Austin runs an annual average of 67.1% relative humidity with a dew point of 54.6 °F. Hold 40–50% indoors and the rest of this page is how.
- Annual relative humidity
- 67.1%
- Annual dew point
- 54.6 °F
- Days at or above 90 °F
- 123
- Annual rainfall
- 34.32 in
- Indoor target
- 40–50%
The climate, in numbers that matter to a building
Austin is humid subtropical (Köppen Cfa) sitting on the Balcones Escarpment, which puts the western half of the metro noticeably drier than the eastern half. The annual relative humidity averages 67.1% and the annual dew point 54.6 °F, but those averages hide a very large daily range: humid mornings from Gulf inflow give way to afternoons that are genuinely dry.
The defining figure is the heat rather than the moisture. Highs reach 90 °F on 123 days a year and 100 °F on 29 of them, with a July average high of 96.6 °F. That is a cooling season running from April into October, and it means air conditioning here is not an occasional appliance but the dominant environmental system in the house for half the year.
One local trend is worth stating plainly because it changes the design assumption: the Austin–San Antonio corridor has seen its average dew point rise by roughly three degrees over the historical record, from about 64.5 to 67.5 in the warm season. A three-degree dew point rise is a meaningful increase in the amount of water a cooling system has to remove, and it is part of why houses that used to be comfortable at a given thermostat setting no longer are.
Through the year in Austin
| Season | What the outdoor air does | What that does to a house here |
|---|---|---|
| Spring | Wet and increasingly humid; May and June are the most humid months | Cooling starts and the moisture load arrives before the extreme heat does |
| Summer | Very hot, often with dry afternoons and humid mornings; long rainless spells | Heat-dominated load; watch for systems that cool fast and leave humidity behind |
| Fall | A second rainfall peak, then rapid drying | The best ventilation window; also when summer growth becomes visible |
| Winter | Mild with occasional hard freezes | A few weeks of dry indoor air and brief window condensation during cold snaps |
What this climate does to a house here
The problems below are the ones that turn up repeatedly in Austin specifically, rather than the general list.
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A long cooling season that never lets the house dry out
Five months of continuous cooling means five months of surfaces held below the outdoor dew point. Nothing dramatic happens on any given day, which is exactly the problem: closets, storage rooms and the backs of furniture accumulate a small surplus for months, and the growth appears in September.
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Oversized systems in new construction
Austin has built a great deal of new housing quickly, and oversizing the cooling equipment is a common shortcut. The result is short cycles, poor moisture removal, and a house that reads 74 °F and 62% at the same time. It is the most common local complaint that has nothing to do with the weather.
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Ducts in unconditioned attics
A vented Austin attic in August is extremely hot and, during humid pushes, wet. Cold ducts running through it condense wherever the insulation is gapped or crushed, and the water shows up on the ceiling below in a straight line.
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Hill Country houses on rock and slab
West of the escarpment, houses frequently sit on thin soil over limestone with slab foundations. Ground moisture is less of an issue than east of the city, but surface water runs fast in heavy rain and the humidity problems concentrate around the drainage rather than the soil.
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Winter dryness in a city that does not plan for it
Hard freezes are infrequent enough that few Austin houses have any humidification, so when one arrives the indoor humidity falls into the twenties within a day. It rarely lasts long enough to damage anything, but it is uncomfortable and it does move timber floors.
What is your reading telling you?
- Dew point
- 53 °F
- Mold risk, cold walls
- Moderate
Still inside the accepted range, but this is where cold surfaces begin to sweat.
Every fix that works here, cheapest first
The complete ladder for an Austin house. The length of the cooling season means the priority is a strategy that holds for months rather than a fix applied once.
Ventilate in the late afternoon, and not at all on humid mornings
The daily swing gives Austin a real ventilation window most days between mid-afternoon and early evening. On mornings when Gulf air has pushed in, keep the house closed — the outdoor dew point is above the indoor one and opening up adds water.
Remove the sources you control
Bathroom fan running during and after showers with the door shut, lids on pans, dryer vented outside, no laundry drying indoors. Over a five-month cooling season these add up to a great deal of water the system does not have to remove.
Give enclosed rooms an air path
Closets and rooms with a supply register and no return run both colder and more humid than the rest of the house. A door left ajar, an undercut or a transfer grille is free and fixes the majority of local closet mold complaints.
Fan to auto, thermostat up a degree
Auto stops the fan re-evaporating condensate off the coil between cycles. A slightly higher set point produces longer runtimes, and longer runtimes are what remove water. Both are free and both usually lower the reading.
Check where every duct ends
Bathroom and kitchen extraction that terminates in the attic rather than outside is common and puts every shower into the hottest, most humid part of the building. Following each duct physically takes an hour and occasionally solves the whole problem.
A dehumidifier for the cooling season
A 30 to 50 pint unit under the 2019 rating, set to 50%, run through the summer. In a large house with a system that will not hold humidity, a ducted whole-house dehumidifier is the durable answer and lets you raise the thermostat rather than lower it.
An ERV for fresh air in a tight house
New Austin construction is airtight enough to need mechanical ventilation. An energy recovery ventilator brings fresh air in while transferring much of the moisture back out, which is the correct choice in a cooling-dominated humid zone. An HRV is not.
Right-size the cooling equipment when it is replaced
A variable-speed or two-stage system sized to a real load calculation rather than a rule of thumb runs longer at lower capacity, and long runtimes are how a house gets dry. This is the single highest-value decision available at replacement time.
Seal and insulate the ducts, or bring the attic inside
Sealing duct joints and restoring insulation stops the condensation and recovers cooling capacity at the same time. Converting to an unvented conditioned attic is expensive and, in this climate, one of the most effective envelope changes available — it removes the hot humid space the ducts run through altogether.
Local construction, and why it changes the answer
Austin housing splits along the Balcones Escarpment. East of it, deeper soils and higher humidity give the standard Central Texas pattern. West of it, houses sit on thin soil over limestone, which drains fast, so the humidity problems concentrate in the building rather than in the ground — ducts, attics and enclosed rooms rather than crawl spaces and foundations.
The city’s rapid growth means a very large share of the housing stock is recent, and recent construction in this climate has a characteristic profile: airtight envelopes, ducted systems in vented attics, and cooling equipment chosen generously. That combination gives you a house that seals well enough to need mechanical fresh air and a system that runs too briefly to dry it. Both halves are fixable, and neither is fixed by adjusting the thermostat.
The rising dew point trend matters for anyone specifying equipment now. A system sized to the conditions of twenty years ago is being asked to remove more water than it was designed for, which is a further argument for separating the two jobs — let the air conditioner handle heat, and give moisture its own machine.
Common questions
Why is my new Austin house more humid than my old one?
Because it is much better sealed and its cooling system is probably larger than it needs to be. The old house leaked continuously, which ventilated it by accident; the new one does not, so the moisture your household produces stays inside. At the same time an oversized system reaches the set temperature quickly and shuts off before it has removed much water. Tight envelope plus short cycles is the standard profile of a clammy new build.
How long should my air conditioner run to control humidity?
Long cycles rather than short ones — as a rough guide, a system that runs 15 to 20 minutes or more at a time on a hot afternoon is removing water, while one that satisfies in 5 to 8 minutes is not. If your cycles are short and the humidity is high, the equipment is oversized for the house, and the fixes are a variable-speed system at replacement time or a dedicated dehumidifier now.
Is the Austin dew point really rising or is that just hotter summers?
It is the dew point specifically, which is a measure of water content rather than temperature. The Austin–San Antonio corridor has seen its warm-season average dew point rise by roughly three degrees over the historical record. That is separate from the temperature trend and it matters more for a house, because dew point is what decides how much water a cooling coil has to condense out.
Do I need a humidifier in Austin?
Only for the handful of freeze weeks, and only if you have timber floors, furniture or instruments you care about, or someone in the house with dry-air symptoms. A single room humidifier with a humidistat set to 40% covers it. Whole-house humidification is hard to justify for a climate that spends five months needing the opposite.
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)