If you’ve ever used a PTAC (Packaged Terminal Air Conditioner) during a cold winter, you already know something a lot of homeowners don’t:
👉 Cooling is easy. Heating is the real test.
A PTAC cooling cycle runs efficiently in almost every climate.
Heating? Totally different story.
That’s why PTAC manufacturers build units with electric heat add-ons — 2.5 kW, 3.5 kW, 5 kW, sometimes even 7 kW for heavy-duty northern climates.
And if you’ve been browsing PTAC models, you’ve probably wondered:
“When do I actually need more than a standard 3.5 kW heat kit?”
“Is upgrading to a 5 kW heat kit worth it?”
“Will my electrical panel even support it?”
In this guide, I’m breaking down—plain and simple—everything you need to know about PTAC electric heat kits, how they work, how much heat they really put out, and how to choose the right wattage based on your climate, insulation, room size, and heating expectations.
By the time you’re done reading this, you’ll know exactly when to step up from a 3.5 kW heat kit to a 5 kW model — no guesswork, no overspending, and no waking up freezing at 3 AM.
Let’s get into it.
🔧 1️⃣ What an Electric Heat Kit Actually Does (No Jargon, Just Truth)
Let’s start with the basics — because this is where homeowners get confused.
Every PTAC has two possible heat sources:
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A heat pump
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An electric resistance heater (“heat kit”)
Most PTACs have both.
🌡️ Heat Pump (Primary)
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Works like a standard mini split
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Very efficient
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Struggles below ~40°F
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Slows down dramatically around freezing
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Drops most of its output near 20–25°F
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Near-zero output below ~10°F
🔥 Electric Heat Kit (Backup & Booster)
This is the “heat strip” inside the PTAC.
It uses electric resistance coils — think giant toaster elements — to produce pure heat.
The wattage of that heat kit determines how much heat it can deliver per hour.
🔥 2️⃣ Converting kW to BTUs (The Only Formula You Need)
You don’t need to know electrical engineering.
You just need ONE simple formula:
🔢 1 watt = 3.41 BTUs
Now let’s convert the common heat kits.
| Heat Kit | Wattage | BTUs Produced |
|---|---|---|
| 2.5 kW | 2,500 watts | 8,525 BTUs |
| 3.5 kW | 3,500 watts | 11,935 BTUs |
| 5.0 kW | 5,000 watts | 17,050 BTUs |
| 7.0 kW | 7,000 watts | 23,870 BTUs |
Suddenly, this becomes a lot clearer:
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A 3.5 kW kit delivers about 12,000 BTUs
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A 5 kW kit delivers about 17,000 BTUs
That’s a 42% jump in heating power.
And when winter hits, trust me — every one of those BTUs matters.
🌬️ 3️⃣ Why Heat Kits Matter More in Winter Climates Than Cooling
Cooling performance depends mostly on:
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Room size
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Sun exposure
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Humidity
Heating performance depends on all of that PLUS:
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outdoor temperature
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wind chill
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insulation
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heat loss
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window leakage
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north-facing exposure
This is why the U.S. Department of Energy warns that heat pumps lose efficiency quickly in cold climates:
🔗 https://www.energy.gov/energysaver/heat-pump-systems
❓Why does this matter?
Because once a heat pump loses power, the heat kit becomes the ONLY thing keeping you warm.
If you size that heat kit wrong, you’ll feel it immediately.
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Room never reaches setpoint
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Overnight temps drop
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PTAC runs constantly
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Electricity bills climb
This is why sizing heating wattage is just as important as cooling BTUs — maybe even more important if you live north of Tennessee.
❄️ 4️⃣ 10 Signs Your Room Needs More Than a 3.5 kW Heat Kit
These are the symptoms I look for when visiting customers in winter:
⚠️ Sign #1: Your PTAC blows warm air but the room stays cold
That means heat loss > heat production.
⚠️ Sign #2: The PTAC runs nonstop on cold days
If it never cycles off, the heat kit is undersized.
⚠️ Sign #3: You wake up colder than when you went to bed
Rooms lose heat to the outdoors overnight — especially bedrooms near exterior walls.
⚠️ Sign #4: It takes more than an hour to warm the room
Undersized heat kits have slow “recovery” times.
⚠️ Sign #5: Your room has drafts or cold floors
Garages, basements, and additions need more wattage.
⚠️ Sign #6: Windows frost or sweat in the winter
Indicates extreme heat loss.
⚠️ Sign #7: You have electric bills that spike in winter
A small heat kit running nonstop costs more than a bigger heat kit running efficiently.
⚠️ Sign #8: North-facing rooms stay coldest
They get no direct sun and lose heat faster.
⚠️ Sign #9: Rooms above garages lose heat 2x faster
Garage ceilings are notorious heat sinks.
⚠️ Sign #10: You live anywhere with real winter
Plain and simple — cold climates need more heating wattage.
If you’ve experienced even 2–3 of these symptoms, stepping up to a 5 kW kit isn’t just worth it — it’s necessary.
🧮 5️⃣ Tony’s Heat Kit Sizing Formula (The Easiest You’ll Ever See)
This is the formula I’ve used for 30+ years.
STEP 1 — Start with room size
Use 20 BTUs per square foot.
STEP 2 — Multiply by the winter climate factor
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Warm climates → × 1.0
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Mixed climates → × 1.2
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Cold climates → × 1.5
STEP 3 — Adjust for real-world heat loss factors
Add:
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+10% for each large window
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+15% for rooms over a garage
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+20% for poor insulation
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+15% for corner rooms
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+25% for basements
STEP 4 — Convert desired BTUs to kW
Use BTUs ÷ 3.41 = watts
STEP 5 — Round up to the nearest available heat kit size
This ensures proper heating without undersizing.
🌡️ 6️⃣ Region-by-Region Heat Kit Recommendations
This is where climate really matters. Referencing EnergyStar’s climate guidance:
🌴 WARM CLIMATES (Florida, Texas Gulf Coast, Louisiana)
✔️ 3.5 kW is typically enough.
✔️ 2.5 kW often works fine for small rooms.
❗ 5 kW only needed for poor insulation or room over garage.
❗ Humidity matters more than heating.
🌤️ MIXED CLIMATES (Carolinas, Tennessee, Virginia, Missouri)
✔️ 3.5 kW is fine for rooms under ~350 sq ft.
✔️ 5 kW recommended for:
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rooms with multiple windows
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rooms over a garage
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rooms with poor insulation
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rooms above 350–400 sq ft
❄️ COLD CLIMATES (Minnesota, Wisconsin, Michigan, New York, New England)
✔️ 5 kW strongly recommended
✔️ 7 kW for large rooms or severe winters
✔️ Heat pump alone won’t cut it
✔️ 3.5 kW will struggle below freezing
✔️ North-facing rooms MUST upgrade wattage
Rooms in Minneapolis can lose as much as 30–50% more heat in January than rooms in warm climates.
🪟 7️⃣ Insulation, Window Count & Room Location: The Hidden Heat Loss Monsters
These factors SLAM heating performance harder than homeowners realize.
Let’s break them down.
❄️ Large Windows = Big Heat Loss
A single large window can add 10–25% heat loss.
❄️ Multiple Windows = Even More Heat Loss
Bedrooms with two or three windows need more wattage.
❄️ North-Facing Rooms Are Cold
No sun = higher heat demand.
❄️ Rooms Over a Garage Lose Heat 2X Faster
Garage ceilings are uninsulated in most homes.
❄️ Corner Rooms Lose Heat on Two Walls
This increases heating load by 15–25%.
❄️ Basement Rooms Stay Cold
Basements bleed heat into the foundation.
If ANY of these apply, stepping up to 5 kW heat kits should be considered mandatory.
🔌 8️⃣ Electrical Requirements: Is a 5 kW Heat Kit Safe to Install?
Yes — as long as your circuit supports it.
Heat kits increase the PTAC’s amperage draw.
Typical PTAC amp draws:
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3.5 kW kit: ~16–18 amps
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5.0 kW kit: ~22–25 amps
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7.0 kW kit: ~28–32 amps
This affects:
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breaker size
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wiring
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receptacle
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plug type
Most 5 kW PTACs need:
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20A or 30A dedicated circuits
Before upgrading, check your electrical panel.
If unsure, consult a pro — a quick 5-minute inspection saves you from tripping breakers all winter long.
🧊 9️⃣ Real-World Case Studies: When Upgrading to 5 kW Saved the Day
Here are real situations where stepping up wattage fixed everything.
🥶 **Case #1 — Minneapolis, MN
320 sq ft Bedroom Over a Garage**
Problem:
3.5 kW heat kit kept room at only 65–68°F on cold nights.
Fix:
Upgraded to 5 kW.
Result:
Room stays at 72°F even in single-digit temperatures.
🪟 **Case #2 — Chicago, IL
North-Facing Apartment with Two Windows**
Problem:
Room felt drafty and heat pump shut down in cold weather.
Fix:
Switched to 5 kW heat kit.
Result:
Room reaches setpoint easily, shorter cycles.
🧊 **Case #3 — Pennsylvania
Guest Room with Poor Insulation**
Problem:
PTAC ran nonstop in winter with 3.5 kW.
Fix:
5 kW upgrade + sleeve insulation kit.
Result:
Cut runtime in half, improved comfort dramatically.
🏨 **Case #4 — Hotel Room, Upstate NY
Used Year-Round with High Occupancy**
Problem:
Frequent complaints of “cold” even at high setpoints.
Fix:
All 3.5 kW units upgraded to 5 kW.
Result:
Boosted guest comfort in winter; no more emergency service calls.
🧠 🔟 Tony’s Quick Choosing Guide
This is the cheat sheet I give customers daily.
✔️ Choose 3.5 kW if:
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You live in a warm climate
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Room is under ~350 sq ft
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Good insulation
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No large windows
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Room is interior or on second floor
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Winters are mild (above 30°F most days)
✔️ Choose 5 kW if:
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You live in a cold winter climate
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Room is over 350 sq ft
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Room has 2+ windows
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Room is over a garage
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Room is north-facing
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Room loses heat quickly at night
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You frequently rely on heating
✔️ Choose 7 kW if:
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Room is large
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Climate hits 0°F often
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You need fast morning recovery
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You want hotel-level heating power
🏁 11️⃣ Tony’s Final Take: Heating Isn’t the Place to Cut Corners
Here’s the truth after 30+ years in the field:
👉 **Cooling problems annoy people.
Heating problems make people miserable.**
When your PTAC is undersized for heating, you feel it instantly:
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cold floors
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drafty walls
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slow warm-ups
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all-night cycling
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uneven comfort
Stepping up from a 3.5 kW heat kit to a 5 kW model is one of the highest-impact upgrades you can make for winter comfort.
It’s not about spending more — it’s about buying the wattage that matches the climate, the room, and the way YOU actually live.
Get the wattage right, and your PTAC becomes a winter powerhouse. Get it wrong, and you’ll be fighting that thermostat all season long.
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In the next topic we will know more about: What Hotels Know About System Sizing That Homeowners Often Miss
