Why Some Rooms Will Never Stay Warm Without Backup (No Matter How Many BTUs You Throw at Them)
When winter hits hard, every PTAC eventually hits a wall.
Most homeowners blame the PTAC:
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“It’s not heating enough.”
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“It ran all night and the room is still freezing.”
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“The thermostat never moves.”
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“My electric bill is insane.”
Tony has a simpler explanation:
“PTACs are NOT furnaces.
They’re not mini splits either.
Every PTAC has a hard limit — and winter will expose it.”
There are specific conditions where a PTAC cannot heat the space on its own, no matter what size you buy.
In these rooms, Tony automatically adds supplemental heat: electric baseboard, radiant panels, kickspace heaters, in-wall heaters, or even a small portable system.
Amana J-Series PTAC Model 15,000 BTU PTAC Unit with 3.5 kW Electric Heat
This guide breaks down Tony’s full list of scenarios where supplemental heat isn’t optional — it’s required — along with his sizing method, warning signs, and fix strategies.
🔥 Why PTAC Heat Output Is Deceptive (The Hidden Physics Tony Looks At)
PTACs heat using:
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Heat pump mode (efficient, but limited in cold weather)
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Electric heat strip mode (powerful, but expensive to run)
But homeowners misunderstand the numbers.
A PTAC labeled “15,000 BTU with 3.5 kW heat” doesn’t mean:
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it always outputs 15k
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it always delivers 3.5 kW
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it can overcome structural heat loss
In reality:
✔ Heat pump BTUs collapse in low outdoor temps
Heat pumps lose efficiency below ~35°F.
DOE cold-climate performance chart:
https://www.energy.gov/energysaver/heat-pump-systems
✔ Electric heat strips draw huge amps
3.5 kW = ~12,000 BTUs
5.0 kW = ~17,000 BTUs
7.0 kW = ~24,000 BTUs
But they cost MUCH more to run.
✔ PTACs are designed for mild winter heating
They’re made for bedrooms, hotel rooms, office spaces — not harsh winter climates or high heat-loss spaces.
Tony says:
“PTACs keep you warm.
They don’t fight winter for you.”
That’s where supplemental heat comes in.
🧊 When Heat Pumps Stop Helping — The Cold-Weather Drop-Off Curve
Heat pump output falls as outdoor temps drop.
Typical PTAC heat pump capacity:
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100% at 47°F
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70% at 35°F
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40–55% at 25°F
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0–20% at 5–10°F
Below 35°F, Tony assumes:
“The heat pump is decorative. The electric heat strip is doing all the work.”
That’s why many PTACs hit their limit long before the thermostat does.
🏡 The 11 Scenarios Where Tony ALWAYS Adds Supplemental Heat
Tony has seen thousands of rooms across hotels, condos, offices, rentals, basements, garages — and these are the ones where PTACs always struggle.
🧱 1. Rooms With High Heat Loss Through Exterior Walls
(Brick, block, metal stud, or poorly insulated walls)
Walls that leak heat faster than BTUs can replace it will ALWAYS overload a PTAC.
ASHRAE shows how heat loss varies by wall type:
https://www.ashrae.org/technical-resources/ashrae-handbook
Add supplemental heat if the room has:
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block walls
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uninsulated brick
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metal stud framing
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cracked stucco
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old plaster with no cavity insulation
🪟 2. Rooms With Large or Leaky Windows
Especially:
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slider windows
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old aluminum frames
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west-facing glass
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drafty windows
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thin double-pane units
Big glass + winter = heat loss monster.
Supplemental heat required.
🧊 3. Rooms Below Grade (Basements)
Basements stay:
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colder
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damp
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harder to heat
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more conductive
PTACs struggle because ground-contact walls drain heat relentlessly.
Tony always adds:
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radiant wall panels
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electric baseboard
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or a second heat source
🏢 4. Corner Rooms, End Units & Rooms With Two Exterior Walls
These rooms lose heat from multiple sides and experience:
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cross winds
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pressure imbalance
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extreme temperature swings
Hotels deal with this constantly.
Tony says:
“If you have two outside walls, you need two heat sources.”
🏠 5. Rooms Over Garages, Porches, or Crawlspaces
If the floor is cold, the room is cold.
PTACs struggle to fight downward heat loss.
Supplemental heat is mandatory beneath:
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cold floors
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hollow floor cavities
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slab-on-grade transitions
❄️ 6. Rooms in Cold Climates (Winter lows below 25°F)
Below 25°F:
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heat pump capacity collapses
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electric strips become the ONLY heat source
But electric strips alone often cannot keep up.
Tony supplements ANY PTAC installation in:
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New England
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Upper Midwest
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Mountain states
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Northern plains
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Canada-border regions
🏚️ 7. Drafty Rooms With Uncontrolled Air Leaks
PTACs cannot heat a room that leaks cold air faster than they can warm it.
Air leaks = unresolvable without help.
EPA air sealing guide:
https://www.epa.gov/indoor-air-quality-iaq/
If Tony sees:
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light under the door
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draft near outlets
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gaps around the sleeve
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leaky exterior penetrations
He adds supplemental heat.
🚪 8. Rooms With High Ceilings (10 ft +)
Heat rises.
PTAC heat output stays near the floor.
Large volumes demand additional heat sources, especially radiant heat.
Tony says:
“If the ceiling is tall, the room is cold.”
🚿 9. Rooms With High Moisture Loads (Bathrooms, Spa Areas)
Humidity chills the room by:
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absorbing heat
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increasing latent load
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making PTACs work harder
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dropping coil temps
Moisture steals BTUs.
Supplemental heat keeps temps stable.
🛏️ 10. Rooms With Oversized PTACs (Yes — Too BIG Creates Heating Problems)
Too big → short cycles → no heat buildup → cold room.
An oversized PTAC actually reduces heating output because it:
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shuts off too quickly
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doesn’t run heat strips long enough
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misreads thermostat temps
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never equilibrates
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fails to warm the structure
Tony fixes this with supplemental heat.
🧍♂️ 11. Rooms With High Occupancy or High Heat Demand
More people = more heat in cooling mode, but worse performance in heating mode.
Why?
Because body moisture raises latent load — harder for the heat pump to operate efficiently.
Tony adds supplemental heat for:
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offices
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classrooms
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hotel suites
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meeting rooms
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small commercial spaces
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coworking rooms
🔥 Tony’s 3 Heat Types — and When He Uses Each
Tony picks supplemental heat depending on the room’s weaknesses.
🔌 1. Electric Baseboard Heat
✔ Silent
✔ Steady
✔ Good for cold climates
✔ Works when PTAC shuts off
Best for:
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corner rooms
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drafty rooms
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cold floors
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high ceilings
🌞 2. Electric Radiant Wall or Ceiling Panels
✔ Doesn’t rely on air
✔ Heats objects directly
✔ Fixes cold-wall problems
Used when:
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walls leak heat
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BTUs can’t overcome mass loss
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rooms feel cold at same temperature
🌬️ 3. Small In-Wall or Kickspace Heaters
✔ Quick heat
✔ Compact
✔ Cheap
Best for:
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bathrooms
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entryways
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small offices
📏 Tony’s Supplemental Heat Sizing Formula
Tony doesn’t guess.
He calculates the deficit.
Step 1 — Identify heat loss
(Tony uses ASHRAE charts + wall condition + climate zone)
ASHRAE heating load reference:
https://www.ashrae.org/technical-resources/ashrae-handbook
Step 2 — Compare it to PTAC deliverable BTUs
Heat pump BTUs collapse in the cold.
Electric strip BTUs depend on power input.
Step 3 — Identify the deficit
Example:
Room needs: 18,000 BTU/h
PTAC provides: 12,000 BTU/h (heat strip)
Deficit: 6,000 BTU/h
Step 4 — Add supplemental heat covering at least the deficit
Tony always overshoots by +10–20%.
🚨 Tony’s Warning Signs That a Room Needs Supplemental Heat
If ANY of these occur, Tony adds backup heat.
🔻 1. PTAC runs nonstop in winter
This is the #1 giveaway.
🔻 2. Room never reaches setpoint
Doesn’t matter if PTAC is new — it’s undersized for the wall conditions.
🔻 3. Electric bill skyrockets in winter
Heat strips are in full-time emergency mode.
🔻 4. Coil frost or heat pump defrost cycles constantly
Heat pump is maxed out.
🔻 5. Temperature stratification (warm ceiling, cold floor)
High ceilings or poor air circulation.
🔻 6. Room gets cold after sundown
Indicates high thermal mass walls losing stored heat.
🔻 7. PTAC short cycles in heating mode
Oversized unit → no steady heat buildup.
🔻 8. Heat kit trips breaker or high-limit switch
Airflow is inadequate for the load.
Room needs more heat sources.
🧪 Real Case Studies (Tony’s Field Notes)
These are situations Tony sees multiple times EVERY winter:
🏨 Hotel End Unit — 15k PTAC Can’t Hold 70°F at Night
Fix: Added 1,500W baseboard → problem gone.
🏠 Basement Rental — PTAC Runs 24/7 in January
Fix: Added radiant ceiling panel → humidity drop + stable heat.
🧱 Brick Apartment — Heat Loss Too Large
Fix: Added 2kW in-wall heater → stable temp even at 20°F.
🏢 Corner Office — PTAC Short Cycling
Fix: Added mini panel heater under desk → even temperatures for entire room.
🧠 Tony’s Golden Rule:
“A PTAC isn’t a heating system.
It’s one PART of a heating system.”
Supplemental heat isn’t a failure — it’s a blueprint.
When you add backup heat correctly:
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PTAC lasts longer
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bills drop
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comfort increases
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thermostat stabilizes
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humidity improves
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freeze risk falls
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heat kit stays healthy
Your PTAC performs like it’s supposed to — without being asked to do the impossible.
🏁 Final Word — If the Room Beats the PTAC, You Must Add Heat
If the room:
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leaks heat
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has bad walls
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faces extreme weather
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has high ceilings
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suffers cold floors
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contains large glass
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or drops below freezing
Then no PTAC on earth can heat it alone.
Tony’s final say:
“You don’t fix a cold room with a bigger PTAC.
You fix a cold room with more heat sources.”
That’s why supplemental heat isn’t optional — it’s the difference between:
❌ a system that struggles
and
✔ a system that actually heats the room comfortably.
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In the next topic we will know more about: Why the Room Controls the System — Not the Other Way Around. How Tony Sizes PTACs by Load Shape, Not Square Footage Numbers That Lie
