When One PTAC Isn’t Enough — Designing Balanced Heating and Cooling for Weird Floor Plans

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Tony’s Real-World Guide to Multi-Unit Layouts, Hot-Cold Imbalances & Comfort Zones That Don’t Match the Blueprint

Most homeowners think a PTAC is like a magic brick: stick one in a wall and it heats and cools anything you throw at it.

That’s true…
until you try to condition a room that makes no physical sense.

Tony sees it every week:

Long railroad-style rooms
L-shaped studio apartments
Lofts with 14-ft ceilings
Rooms with three exterior walls
Spaces broken up by half-walls, alcoves, or odd geometry
Bedrooms tucked behind closets
Converted garages
Basement apartments with “dead corners”
Motel rooms where the bed area is 20 degrees colder than the kitchenette

These are what Tony calls “weird floor plans” — and they break every rule a normal PTAC sizing chart uses.

In this article, Tony explains how he designs balanced heating and cooling when one PTAC just isn’t enough, how airflow behaves in weird spaces, and why multi-unit zoning is often cheaper and more efficient than forcing a single unit to do the impossible.

🧭 Why Some Rooms Can’t Be Heated or Cooled by One PTAC — Even If the BTUs Match on Paper

You can have the perfect PTAC — like the Amana J-Series 15,000 BTU unit
https://thefurnaceoutlet.com/products/amana-j-series-model-15-000-btu-ptac-unit-with-3-5-kw-electric-heat-ptc153j35axx —
and it still won’t heat or cool a weird space evenly.

Why?

Because PTACs aren’t central air. They’re directional air machines.

They only:

pull room air from an immediate area
blow conditioned air in a fixed direction
condition based on air mixing, not duct distribution

So if the PTAC can’t “see” the area it needs to treat, it can’t control it.

Tony says it best:

“If air can’t flow there, heat and cold can’t follow.”

And weird floor plans break the airflow path.

🏚️ Floor Plans That ALWAYS Need More Than One PTAC

(Tony has never seen these work with a single unit)

These room types guarantee uneven temperatures if you try to cheat with one PTAC.

🏢 1. L-Shaped or “Dog-Leg” Layouts

Air blows straight… not around corners.

If part of the room is hidden behind a wall, that area becomes:

hotter in summer
colder in winter
stale
humid

Like a “dead zone.”

🪟 2. Rooms With Multiple Exterior Exposures

A room with two or three exterior walls experiences wildly different loads depending on:

sun angle
wind direction
wall insulation
window type

One PTAC cannot overcome multi-directional heating and cooling loads.

🧱 3. Long, Narrow “Shotgun” Rooms

Air does not travel 25–30 feet with enough velocity to keep the far end comfortable.

The far end will always drift several degrees.

🛏️ 4. Bedrooms Hidden Behind Hallways, Closets, or Dividers

A PTAC in the living area cannot push conditioned air into a recessed bedroom without ducting (which PTACs don’t have).

🧊 5. Rooms With Lofted or Cathedral Ceilings

Heat rises.
Cold air drops.

A PTAC placed mid-height creates stratification:

80°F at the ceiling
68°F at face height
63°F near the floor

No single PTAC fixes this without destratification fans.

🧩 6. Spaces With High Internal Loads

Examples:

gaming setups
home offices
server nooks
laundry areas
kitchens

Internal heat sources create micro-climates that need their own zone.

🌡️ BTUs Don’t Solve Airflow Problems — They Make Them Worse

This is Tony’s #1 rule for weird floor plans:

“If one PTAC can’t reach the far end, don’t buy a bigger PTAC.
You’ll just freeze one side and cook the other.”

Oversizing causes:

short cycling
humidity problems
coil freeze-ups
electric heat overloads
noise
temperature whiplash

Even ENERGY STAR warns against oversizing room systems

You solve weird floor plans with multi-unit zoning, not brute force.

🌀 How Air Actually Moves in Weird Rooms (Tony’s Field Explanation)

Airflow behaves like water:
It takes the easiest path.

In rooms with obstacles, splits, corners, and long distances:

air slows down
turbulence increases
conditioned air pools in one area
dead zones form
thermostat readings become inaccurate

Tony often uses a simple incense test or fog spray to demonstrate airflow blockage — a practical version of airflow visualization used in ventilation engineering:
https://www.epa.gov/indoor-air-quality-iaq

The results are always the same:

If the air can’t get there, the PTAC can’t condition it.

🧊 Temperature Drift: The Silent Enemy of PTAC Performance

Temperature drift occurs when the PTAC cools or heats the air near the unit much faster than the rest of the room.

Examples Tony sees:

65°F near the PTAC
71°F across the mid-room
78°F in the corner behind a wall

This drift grows worse when:

the PTAC is oversized
the room is long
obstructions are present
airflow pathways are poor
ceiling height increases

ASHRAE identifies stratification and poor mixing as major contributors to comfort imbalance

Tony’s simple fix?

Stop asking one unit to do the job of two.

📐 Tony’s Rule: “If a Room Has More Than One Thermal Load, It Needs More Than One PTAC.”

Thermal load ≠ square footage.
Thermal load = heat coming from:

windows
exterior walls
occupants
appliances
sun angle
ceiling height
insulation gaps
infiltration

If a room has two or more distinct load zones, you must split the system.

🔥 Designing Two-PTAC or Multi-PTAC Systems (Tony’s Blueprint)

Here’s Tony’s exact method for laying out multi-unit PTAC systems.

🧊 Step 1 — Identify Load Zones (Hot, Cold, Blocked, or Exposed)

Tony classifies each section of the room as:

High load (sun, glass, exterior exposure)
Low load (shaded, interior, recessed)
Mixed load

The high-load zone always gets its own PTAC.

🧭 Step 2 — Find the Airflow Path (Or Lack of One)

Tony traces:

airflow direction
blocked pathways
corners
alcoves
elevation changes

Where air stops, the zone ends.

🪟 Step 3 — Match Each Zone to a PTAC Capacity

Examples:

Zone 1 (sun-exposed front area)

10–15k BTU PTAC

Zone 2 (rear bedroom alcove)

7–9k BTU PTAC

🧱 Step 4 — Place Units Facing the Load, Not Each Other

Big mistake Tony sees:
People mount two PTACs on the same wall.

Optimal placement is:

across zones
facing thermal loads
angled to promote mixing
NEVER back-to-back unless rooms are separated

💡 Step 5 — Separate Thermostats = Separate Comfort

Each PTAC gets:

its own thermostat
its own fan mode
its own schedule

This avoids “fighting” systems.

🔥 Step 6 — For Heating, Consider Electric Heat Capacity Carefully

When using units like the Amana J-Series, heat kit selection makes or breaks comfort:

3.5 kW for small zones
5 kW for high-loss exterior areas
Dual-stage for mixed or unpredictable zones

More on electric heat design:
https://www.energy.gov/energysaver/electric-resistance-heating

🧰 Tony’s Real-World Scenarios (And the PTAC Layouts He Designed)

Below are REAL situations Tony has solved.

🏙️ SCENARIO #1 — Long Studio Apartment (30 ft Narrow Layout)

Symptoms:

Kitchen end: hot
Bed area: cold
PTAC: short cycling
Humidity high

Tony’s fix:

PTAC #1: 12k BTU near the kitchen
PTAC #2: 7k PTAC near the bed area
Independent thermostats
Slight offset cooling stages

Result:
Perfectly balanced air, no drift, lower bills.

🛏️ SCENARIO #2 — Bedroom Behind 10-Foot Hallway

No PTAC could push air around the bend.

Fix:

Small 9k PTAC in bedroom zone
12k PTAC in main living area
Door undercut for passive return

🪟 SCENARIO #3 — Sunroom + Interior Living Area

Sunroom had massive glass load.

Fix:

15k PTAC for sunroom
9k PTAC for interior room
Dehumidification priority in sunroom

🧱 SCENARIO #4 — Basement Apartment With “Dead Corner” Office

Corner office always cold.

Fix:

7k PTAC installed directly in the office
Main PTAC serves living + kitchenette

Temperature balanced within 1° everywhere.

🏢 SCENARIO #5 — Commercial Office With Cubicles

Cubicle walls blocked airflow.

Fix:

Two 12k PTACs placed at opposite ends
Airflow paths mapped
Return air kept open at cubicle bases

🧊 Why Multi-Unit PTAC Systems Often Use LESS Energy Than One Oversized Unit

It sounds backwards — more units but lower bills.

Here’s why:

1. Each unit runs only as needed

Zones with lower loads barely run.

2. Smaller units run longer cycles (higher efficiency)

Short cycling kills efficiency.

3. Heat kits don’t slam on all at once

This improves electric heat performance.

4. Temperature setpoints can vary by zone

People rarely want every area at the same temperature.

5. Lower fan speeds mean quieter operation and lower wattage

💥 The Hidden Cost of Forcing One PTAC to Do the Job of Two

Tony has replaced hundreds of prematurely failed units caused by “single-unit stubbornness.”

Problems include:

overheated compressors
electric heat burnout
warped sleeves
mold buildup from short cycling
constant thermostat complaints
unbalanced humidity
customer refunds in hotels and rentals

The cost of a second PTAC is nothing compared to:

high electric bills
shortened equipment lifespan
poor guest reviews
constant hot/cold complaints

📝 Tony’s Checklist: When You MUST Add a Second PTAC

If ANY of these are true, you need two (or more) units:

The room is longer than 22 feet
There’s an L-shape or alcove
There are two+ exterior walls
Ceiling height exceeds 10 feet
Temperature drifts more than 3°F
You have a sunroom or glass-heavy area
A bedroom is hidden behind another space
The internal load (computers, appliances) is high
Humidity differs across the room
The PTAC frequently short cycles

If two or more are true?
A single PTAC has no chance.

🏁 Final Word — When One PTAC Isn’t Enough, Don’t Ask It to Be a Hero

Weird floor plans aren’t a mistake — they’re just not designed for single-point heating and cooling.

Tony’s rule:

“It’s not about BTUs.
It’s about where the BTUs need to GO.”

One PTAC can’t:

push air around corners
overcome multiple thermal loads
condition long distances
fix dead zones
balance temperature across complex rooms

But two right-sized PTACs can:

reduce energy bills
increase comfort
eliminate hot/cold spots
improve humidity control
extend equipment life
stop short cycling
provide true zoning

The right number of PTACs is the number the ROOM demands — not the number on your wall budget.

Buy this on Amazon at: https://amzn.to/47cH9ut

In the next topic we will know mmore about: Why Voltage, Amps, and Wire Gauge Matter More Than BTUs - Tony’s Electrical Reality Check Before You Install a 15k PTAC

Tags: Tony’s toolbox talk

WRITTEN BY

Tony Marino

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