When One Unit Isn’t Enough Signs You Should Zone with Multiple PTACs

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Let me start with the truth I tell homeowners every week:

👉 **Most comfort problems aren’t caused by the PTAC you bought…

they’re caused by the one PTAC you’re trying to make do too much.**

PTACs are room conditioners.

Amana J-Series PTAC Model 17,000 BTU PTAC Unit with 5 kW Electric Heat

They’re designed to give perfect comfort inside a defined space — not stretch themselves across a full apartment, a long open-concept living room, or a garage conversion with multiple “temperature personalities.”

But homeowners constantly ask them to do exactly that.

One PTAC can work flawlessly in a hotel room, bedroom, office, or studio… but when you try to make it cover a hallway, a second bedroom, or two opposite-facing rooms with different sun exposures?

It fails.
Not because it’s weak.
But because the space is asking for zoning, not brute force.

Hotels have known this for decades — they zone aggressively with one PTAC per room.
Homeowners often try to “cheat” with one big unit, and comfort always suffers.

This article breaks down the real signs you need two (or more) PTAC units, why zoning beats oversizing every time, and how to design a zoning layout that gives you hotel-grade comfort at home.

Let’s dive in.

🧩 1️⃣ Why Zoning Matters (And Why Oversizing One PTAC Isn’t the Answer)

Here’s a mistake I see constantly:

“Tony, the living room and bedroom get warm. I think I just need a 15,000 BTU unit.”

Wrong.

When one unit is trying to heat or cool multiple enclosed or semi-enclosed spaces, you get:

uneven temperatures
humidity pockets
comfort imbalances
short cycling
hot/cold corners
wasted energy

Why?

Because PTAC airflow is directional, not whole-house.
It pushes air into the space it faces… not around corners, down hallways, or behind partial walls.

Oversizing a single PTAC creates NEW problems:

❌ Short cycling

The unit cools the main area too fast but never reaches deeper rooms.

❌ High humidity

Quick cooling = poor moisture removal.

❌ Noisy operation

Oversized units cycle loudly and frequently.

❌ Wasted energy

Systems cycle on/off repeatedly.

❌ Cold spots and hot pockets

Air doesn’t mix evenly.

Hotels stopped oversizing decades ago.

They install one PTAC per zone — every room, every suite, every thermal personality gets its own device.

That’s zoning.

🧊 2️⃣ The #1 Sign You Need Multiple PTACs: Temperature Differences Across the Space

Here are the temperature difference complaints I hear every week:

“The living room is freezing but the bedroom is still warm.”
“The front half of my bonus room is cool, but the back half is muggy.”
“My garage is cool, but the attached office is hot.”
“I cool the bedroom fine, but the hallway and bathroom stay warm.”

These are classic signs the PTAC airflow isn’t reaching the entire space.

Why?

✔️ Airflow drops dramatically after 10–15 feet

PTACs aren’t jet engines — they’re designed for balanced room circulation.

✔️ Air doesn’t turn corners

A PTAC can’t push air around a hall corner or behind a wall.

✔️ Rooms have microclimates

Different materials, insulation, and exposures create different heat loads.

✔️ Closed doors = instant zoning

Bedrooms and offices act like separate zones when doors are shut.

If one part of the space is comfortable and another is not, zoning is the fix.

🌞 3️⃣ Sun Exposure Creates Two Different Thermal Personalities in the Same Space

One side of your room bakes.
The other side freezes.

Sound familiar?

Sun exposure is one of the biggest — and most ignored — factors in system sizing.

EnergyStar explains how solar load dramatically affects HVAC performance:

Here’s what I see:

☀️ West-Facing Zones

Afternoons feel like a greenhouse.

❄️ North-Facing Zones

Always cooler. Harder to heat in winter.

🌅 East-Facing Zones

Warm early, stable by afternoon.

🌇 South-Facing Zones

Consistent heat gain most of the day.

When one space contains two competing sun exposures, a single PTAC can never balance both.

That’s a textbook zoning situation.

🏠 4️⃣ When Should You Add a Second PTAC Instead of Upsizing the One You Have?

Here’s the rule:

👉 **If you’re thinking of going bigger than 15,000 BTUs…

you probably need zoning instead.**

Why?

Because 15k is about the limit before airflow becomes too directional and overpowering for a single unit.

Add a second unit if:

✔️ The space has multiple enclosed rooms

(e.g., living room + bedroom)

✔️ One area needs cooling while another needs heating

(extremely common)

✔️ The total square footage exceeds ~600 sq ft

PTAC airflow can’t distribute evenly past this point.

✔️ You have two drastically different sun exposures

(shade vs. direct sunlight)

✔️ One unit is currently running constantly

A sign of oversaturation.

✔️ Noise matters

Two small units are MUCH quieter than one giant, roaring, oversized PTAC.

Upsizing rarely works.
Zoning almost always does.

🛏️ 5️⃣ Room Layouts That Almost Always Need Multi-Zoning

These layouts are notorious troublemakers.

🌀 L-Shaped Rooms

Airflow gets “stuck” in the short leg of the L.

🧱 Bonus Rooms Over Garages

High heat gain + poor insulation.

🪜 Converted Attics

Uneven ceilings create hot pockets.

🏚️ Finished Basements

Cold zones + humidity zones = competing needs.

🧩 Airbnb Suites or Guest Spaces

Guests close doors → instant zoning.

🏢 Office + Bedroom Combo Rooms

Electronics heat up the office; bedroom stays cooler.

🛋️ Long Living + Dining Room Runs

The far end never matches the PTAC end.

🔧 Garage Conversions

Garage → office combos behave like two different planets.

These layouts almost always benefit from two smaller PTACs instead of one big one.

🧮 6️⃣ Tony’s Two-Unit Sizing Formula (Easy & Accurate)

When zoning with two PTACs, don’t size for the whole space. Size for each zone individually.

Here’s the formula I use on every job site:

STEP 1 — Break the space into zones

Example: Living room zone + bedroom zone.

STEP 2 — Size each zone separately

20 BTUs per sq ft per zone.

STEP 3 — Add 10–20% BTUs if that zone has heavy sun exposure

Direct sun → add more cooling.

STEP 4 — Add 600 BTUs per frequent occupant

People add heat.

STEP 5 — Add 15% if the zones are separated by doors

Closed doors = real thermal separation.

STEP 6 — Add 10% for upstairs zones

Heat rises.

STEP 7 — Never oversize either unit more than ONE BTU class

Avoid short-cycling and humidity issues.

Example

450 sq ft living room + 200 sq ft office.

Living Room:

450 × 20 = 9,000 BTUs
+10% for west sun = 9,900
Round to 10,000 BTUs

Office:

200 × 20 = 4,000 BTUs
+600 for occupant = 4,600
Round to 5,000–6,000 BTUs

Total needed = two units, not one 15k.

🔌 7️⃣ Electrical Considerations—You Might Already Be Wired for a Second PTAC

A huge surprise for homeowners:

⚡ Many houses already have unused 208/230V lines.

Often:

old AC closet circuits
former electric heater circuits
capped lines behind drywall
panel space available for a new breaker

Hotels run every PTAC on a dedicated 230V or 265V line.
Homeowners can use the exact same technique.

Here’s what you need for proper zoning:

dedicated circuit
correct voltage (115V or 230V)
correct breaker (15A, 20A, 30A)
correct wire gauge

Electrical load guides are outlined in Energy.gov’s HVAC efficiency guidance:
🔗 https://www.energy.gov/energysaver/air-conditioning

Zoning usually requires LESS electrical demand than running one oversized system at max capacity all day.

💧 8️⃣ Humidity Behavior: Why Zoning Works Better in Hot & Humid Climates

Oversized units cool the air quickly but don’t run long enough to remove humidity.

Two right-sized units:

run longer,
extract more moisture,
maintain stable humidity,
avoid clammy conditions,
reduce mold risk.

This is why multi-unit zoning is so effective in:

Florida
Louisiana
Texas Gulf Coast
Georgia
Carolinas

Humidity load matters as much as temperature load — often more.

🔥 9️⃣ Heating Behavior: Why Winter Makes Zoning Even MORE Important

Cooling problems are annoying.
Heating problems are miserable.

Here’s what happens in winter with one oversized unit:

Heat rises to the wrong zone (often the attic zone).
Rooms with two exterior walls lose heat rapidly.
Zone farthest from PTAC stays cold.
Thermostat installed near the PTAC misreads the room.

Two-zone setups let each area:

heat independently,
compensate for heat loss,
handle exterior walls differently,
warm up evenly in the morning.

Energy.gov explains how heat pumps struggle in cold zones, making zoning even more critical:
🔗 https://www.energy.gov/energysaver/heat-pump-systems

🛠️ 🔟 When Tony Recommends Zoning Automatically

These are my “no questions asked” zoning triggers:

✔️ Room or space bigger than 600 sq ft

PTAC airflow can’t cover it.

✔️ Two or more separate rooms with doors

Bedroom + hall + bath = multiple zones.

✔️ Bonus room over garage

Needs its own zone 99% of the time.

✔️ Finished attic

Ceiling slopes create pocket zones of heat.

✔️ Basement guest suite

Cold & humid → needs its own PTAC.

✔️ West-facing glass wall

Sunload too strong for a single unit.

✔️ Airbnb or guest suite

Guests shut doors → zoning required.

✔️ Office + bedroom combo

Split personality heat load.

✔️ Rooms with drastically different insulation

Old part of home + new addition = separate zones.

If any of these describe your home, one unit will never perform as well as two.

🧠 11️⃣ Tony’s Practical Advantages of Zoning (That You Feel Immediately)

Zoning gives you benefits you notice instantly:

🌡️ 01. Balanced temperatures

No hot/cold pockets.

💧 02. Better humidity control

Units run longer, remove more moisture.

🛌 03. Quieter operation

Two small units are quieter than one oversized beast.

⚡ 04. Lower energy bills

Right-sized units cycle efficiently.

🩺 05. Longer equipment life

Units aren’t pushed beyond their intended capacity.

🔥 06. Better heating in winter

Zones heat independently and evenly.

🌬️ 07. Consistent comfort no matter the layout

Hallways, corners, and back rooms stay conditioned.

🧩 08. Flexibility

Turn off zones you’re not using to save energy.

🛠️ 09. Hotel-grade performance

This is EXACTLY how hotels achieve consistent comfort across rooms.

🏁 12️⃣ Tony’s Final Take

“When your space has two personalities — hot and cold, sunny and shaded, open and closed off — you need two PTACs, not one bigger one.
Zoning isn’t overkill. It’s smart engineering. It’s how you get hotel-level comfort at home.”

One oversized PTAC will always struggle to balance a multi-zone space.
Two right-sized PTACs will always outperform one large one — with better comfort, better humidity control, better heating, and higher efficiency.

Hotels solved this decades ago.
Now homeowners can steal their secret.