Climate Zones and Degree Days

IECC Climate Zone Map

I recently learned about the Climate Zone Map put together by the folks at the International Energy Conservation Code (IECC).  The climate zones help energy professionals decide which building materials work best in which regions to help optimize energy efficiency.  You can use this link to see which climate zone your county in your state falls under and which building requirements (mainly dealing with the building envelope) work best in that zone.   Instead of lumping in each area of a state and generalizing the climate characteristics, climate zones define a climate for each county in a state!  For instance, the state of California has 5 climate zones within it!

The climate zone number (1-8) relies on temperature variations using Heating Degree Days (HDD) and Cooling Degree Days (CDD).   The zones are then further divided into moisture zones: Marine, Dry, Moist.

In doing research on climate zones, my biggest question was what actually defines one! This information was very hard to find, but luckily the customer support at the residential energy code program ( was able to help me out.  Here is a link to the PDF describing the IECC Climate Zone Definitions and the table below defines the zones:

The PDF uses 2 acronyms to define a climate zone: CDD and HDD.  These stand for Cooling Degree Days (CDD) and Heating Degree Days (HDD).  To learn more about what a degree day is an how to calculate it, check out this great article on "What is a Degree Day".  The same site that describes a degree day allows you to calculate Degree Days for your location.  Using the result of this calculation, you can then use the IECC climate zone definition PDF (or the Table above) to figure out what climate zone you are in; that is if you don't like using the much simpler method of looking at a map!  Just remember that if you are using Fahrenheit, use the IP Unit side of the table; if using Celsius use SI Units.

At this point you are probably asking yourself, "Why do I care about this?".  Here's why.  Let's say you are reading an article describing some great new energy saving device (that somehow relates to saving heating and cooling costs; costs that are dependent on the climate).  The person writing the article installed this energy saving device in an area of the country that is not where you live.  To estimate how that device would work in your area of the country, you would refer to the map of the Climate Zones to see how your area compares to their area (don't forget to look at the sub-climate)!  If you are in Zone 1 (Miami), and they are in Zone 8 (part of Alaska), chances are you are going to have a much different experience with a product based on your very different climates!  However, if you are in the same or similar zones, your experiences should be similar.

The climate zones are a great tool for energy professionals and a great point of reference for the rest of us!

enjoyed our post? let others know: 


Thanks for the that. Would be nice if you had a map for AK. But the box on the current image still answered my questions.
Nice explanation, Chris. I love the website! Not only can you get good data for your location, but they also have detailed explanations of how degree days are calculated and what they mean.

Post new comment

Subscribe to Comments for "Climate Zones and Degree Days"