The Home Almanac
The five regions, and the sources behind the calendar
The almanac's regional notes use the U.S. Department of Energy's Building America climate regions, as drawn in the 2021 update by Pacific Northwest National Laboratory. We fold DOE's eight regions into five almanac regions because the maintenance calendar changes with heating season, cooling season and rainfall, not with every zone boundary.
North: Cold and Very Cold
Building America Cold and Very Cold (IECC zones 5, 6 and 7), plus Alaska's Subarctic (zone 8)
Where: Roughly the northern half of the country: New England, the Great Lakes, the upper Midwest and northern Plains, the Rockies and high country, and the Front Range. DOE's map marks the far tips of North Dakota and Maine and southern Alaska as Very Cold; Chicago, Minneapolis and Denver all sit in the Cold region.
What drives the calendar: A real heating season of 5,400 to 12,600 heating degree days. Frozen pipes, ice dams, furnace reliability and snow load are the headline risks. Cooling is a short season.
Mid-country: Mixed-Humid
Building America Mixed-Humid (the moist parts of IECC zones 3 and 4)
Where: From the Maryland coast through North Carolina, across the mid-South and Ohio Valley, and west to cover most of Kansas and Oklahoma. Atlanta's Fulton County is Mixed-Humid.
What drives the calendar: More than 20 inches of rain a year, a moderate winter with some months averaging below 45 F, and a humid summer. Both the furnace and the air conditioner earn their keep, and moisture control matters year-round.
Southeast and Gulf: Hot-Humid
Building America Hot-Humid (the moist parts of IECC zones 1, 2 and 3)
Where: Eastern Texas through the Gulf Coast and Florida, reaching up to mid-Georgia, plus Hawaii and Puerto Rico. Miami-Dade and New Orleans are Hot-Humid.
What drives the calendar: Long, humid summers (3,000 or more hours at a 67 F wet-bulb temperature) and mild winters. Air conditioning, condensate drains, mold and hurricane season drive the calendar; hard freezes are rare but do happen.
Southwest: Hot-Dry and Mixed-Dry
Building America Hot-Dry (dry parts of IECC zones 2 and 3) and Mixed-Dry (IECC zone 4B)
Where: Eastern and southern California along the border through Arizona, New Mexico and the western half of Texas. Phoenix and Los Angeles County are both classed Hot-Dry.
What drives the calendar: Less than 20 inches of rain a year. Hot-Dry areas stay above a 45 F monthly average all year; Mixed-Dry areas (the high desert) get real winters. Cooling load, dust, wildfire exposure and dry indoor air set the pace. Desert nights can still freeze exposed pipes.
Pacific coast: Marine
Building America Marine (the C moisture category of IECC zones 3 and 4)
Where: The far western Pacific coast from the Canadian border to mid-California: Seattle, Portland's coast, Humboldt and San Francisco. Inland valleys and Southern California fall in other regions.
What drives the calendar: Mild winters (coldest month between 27 F and 65 F), cool summers (warmest month under 72 F) and a dry summer with a long wet season. Rain management, moss, gutters and damp crawl spaces matter more than extremes of heat or cold.
How DOE draws the lines
DOE classifies every US county. A Hot-Humid county gets more than 20 inches of rain a year and spends 3,000 or more hours at a 67 F wet-bulb temperature or higher. Mixed-Humid counties get the same rain with about 5,400 heating degree days or fewer and winter months averaging below 45 F. Hot-Dry and Mixed-Dry counties get less than 20 inches of rain; the Hot-Dry ones stay above a 45 F monthly average all year. Cold counties run 5,400 to 9,000 heating degree days and Very Cold ones 9,000 to 12,600; the Subarctic region (12,600 and up) exists only in Alaska. Marine counties have a coldest month between 27 and 65 F, a warmest month under 72 F, and a dry summer.
The 2021 update reassigned about 10 percent of counties, most of them to a warmer zone, so older maps may put you in the wrong region. If you are near a boundary, read both regions' notes; the tasks are the same, only the timing moves.
Where the tasks come from
Every task on the almanac traces to a source we read, listed at the bottom of its month page. The recurring ones: ENERGY STAR's heating and cooling maintenance checklist, DOE's Energy Saver guides, the U.S. Fire Administration's home fire safety pages, the Consumer Product Safety Commission's seasonal safety releases, the EPA's guides on mold, radon and air filters, the American Red Cross on frozen pipes, NOAA on hurricane season, CAL FIRE and NFPA on defensible space, and the University of Georgia, University of Minnesota, University of Florida and North Dakota State extension services. Where two sources give different intervals (water heater flushing is the usual example), the page says so and tells you to follow your equipment's manual.
References
- Guide to Determining Climate Zones by County: Building America and IECC 2021 Updates (PNNL-33270). Pacific Northwest National Laboratory for the U.S. Department of Energy. https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-33270.pdf
- Guides and Case Studies for Cold and Very Cold Climates. U.S. Department of Energy. https://www.energy.gov/cmei/buildings/guides-and-case-studies-cold-and-very-cold-climates
- Guides and Case Studies for Mixed-Humid Climates. U.S. Department of Energy. https://www.energy.gov/cmei/buildings/guides-and-case-studies-mixed-humid-climates
- Guides and Case Studies for Hot-Humid Climates. U.S. Department of Energy. https://www.energy.gov/node/772726
- Guides and Case Studies for Hot-Dry and Mixed-Dry Climates. U.S. Department of Energy. https://www.energy.gov/cmei/buildings/guides-and-case-studies-hot-dry-and-mixed-dry-climates
- Guides and Case Studies for Marine Climates. U.S. Department of Energy. https://www.energy.gov/cmei/buildings/guides-and-case-studies-marine-climates
Every fact and number on this page comes from one of the sources above, read during the writing of this page. Codes and standards vary by jurisdiction and edition; your local code and your equipment's manual control.