Outdoor context Climate & comfort Regional

Climate zone effects

The same reading means different things in cold-dry, hot-humid, and temperate climates. The interpretation adjusts.

Updated 2026-05-25 1 min read

Also in: Français Español

A United States map shaded by Köppen–Geiger climate types, illustrating the climate diversity the article cross-references to ASHRAE/IECC zones.
Photo: Puwadon Sang-ngern via Pexels

Indoor air quality is not climate-neutral.

Köppen climate types of the United States, shaded by zone with a full legend.
Köppen–Geiger climate types of the United States - a climate-science view of the same diversity the building-code IECC / ASHRAE 169 zones describe. Map by Adam Peterson via Wikimedia Commons (CC BY-SA 4.0); climate data from PRISM Climate Group, Oregon State University.

The ASHRAE 169 climate zones and the parallel IECC energy-code zones divide North America into 8 zones (1 hot-humid to 8 subarctic), each with characteristic indoor-air pressure points the interpretation layer adjusts for.

Cold and very cold zones (ASHRAE 5–8 / Köppen Dfa, Dfb, Dfc - New England, Upper Midwest, Prairies, Yukon): homes are tightly sealed for energy efficiency, indoor humidity drops dangerously low in winter (often under 25%), CO2 accumulates faster in sealed bedrooms, and HRV/ERV units are nearly mandatory. The dashboard flags low-humidity health risks more aggressively in these zones and recommends balanced ventilation more often.

Hot-humid zones (ASHRAE 1–3 / Köppen Cfa, Csa - Gulf Coast, Southeast, southern California coast): mold risk dominates. Air conditioning is the primary humidity-control mechanism; when it is undersized or running in "fan only" mode, RH climbs above 60% on coastal nights and stays there. Dust mites and mold thrive year-round. The dashboard's mold-risk threshold is more sensitive in these zones.

Hot-dry (ASHRAE 2B/3B / Köppen BWh, BSk - Southwest US): low ambient humidity makes infiltration of outdoor pollutants (dust, ozone, wildfire smoke during summer) more impactful because there is no humidity buffer for irritation. Temperate marine (ASHRAE 4C / Köppen Csb, Cfb - Pacific Northwest, BC coast): mild outdoor air most of the year but wildfire smoke season has expanded dramatically; mold pressure is moderate. The same indoor PM2.5 reading carries a different action-level depending on which zone you are in; the dashboard reads your geocoded climate zone from setup and weights accordingly.

References

  1. ASHRAE Standard 169 - Climatic data for building design www.ashrae.org
  2. IECC - Climate zones for energy code codes.iccsafe.org
  3. WHO - Guidelines for indoor air quality: dampness and mould www.who.int
  4. EPA - Particulate matter basics www.epa.gov

Understand the reading

Find the source

Take action