Quick answer
Read in 4 minIn the Ohio Valley, the thermostat lies to you. Our average summer dew point sits near 75°F — which is the moisture line where 72°F on the thermostat still feels sticky, sleep gets worse, and your AC starts short-cycling because it satisfied the temperature before it ever wrung the water out of the air. Indoor relative humidity above 55% is what feeds mold on baseboards, dust mites in mattresses, and that musty basement smell every August. The honest math is that comfort is two numbers, not one: dry-bulb temperature and dew point. An undersized or oversized AC will hit your set point and ignore the second number every time, which is why so many Evansville and Princeton homes feel "cold and clammy" at 70°F.
- 01 Target indoor RH: 45–55% in summer, 30–40% in winter — measured, not guessed.
- 02 SW Indiana summer dew point averages ~75°F; outdoor air at that dew point feels oppressive even at 80°F.
- 03 Oversized ACs cool fast and short-cycle, leaving 60%+ indoor RH and that clammy feel.
- 04 Mold and dust mites thrive above 60% RH; respiratory irritation climbs with both.
- 05 Variable-speed equipment and a properly-sized whole-house dehumidifier solve what a thermostat alone cannot.
Section 02
Why your thermostat keeps lying to you
A thermostat only reads dry-bulb temperature — the heat — and ignores the water in the air entirely. In the Ohio Valley that is the wrong sensor to trust because our summers are defined by moisture, not heat. A 78°F afternoon at 40% RH feels great; the same 78°F at 65% RH feels miserable and your skin can't evaporate sweat. When homeowners tell us they crank the system down to 68°F and still feel sticky, the problem is almost never the temperature — it is that the AC satisfied the thermostat in eight minutes and never ran long enough to remove the latent load. That short-cycle pattern is the single most common comfort complaint we see in Newburgh and Princeton every July.
Section 03
What 75°F dew points actually do to a house
Dew point is the temperature at which water condenses out of the air, and Southwest Indiana sits at a 70–76°F dew point for most of June, July, and August. That moisture loads up everything porous in the house — carpet padding, drywall, baseboards, attic sheathing — and it feeds biology. Mold colonies need about 60% surface RH to grow, dust mites need around 50%, and both populations explode when indoor RH drifts up into the 60s. We have walked basements in Haubstadt where the RH meter pinned at 78% and the homeowner had been wondering for a year why their allergies were worse at home than at work.
Section 04
What we actually see in SW Indiana homes
The pattern is so consistent we can almost predict it from the address: 2010-era builds with a 4-ton single-stage AC on a house that needed 2.5 tons, ductwork undersized for the new equipment, no dehumidifier, and a thermostat in the coolest room of the house. The system runs short cycles, indoor RH lives in the high 50s and low 60s, and the homeowner thinks something is wrong with the unit. Usually nothing is broken — the equipment was matched to the wrong number. A right-sized two-stage or variable-speed system fixes most of it; a dedicated dehumidifier finishes the rest. We have done the same fix on Evansville Lincolnshire ranches and Princeton new-builds and the result is the same: lower set point on the thermostat, lower utility bill, dry air.
Section 05
When humidity is the real problem you're solving
If you set the thermostat at 72°F and still feel clammy, if you have mold on caulk or grout you keep cleaning, if your wood floors cup in summer and gap in winter, if your allergies are worse indoors, if your basement smells musty — every one of those is a humidity symptom, not a temperature symptom. Buying a bigger AC will make the problem worse, not better, because it will short-cycle harder. The answer is almost always longer runtime at lower capacity (variable-speed) plus a dedicated moisture removal strategy. That sequence is what we install when "the AC isn't working" turns out to be the wrong diagnosis.
How it works
The mechanism, explained.
Sensible vs. latent — the two jobs an AC does
Air conditioning does two things at once. Sensible cooling lowers the dry-bulb temperature; latent cooling condenses water on the cold evaporator coil and drains it outside. A correctly sized AC running at lower capacity for a long stretch does both jobs well — coil stays cold, water drips out the condensate line, indoor RH stays near 50%. An oversized AC ramps the coil cold, satisfies the temperature in eight minutes, and shuts off before significant water has condensed. That is mechanically why short cycles produce cold, clammy air. The honest fix is matching equipment capacity to actual load — not the rule-of-thumb the previous installer used.
Why dew point is the number that actually matters
Relative humidity is a ratio that changes with temperature; dew point is an absolute measure of water content. When the weather app says it is 92°F with a 76°F dew point, that air contains a specific amount of water regardless of where you put it. When that air leaks into your house and gets cooled to 72°F, the relative humidity climbs because cool air can hold less water. The point: outdoor dew point tells you the moisture load your AC has to fight, and ours is among the highest in the Midwest from late May through September.
Where the moisture is sneaking in
Even sealed houses leak. Doors open and close, dryer vents pull makeup air through whatever gap they can find, plumbing penetrations move air, and bath fans pull conditioned air out while pulling humid attic air down. Crawlspaces are the biggest culprit in SW Indiana — most of ours are vented, which means in July you are deliberately piping 76°F dew-point air directly under your floor joists. Encapsulating a crawlspace and putting a small dehumidifier in it is one of the most cost-effective comfort upgrades we install, and it usually drops main-floor humidity 5–10 percentage points.
What variable-speed equipment actually changes
A single-stage AC has two settings: off and 100%. A two-stage has off, ~67%, and 100%. A variable-speed inverter can modulate from about 25% to 100% in fine increments. On a mild humid day — say, 78°F with a 72°F dew point — a single-stage runs short cycles all day. A variable-speed system idles along at 35% capacity, keeping the coil cold for hours, draining water continuously. Same set point, dramatically different RH. That is why we recommend variable-speed for almost every Ohio Valley replacement where the homeowner cares about comfort and not just first cost.
Key terms in context
Vocabulary you'll see on a real estimate.
This guide is written for indoor air & comfort decisions in Southwest Indiana. It uses the same terminology you'll hear from techs, inspectors, and the permit office.
Failure mode 01
What goes wrong when humidity gets ignored
Ignoring humidity for a few years costs you in pieces you don't see at first. Wood floors cup, casework joints open, drywall corners get soft, the HVAC closet smells musty, dust mites colonize bedding, and asthma and allergy symptoms creep up. Eventually you find black surface mold on a basement wall and the abatement bill is five figures. None of that is a freak event in our climate — it is what an uncontrolled 60% RH does over four or five Ohio Valley summers. The cheapest version of this problem is the version you catch before drywall and flooring are involved.
Failure mode 02
Buying a bigger AC and making it worse
The single most common mistake we are called to fix is "my old unit couldn't keep up so I had them put in a bigger one." Bigger AC = shorter cycles = wetter house, every time. We have replaced 5-ton systems with right-sized 3-ton variable-speed systems and watched indoor RH drop from 62% to 48% with the same thermostat setting. The honest math is that load calculation (Manual J) is not optional and a rule-of-thumb sizing is how you end up with a clammy house. If a contractor measures your square footage and pulls a tonnage off the ceiling, that is the conversation to walk away from.
Proof, process & local validation
- 01 Every Perfect Climate comfort check includes a calibrated RH and dew-point reading — not just thermostat temperature.
- 02 We run Manual J load calculations before every replacement quote so the equipment matches the house, not a rule of thumb.
- 03 15+ years installing variable-speed systems across the Ohio Valley — and the Google reviews our neighbors leave us tell the story.
How we build this guidance
- We measure RH and dew point on every comfort check — temperature alone misses half the story.
- Pat and the team have commissioned variable-speed systems across Vanderburgh, Gibson, and Warrick counties year after year.
- Perfect Climate has installed whole-house dehumidifiers on homes that "couldn't get comfortable" for years.
Methodology · Perfect Climate validates every humidity recommendation with on-site psychrometric measurements (dry-bulb temp, RH, and dew point) plus a Manual J load calc — not square-foot rules of thumb.
Last updated 2026-06-24
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Common questions
Questions, answered.
01 What indoor humidity level should I aim for in Southwest Indiana?
Aim for 45–55% RH in summer and 30–40% RH in winter. Above 55% in summer is where mold and dust mites thrive and where the "cold and clammy" feeling starts. Below 30% in winter is where static, dry skin, and cracked wood show up. A $15 hygrometer on the kitchen counter is enough to know where you actually live — most homes we measure are nowhere near where the homeowner assumed.
02 Why does my house feel humid even with the AC running?
Almost always because the AC is oversized for the load. It hits the thermostat set point in a few minutes and shuts off before the coil has had time to condense meaningful water. You feel the temperature drop but the moisture stays in the air. Fixing it usually means a right-sized two-stage or variable-speed AC and, on tighter houses or basements, a dedicated dehumidifier. Buying a bigger unit makes it worse.
03 Can I just run a portable dehumidifier instead?
A portable unit will pull moisture out of one room, but it dumps heat back into that room and the basement-sized ones are loud. For a whole house in our climate, a ducted whole-house dehumidifier integrated with your HVAC moves about ten times the air a portable does and operates almost silently. The cost is higher up front but the comfort difference is night and day, particularly in basements and on shoulder-season days when the AC barely runs.
04 Does a smart thermostat help with humidity?
A little — some have a "dehumidify" mode that runs the AC longer to dry the air, but it can only work with what the equipment can do. If the AC is single-stage and oversized, the thermostat is stuck with the same short cycles, just slightly extended. Real humidity control comes from the equipment first, the thermostat second.
05 Is high humidity actually dangerous or just uncomfortable?
Both. Comfort and sleep degrade quickly above 55% RH, and the health risks — mold, dust mites, respiratory irritation, and wood/structural damage — are well documented. We have walked into houses where the homeowner's "allergies" cleared up two weeks after we got the indoor RH under 50% and treated a moldy crawlspace. It is not always the only fix, but it is almost always part of the fix.
