Most homeowners in humid climates think cooling is cooling.
Drop the temperature, kick on the AC, and the room feels better.
But Tony knows something most people don’t:
“In humid climates, cooling the AIR is easy.
Removing the WATER is the real job.”
If a PTAC can’t pull moisture out of the air fast enough, the room will:
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feel clammy
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never hit the real comfort point
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grow mildew
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smell musty
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fog the windows
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run longer cycles
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freeze the coil
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overheat the compressor
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chew up electricity
This is why Tony does NOT rely on BTUs alone in humid climates.
He sizes based on the sensible vs. latent split — the real measure of how well a PTAC handles both temperature and moisture.
Amana J-Series PTAC Model 15,000 BTU PTAC Unit with 3.5 kW Electric Heat
Through-the-wall PTACs are fantastic machines…
But in high humidity environments, they have limits.
And if you ignore the physics, the room will fight you all summer long.
This article reveals Tony’s humidity-first approach, the science behind sensible vs. latent heat, and why your PTAC’s moisture removal rating matters more than its BTU number.
💧 The Hard Truth: Humidity Is Half the Cooling Load (Sometimes More)
In dry climates, most of the PTAC's job is sensible cooling — lowering air temperature.
But in humid climates?
Up to 50%–70% of the cooling load is latent — moisture removal.
Meaning:
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A 12,000 BTU PTAC might only give you 6,000–7,000 BTUs of actual temperature cooling
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The rest of its output is battling moisture
This is documented in ASHRAE’s fundamentals of HVAC design:
https://www.ashrae.org/technical-resources/ashrae-handbook
If your PTAC isn’t designed to handle humidity, or you choose the wrong unit, it doesn’t matter how many BTUs you buy — the air never feels dry, cool, or comfortable.
Tony’s rule:
“In humid climates, your PTAC is a dehumidifier first and an AC second.”
🌡️ Sensible vs. Latent Heat — Tony’s Simple Explanation
Tony likes to explain it this way:
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Sensible heat = thermostat heat (temperature you can “sense”)
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Latent heat = moisture load (humidity you can’t see but definitely feel)
Your PTAC must remove BOTH.
Sensible Cooling
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Drops the air temperature
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Measured in BTUs
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Thermostat reacts to this
Latent Cooling
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Removes moisture
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Not shown on most spec sheets
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Requires slower airflow & colder coil temps
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Only measured through humidity performance
The DOE summarizes this well here:
https://www.energy.gov/energysaver/room-air-conditioners
If your PTAC only handles sensible heat well, the room will feel sticky — even if the thermostat says 70°F.
This is why Tony sizes PTACs using splits, not just BTUs.
🔍 What Is the Sensible Heat Ratio (SHR)? Why Tony Cares So Much
SHR tells you what percent of the AC’s performance goes toward sensible cooling.
SHR = Sensible Cooling ÷ Total Cooling
Example:
A PTAC has:
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9,000 BTU sensible
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3,000 BTU latent
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12,000 BTU total
SHR = 0.75 (75% sensible, 25% moisture)
This unit is decent for humid climates.
But many PTACs have SHR values around 0.85–0.90 — bad for moisture control.
Tony refuses to install those near the Gulf Coast, Southeast, Midwest summers, or anywhere that gets humidity spikes after rainfall.
The HVAC industry uses SHR to evaluate equipment load match:
https://www.ahrinet.org/
Failing to check SHR is how you get:
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sticky rooms
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moldy smells
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freeze-ups
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sweaty windows
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sky-high electric bills
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non-stop complaints
Tony calls high-SHR through-the-wall units:
“Temperature machines, not comfort machines.”
🧊 Why Through-the-Wall Units Struggle in Humid Climates
PTACs and through-the-wall ACs have unique challenges:
🪟 1. They pull in unconditioned outdoor air
Outdoor humidity skyrockets the latent load.
🌀 2. Their evaporator coils are smaller than central air
Smaller coils = less moisture removal capacity.
🚫 3. They often run high airflow by default
High CFM = less latent removal
(air passes over the coil too fast to condense moisture)
🧱 4. Poorly installed sleeves leak humidity from outside
Humidity enters before you even turn the unit on.
The DOE covers the importance of sealed installation
🌡️ 5. They shut off too early due to thermostat misread
If the return air stays cool but humid air pools elsewhere → short cycling.
💥 The Silent Killer: High Airflow (CFM) in Humid Climates
Too much airflow = not enough moisture removal.
Tony explains it like this:
“In humid places, fast air is the enemy.
You want slow, cold coil contact to strip out moisture.”
High airflow causes:
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weak dehumidification
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clammy output
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coil temperatures rising
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freeze-ups when airflow is restricted
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poor distribution
Tony ALWAYS sets PTAC fans to low in humid climates.
🧰 Tony’s Sensible-Latent Sherlock Checklist (The 3 Numbers He Checks Before ANY Install)
Before choosing BTUs, Tony checks:
🔹 1. Local outdoor dew point averages
Dew point matters more than temperature.
If dew points run above 70°F, Tony increases latent capacity requirements.
Weather dot gov dew point reference:
https://www.weather.gov/arx/why_dewpoint_vs_humidity
🔹 2. Room load profile (glass, exposure, occupancy)
Humidity skyrockets with:
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west-facing glass
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multi-occupant rooms
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cooking appliances
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showers
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pet areas
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laundry nearby
🔹 3. PTAC SHR rating (manufacturer spec sheet)
Tony checks the unit’s SHR before BTUs.
Ideal SHR in humid climates:
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0.65–0.75 = excellent
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0.75–0.80 = acceptable
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0.85+ = bad for humidity
If SHR is too high, Tony downsizes airflow or changes the PTAC model altogether.
🧊 How Humidity Creates Freeze-Ups (Even on New PTACs)
Freeze-ups happen when:
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high humidity + high airflow + short cycling
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coil surface temp drops below 32°F
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moisture freezes instead of condensing
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blockages reduce airflow
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coil temperature drops further
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the entire evaporator becomes a block of ice
Tony knows that freeze-ups aren’t refrigerant problems.
They’re airflow and humidity problems.
🧂 Salt Air + Humidity = PTAC Death
Near coastal areas, humidity carries salt particles.
Salt + moisture creates:
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corrosion
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coil leaks
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capacitor failures
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deteriorated wiring
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stuck fan motors
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compressor death
These climates require:
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special protective coatings
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higher moisture removal
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more frequent cleaning
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corrosion-resistant units
The EPA explains salt air corrosion factors:
https://www.epa.gov
Tony refuses to install standard PTACs right next to the coast.
🧭 Tony’s Airflow-First Installation Rules in Humid Climates
This is Tony’s actual field checklist.
🌬️ Rule #1 — Always Use “Low Fan” Mode
Low fan = colder coil = more condensation = more dehumidification.
🧽 Rule #2 — Clean the coil AND remove bio-film
Humidity feeds bio-growth.
Bio-film insulates coils and reduces moisture removal.
Tony says:
“If the coil isn’t shiny, it isn’t doing its job.”
The DOE covers AC coil cleaning guidelines:
https://www.energy.gov/energysaver/maintaining-your-air-conditioner
🧱 Rule #3 — Perfectly seal the sleeve
Humidity leaks ruin latent performance.
Tony seals:
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top
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bottom
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sides
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around the wall sleeve
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outdoor grill
❄️ Rule #4 — Avoid oversized units
Oversizing = short cycling = humidity stays high.
🌡️ Rule #5 — Set a higher temp but lower humidity
Tony often sets PTACs to:
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72–74°F cooling
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Dry mode (if available)
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Continuous low fan
Feels colder than 68°F if humidity drops below 50%.
🛠️ Rule #6 — Angle the unit for proper drainage
If condensate doesn’t drain properly, moisture re-evaporates into the room.
Tony always ensures:
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sleeve angle
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drain path
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outdoor pitch
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clear weep holes
Improper drainage is why many PTACs recirculate humidity.
🏚️ The 6 Common PTAC Failures in Humid Climates — And Why They Happen
Tony lists them:
❄️ 1. Coil Freeze-Ups
Caused by poor airflow + high humidity.
😓 2. Sweating/Condensation on Grilles
Result of poor latent performance.
💧 3. Water Dripping Indoors
Caused by improper sleeve pitch or clogged drains.
🦠 5. Musty Odors or Moldy Smells
Humidity + biofilm on coils + low airflow.
🔊 6. Loud Units (Fan Fighting Moisture)
Fans struggle against saturated coils.
🧠 Tony’s Golden Rule for Humid Climates
“In dry places, size for BTUs.
In humid places, size for SHR.”
Meaning:
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BTUs determine temperature
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SHR determines comfort
A room at 74°F with 45% humidity feels amazing.
A room at 68°F with 70% humidity feels miserable.
Humidity wins every time.
🏁 Final Word — If You Ignore Humidity, You Haven’t Installed a System. You’ve Installed a Problem.
Through-the-wall cooling works GREAT in humid climates…
As long as you size for humidity, not just heat.
If you get the SHR, airflow, sleeve sealing, and drainage right, your PTAC will:
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cool quickly
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remove moisture aggressively
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prevent freeze-ups
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smell clean
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run quieter
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last longer
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cost less to operate
If you ignore humidity?
You get:
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clammy rooms
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frozen coils
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constant complaints
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mold buildup
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high energy bills
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dead equipment
Tony’s final truth:
“In humid climates, the thermometer lies.
The humidity tells the real story.”
Buy this on Amazon at: https://amzn.to/47cH9ut
In the next topic we will know more about: How Tony Uses Temperature Split to Confirm a PTAC Was Installed Right
