Hey folks, Tony Marino here. If you’re shopping for a new PTAC unit, you’ve probably run into this little acronym: BTU. You know it matters. You know too many or too few can mess things up. But how do you actually figure out what size you need?
Let’s cut through the noise and talk about real-world PTAC sizing. No fluff. No formulas you need a degree to understand. Just what you need to know to cool (and heat) your space the right way.
What the Heck Is a BTU?
BTU stands for British Thermal Unit—basically, it’s the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit.
When it comes to PTACs, think of BTUs as horsepower for your comfort. The more BTUs, the more power your unit has to cool or heat a room. But too much isn’t better—it’s inefficient, loud, and more expensive upfront.
General Rule of Thumb: BTU vs Square Footage
Here's a straight-up size chart you can actually use:
| Room Size (sq ft) | Recommended BTUs |
|---|---|
| Up to 300 | 7,000–9,000 BTUs |
| 300–400 | 9,000–12,000 BTUs |
| 400–500 | 12,000–15,000 BTUs |
| 500–700 | 15,000–17,000 BTUs |
| 700–1,000 | 17,000–24,000 BTUs |
Now hold up—this isn’t the whole story.
Factors That Change Your BTU Needs
Not all square footage is created equal. Here are a few things that can throw those numbers off:
1. Climate
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Hot, humid areas like Florida or Texas? Bump up your BTUs by 10%.
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Mild zones? You’re probably good sticking to the base numbers.
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Cold climates? If you're relying on PTAC for heat too, go higher.
2. Insulation
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Poor insulation or older buildings? Add 10–15% more BTUs.
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Well-insulated rooms with energy-efficient windows? You might be able to go on the low end.
3. Sun Exposure
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South- or west-facing rooms with big windows? Add 10%.
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Shaded or basement rooms? You can size down a little.
4. Ceiling Height
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The chart above assumes 8-foot ceilings. If you’ve got vaulted ceilings, consider upgrading BTUs accordingly.
What Happens If You Oversize or Undersize?
Let me be real with you:
Too Small =
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PTAC runs constantly
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Can’t cool or heat effectively
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Wears out faster
Too Big =
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Cools too quickly, doesn’t remove humidity
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Short cycling = more wear & tear
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Higher upfront and operating costs
Bottom line: Right size = right comfort, right efficiency.
Common PTAC Sizes You’ll See
Most PTAC units fall in the 7,000 to 15,000 BTU range. Here’s what each is typically used for:
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7,000–9,000 BTUs: Smaller hotel rooms, offices, dorms
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9,000–12,000 BTUs: Average residential bedrooms or studios
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12,000–15,000 BTUs: Suites, open-plan apartments, larger rooms
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15,000+ BTUs: Oversized rooms, small commercial spaces
Need heat too? Most models come with electric heat or heat pump backup, so be sure to factor that into your decision if you're buying for year-round use.
Tony’s Sizing Tips Before You Buy
✅ Measure your room—length × width = square footage
✅ Think about how many people use the space regularly
✅ Don’t forget sun exposure, windows, and insulation
✅ If in doubt, ask a pro or reach out to us—better to size it right than guess wrong
Wrap-Up from Tony
Getting your BTUs right isn’t rocket science—but it does matter. Go too small and you're sweating. Go too big and you’re throwing money away.
If you’re ready to shop, head over to The Furnace Outlet's PTAC Collection. You’ll find R-32 units in all the right sizes, and I’ll be here to walk you through it if you’ve got questions.
