DOE's Proposed Climate Zones FAQs

The following frequently asked questions (FAQs) are provided help answer your questions about the DOE's proposed climate zones. An explanation of the development of new climate zones (PDF, 1.5 MB) is also available for review. Download Acrobat Reader

Why are new climate zones being proposed?
How will changing the climate zones affect code requirements?
What is wrong with the current climate zones?
Why are there still so many climate zones?
Why are there so few climate zones in this proposed change?
How are the proposed climate zones linked to other code change proposals?
How do the old climate zones relate to the proposed climate zones?
How did you develop the new climate zones?
Why is precipitation used in the climate zone definitions?

Q: Why are new climate zones being proposed?

The new climate zones are intended to make the IECC shorter and easier to use. In addition to enabling the elimination of more than 40 pages of maps and many pages of commercial envelope tables, they will allow commercial and residential sections of the code to use a common set of climate zones. For the first time, users of the IECC will be able to determine what requirements apply anywhere in the United States without having to obtain climate data (e.g. heating degree days) from some other source.

Q: How will changing the climate zones affect code requirements?

The climate zones have been developed with the intent of having a neutral impact on code stringency-that is, neither increasing nor decreasing the overall stringency relative to existing requirements. However, it is not possible to change something as fundamental to many of the IECC requirements as climate without affecting some of the requirements one way or another. We hope interested and affected parties will conclude that the benefits of a shortened and streamlined code outweigh the inconvenience and dislocation resulting from minor changes in requirements in some locations--which were unavoidable.

Q: What is wrong with the current climate zones?

The existing climate zones suffer from several shortcomings that the new zones attempt to remedy:

Too many zones within individual jurisdictions. Many code users have complained to DOE that the code's requirements change too much within code jurisdictions. Reducing the number of zones by roughly half will mean that far fewer users will need to keep track of requirements that differ across the region in which they practice.
Poor representation of cooling issues. The existing zones are based entirely on heating degree-days, which means they do a rather poor job of distinguishing climate factors that affect cooling loads. The new zones better reflect factors that impact cooling, such as cooling degree days, high wet bulb temperatures, and variations in solar radiation.
Inconsistent use in the code. The existing climate zones are not used consistently in the IECC. For example, the IECC's residential requirements are mostly based on heating degree-days, while its commercial requirements vary by several factors. Also, current residential requirements sometimes reference the climate zones, sometimes pure heating degree-days, and sometimes the county-by-county zone assignments. The proposed new climate zones are designed to consolidate the various code criteria around a common base.
Outdated zone definitions. The current climate zones have a, b, and c subdivisions that were defined around an older set of commercial requirements that have been supplanted by more up-to-date ASHRAE materials.

The fundamental intent of the new zones is a code that is shorter, more consistent, and easier for everyone to use.

Q: Why are there still so many climate zones?

There is no single correct answer to the question of how many climate zones are really needed for building energy codes. A large number of zones enable climate-related requirements to be accurately tailored to each climate. A small number of zones keeps the code smaller and easier to use and requirements more uniform. The 15 proposed zones reduce the number of zones by roughly half yet enables code requirements to be presented with reasonable accuracy.

The proposed climates zones are integrated with code changes for commercial buildings (in Chapter 8 of the IECC) and for residential buildings (in Chapters 4, 5, and 6) of the IECC and in the IRC.

The selected thermal criteria resulted in mostly horizontal bands across the country with the hottest zone (#1) occupying the southern tip of Florida and Hawaii to the coldest zone (#8) covering the Northern half of Alaska.

Q: Why are there so few climate zones in this proposed change?

The feedback received from DOE's Building Energy Codes Program over nearly a ten year period of assisting state and local jurisdictions in implementing building energy codes has consistently indicated that users feel there have been too many climate zones. In quite a few cases, state representatives have asked that DOE create implementation materials based on a smaller number of climate zones. Another indication that there are currently too many climate zones is the high degree of similarity between individual envelope requirement tables in Chapter 8. Additional climate zones are only necessary when they correspond with significant differences in the code requirements they help implement.

Q: How are the proposed climate zones linked to other code change proposals?

The proposed climates zones are being coordinated with code change proposals for commercial buildings (in Chapter 8 of the IECC) and for residential buildings (in Chapters 4, 5, and 6) of the IECC and in the IRC.

The coordinated changes in the other chapters mostly just involve updating the climate zone references to the new climate zones.

Q: How do the old climate zones relate to the proposed climate zones?

The following table outlines how the old climate zones map to the proposed climate zones. The mappings shown below are approximate, see the climate zone development white paper (PDF, 1.5 MB) for the exact definitions of the new zones.

Proposed New Climate Zone	Old Climate Zones
1	1
2	1b,2,3,4
3	4a,5,6,7
4	8,9,10,11
5	12,13,14
6	15,16
7	17
8	18,19

Q: How did you develop the new climate zones?

DOE's IECC proposal for new climate zones is the culmination of a nearly two-year process involving numerous discussions, several meetings at national conferences, a white paper, and several months of technical work at Pacific NW National Laboratory (PNNL). There was broad agreement early in the process among representatives of the codes development community that the IECC climate zones could be improved and that there were too many climate zones, but there was far less agreement on how to fix them.

Initial technical work at PNNL focused on statistical methods for defining zones. However, direct use of the statistical results was ultimately rejected because the statistically-developed climate zones tended to be difficult to explain and to lack the simplicity and geographic coherence that would make them administratively efficient to use.

Instead, climate zones were developed based on a traditional system of climate classification used in many other disciplines. That classification provided quantitative definitions for three major climate types--humid climates, dry climates, and marine climates. These major climate types are important for buildings because they affect solar loads, humidity, daily temperature ranges, and whether heating and cooling seasons are short and intense or long and mild. These are all aspects of climate that cannot be addressed simply by looking at heating degree days--the primary basis for the current zones.

In addition to the major humid/dry/marine climate types, climate divisions were defined based on thermal criteria. But instead of using heating degree days for the entire country, as has been done for the Model Energy Code (MEC) and IECC in the past, thermal divisions for cooling-dominated regions of the country were defined based on cooling degree days. The selected thermal criteria resulted in mostly horizontal bands across the country with the hottest zone (#1) occupying the southern tip of Florida to the coldest zone (#8) covering the Northern half of Alaska. Regular increments of heating and cooling degree days were selected that (1) worked well climatologically, (2) facilitated the representation of current code requirements, and (3) enabled a substantial reduction in the number of zones.

The resulting climate zones can be thought of as the intersection of the three major climate types with 8 thermal bands that progress northward from very hot to very cold. However, because the Marine zones are by definition neither very hot nor very cold, separate Marine zones were defined only for the intermediate thermal zones #3, #4, and #5. In addition, above Zone 6 the humid/dry distinction was dropped, because humidity is important only where there is a need for cooling.

An explanation of the development of new climate zones (PDF, 1.5 MB) is also available for review. Download Acrobat Reader

Q: Why is precipitation used in the climate zone definitions?

Precipitation is used in the definitions of the major climate types--humid/dry/marine, because that definition is part of a system of world climate classification developed by an early Twentieth Century climatologist named Wladimir Koppen. Koppen's classification is quantitative, universally applicable, and widely-accepted. But most important for the new climate zones, the climate divisions he defined are located where PNNL's statistical analyses determined they needed to be for effective climate zones for buildings.

While precipitation does not relate directly to building energy use, it does correlate well on an annual basis with a number of climate parameters that are important to building energy use and energy code requirements. These include the intensity of solar radiation, average cloud cover, average relative humidity, diurnal temperature range, and wet and dry bulb design temperatures.