Why Texas needs six answers rather than one
The reason a single national answer fails in Texas is that the state spans four building climate zones. The Gulf Coast and the Rio Grande Valley are zone 2A — hot and humid, cooling-dominated, with outdoor dew points in the seventies for months. North and East Texas are zone 3A: humid, but with a genuine winter that brings condensation on cold glass as well as summer moisture. West Texas and the Panhandle are 3B and 4B, hot-dry and cold-dry, where indoor air in a heated house can drop below 20% and split furniture.
That matters because the two halves of the state need opposite equipment. A Houston house needs dehumidification and sealed, conditioned crawl spaces; an Amarillo house needs humidification and air sealing against dry infiltration. Advice written for one is actively harmful in the other, which is why these guides are organized by city rather than by product.
Two things are true almost everywhere in the state, though. Nearly all Texas housing is cooling-dominated, so air conditioning is the largest dehumidifier most homes own — and an oversized system that satisfies the thermostat in eight minutes never runs long enough to remove water, which is the single most common cause of a house that is cold and clammy at once. And Texas summers have been getting more humid: the Austin–San Antonio corridor has seen its average dew point rise by roughly three degrees over the historical record, which is a meaningful shift in how much water an air conditioner has to remove.
The four climates inside the state line
Zone 2A — the Gulf Coast and the Valley
Houston, Corpus Christi, Beaumont, the Rio Grande Valley. Outdoor dew points in the low seventies from May to September, over 100 days a year above 90 °F, and rainfall up to 50 inches. Ventilating with outdoor air makes a house wetter for half the year.
Zone 2A/3A — Central Texas and the Hill Country
Austin, San Antonio, New Braunfels, Waco. Humid subtropical shading into semi-arid to the west. Annual humidity around 67%, but with far larger daily swings than the coast — humid mornings and dry afternoons in the same day.
Zone 3A — North and East Texas
Dallas–Fort Worth, Tyler, Longview, Texarkana. Humid summers plus a real winter, which is the combination that produces both summer mold and winter window condensation in the same house six months apart.
Zone 3B/4B — West Texas and the Panhandle
El Paso, Lubbock, Amarillo, Midland. The opposite problem: annual rainfall under 20 inches, indoor humidity in the teens during a heated winter, evaporative cooling in summer, and damage to timber, floors and instruments rather than mold.
City guides
10 written so far, out of 136 Texas cities and towns listed below. Cities without a link are on the list and not yet written.
Houston
Houston is one of the most demanding humidity climates in the United States. The outdoor air carries more water than the inside of a well-run house for roughly five months of the year, which means the ordinary advice to open a window is wrong here for most of the cooling season.
San Antonio
San Antonio sits on the line between humid subtropical and semi-arid, which gives it something the Gulf Coast does not have: a daily swing large enough that the right hour of the day is a genuine humidity tool.
Dallas
Dallas is where the two halves of this site meet. Summers are humid enough to grow mold on a cooled exterior wall; winters are cold enough to put water on the glass and dry the air out enough to gap a floor. A house here needs a strategy for each.
Austin
Austin has one of the longest cooling seasons of any major American city — 123 days a year at or above 90 °F, of which 29 reach 100 °F. That length, rather than any single humid day, is what shapes a house here.
Fort Worth
Fort Worth sits thirty miles west of Dallas and that is enough to matter. Rainfall drops by about five inches a year, the air is a shade drier, and the balance of problems shifts a little further toward the winter half of the year.
Corpus Christi
Corpus Christi is one of the most humid cities in the United States, and more humid than Houston. At 76.1% annually, with a mean dew point of 63.4 °F, this is air that a building has to be actively defended against for most of the year.
El Paso
El Paso is at the same latitude as Dallas and in the same state as Houston, and it has the opposite problem from both. This is a desert: 8.8 inches of rain a year, 302 sunny days, and an annual mean dew point of 35.4 °F.
Lubbock
Lubbock sits at 3,202 feet on the High Plains, with a cool semi-arid climate, 18 inches of rain a year and some of the strongest sustained wind of any American city. The result is a house that is too dry in winter and too dry in summer, for two different reasons.
McAllen
McAllen is the contradiction in Texas climate data: classified as hot semi-arid on rainfall, and yet running high enough dew points that the heat index is routinely brutal. Its cooling season is one of the longest in the country.
Tyler
East Texas gets almost as much rain as the Gulf Coast, and unlike the coast it also gets a genuine winter. Add the tree cover of the Piney Woods, which keeps roofs and north walls damp long after rain, and Tyler becomes one of the harder climates in the state for a building.
The Gulf Coast
The most humid part of the state and the most demanding on a house. Outdoor dew points sit in the low seventies from May into September, so the air itself carries more water than the inside of a well-run house.
IECC 2A — hot-humid. Here, ventilation is not a humidity tool for half the year. Air conditioning and dehumidification do the work, and the failure modes are oversized systems, vented crawl spaces and ducts running through hot humid attics.
- Houston
- Pasadena
- Pearland
- League City
- Sugar Land
- Baytown
- Missouri City
- Conroe
- Beaumont
- Port Arthur
- Texas City
- Galveston
- Friendswood
- Deer Park
- La Porte
- Alvin
- Angleton
- Lake Jackson
- Rosenberg
- Katy
- Tomball
- Humble
- Orange
- Victoria
- Bay City
- El Campo
- Wharton
South Texas and the Rio Grande Valley
Coastal cities here are as humid as Houston with even longer cooling seasons. Inland and westward toward Laredo and Del Rio the air dries out quickly, and the problem changes with it.
IECC 2A — hot-humid, drying westward. The Valley runs a cooling season of eight months or more. Houses are almost universally slab-on-grade, so the classic crawl-space problem is absent and duct condensation in hot attics takes its place.
- Corpus Christi
- Laredo
- McAllen
- Brownsville
- Edinburg
- Mission
- Pharr
- Harlingen
- Weslaco
- San Benito
- Kingsville
- Alice
- Beeville
- Portland
- Rockport
- Port Lavaca
- Del Rio
- Eagle Pass
- Uvalde
Central Texas and the Hill Country
Humid subtropical on its eastern edge and close to semi-arid on its western one. Annual humidity around 67%, but with much larger daily swings than the coast — saturated at dawn, comfortable by mid-afternoon.
IECC 2A shading into 3A. The daily swing is what makes this region different. A house here can be ventilated usefully in the late afternoon in a way that a Houston house cannot, and timing matters more than equipment.
- San Antonio
- Austin
- Round Rock
- New Braunfels
- San Marcos
- Georgetown
- Cedar Park
- Pflugerville
- Leander
- Killeen
- Temple
- Waco
- Bryan
- College Station
- Kyle
- Buda
- Seguin
- Boerne
- Kerrville
- Fredericksburg
- Marble Falls
- Bastrop
- Lockhart
- Copperas Cove
- Belton
- Brenham
North Texas
Humid summers and a genuine winter. This is the part of Texas where a single house can grow mold in August and run with condensation on the glass in January, which needs two different strategies six months apart.
IECC 3A — mixed-humid. North Texas is the region where the winter half of this site matters. Freezes are routine, single-pane and older windows are common in the pre-war stock, and heating dries the air enough to notice.
- Dallas
- Fort Worth
- Arlington
- Plano
- Garland
- Irving
- Grand Prairie
- Frisco
- McKinney
- Mesquite
- Carrollton
- Denton
- Richardson
- Lewisville
- Allen
- Flower Mound
- North Richland Hills
- Mansfield
- Rowlett
- Euless
- Bedford
- Grapevine
- Keller
- Coppell
- Burleson
- Cleburne
- Weatherford
- Wichita Falls
- Sherman
- Denison
- Corsicana
East Texas
The Piney Woods are the wettest part of the state away from the coast, with heavy rainfall, dense tree cover and shaded houses that dry slowly after rain.
IECC 3A — the most humid inland region. Shade is the local complication. Tree cover keeps roofs, north walls and crawl spaces cool and damp for far longer after rain than the same construction would stay damp in open country.
- Tyler
- Longview
- Texarkana
- Lufkin
- Nacogdoches
- Marshall
- Palestine
- Athens
- Jacksonville
- Paris
- Huntsville
- Livingston
- Kilgore
- Carthage
- Center
West Texas and the Panhandle
The opposite half of the state. Rainfall under 20 inches a year, low dew points, and heated winters that take indoor humidity into the twenties or below.
IECC 3B and 4B — hot-dry and cold-dry. Here the equipment list inverts: humidifiers rather than dehumidifiers, air sealing rather than ventilation, and evaporative cooling in summer, which deliberately adds moisture and needs its own controls.
Common questions
What is a good indoor humidity for a house in Texas?
Between 40 and 50% almost everywhere in the state, with two adjustments. On the Gulf Coast and in the Valley, treat 55% as a ceiling you should not sit above in summer, because outdoor dew points in the seventies make anything higher a mold risk on cooled surfaces. In West Texas and the Panhandle, treat 35% as a floor you should not fall below in winter, because the outdoor air is genuinely arid and a heated house will drift into the twenties on its own.
Why is my Texas house humid even with the air conditioning running?
Almost always because the system is oversized for the house. An air conditioner removes water only while it runs, and a unit with too much capacity cools the air to the set temperature in a few minutes and shuts off, leaving the moisture behind. The symptoms are a house that feels clammy at 74 °F, short cycles you can hear, and humidity readings in the sixties. A variable-speed system, a longer runtime setting, or a standalone dehumidifier all fix it; a colder thermostat setting does not.
Does the whole state have the same humidity problem?
No, and this is the thing most national advice gets wrong about Texas. El Paso and Houston are in the same state and at a similar latitude, and they have opposite problems: Houston averages close to 75% relative humidity with 50 inches of rain, El Paso is a desert with under 10. A dehumidifier is essential equipment in one and a waste of money in the other.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions
- NOAA / NWS 1991–2020 Climate Normals, via the city climate tables on Wikipedia
- US Department of Energy — Building America climate zone definitions
- EPA — Indoor Air Quality: moisture control and mold
- DOE 10 CFR 430 — dehumidifier test procedure (2019 method)