flat out to deliver a whole season's heating or cooling.
Climate normals Thirty-year averages of temperature, degree-days, precipitation and other weather at a station, used as the typical climate for a place.

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