Choosing the Right PTAC Size for Your Space (BTU & Square Footage Guide)

🛠️ Why PTAC Sizing Matters—A Word from Tony

Let me tell you something from experience: the most common mistake I see when it comes to PTAC installations? People pick the wrong size. Either they go too small to save a few bucks, or they go too big thinking it’ll cool faster.

Wrong both times.

An undersized PTAC will run constantly, waste energy, and still leave you sweating. An oversized one? It’ll short-cycle, wear out faster, and won’t properly dehumidify the room, leaving the space clammy.

This guide is here to help you avoid those headaches by giving you a step-by-step system for choosing the right PTAC size—measured in BTUs (British Thermal Units)—based on your room’s square footage, layout, climate, insulation, and more.

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📏 Understanding BTUs: What They Are and Why They Matter

A BTU is a measure of how much heat a unit can add or remove in an hour.

• The higher the BTU rating, the more powerful the unit.

• But more isn't always better. If your BTU output is too high for the room, you’ll end up with wasted energy and uneven comfort.

Most PTAC units fall between 7,000 and 15,000 BTUs, and your job is to match that number to your actual heating and cooling needs.

According to Energy Star, the starting point is square footage—but that’s just the beginning.

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📐 Step 1: Measure Your Room’s Square Footage

The first thing you need to do is get the exact square footage of the room you want to condition. This isn’t the time to eyeball it—grab a tape measure and do it right.

Formula:

So if your room is 18 feet long by 12 feet wide:

For oddly shaped rooms, break it up into rectangles and add the total.

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🔢 Step 2: Use the General Sizing Chart (Baseline BTU Guidelines)

Here's the basic BTU sizing chart used by HVAC pros for a single room with standard ceiling height (8 ft), average insulation, and normal sun exposure.

So, for a 400 square foot room, you’re looking at a 10,000–12,000 BTU PTAC.

But remember: this is just your starting point.

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🔄 Step 3: Adjust for Room Conditions

Once you’ve got the base BTU from square footage, it’s time to adjust for real-world conditions. Let’s break these down.

☀️ 1. Sunlight Exposure

If your room gets direct sun most of the day (think west-facing windows), add 10% more BTUs to compensate.

• Example: 10,000 BTU base × 1.10 = 11,000 BTUs needed.

🏘️ 2. Room Insulation

Older buildings or rooms with poor insulation lose heat faster in winter and gain it in summer.

• Poor insulation: Add 10–20% more BTUs.

• Newer, energy-efficient builds: Stick to the base.

Check out this DOE resource on insulation standards to see how your space stacks up.

🍳 3. Kitchens or Rooms with Appliances

Kitchens generate a ton of heat from ovens, fridges, dishwashers, etc.

• If you’re installing in a kitchen or appliance-heavy room, add 4,000 BTUs to your total.

👥 4. High Occupancy

Every person in a room gives off heat. If the space is normally occupied by more than two people, add 600 BTUs per extra person.

• A classroom or group housing room for 4 people? That’s an extra 1,200 BTUs.

🌡️ 5. Climate Zone

Where you live matters—a lot. Hotter zones need more cooling power.

Here’s a rough map of climate zones:

• Zones 1–2 (South/Southwest): Add 10% to your BTU count.

• Zones 3–4 (Midwest/East Coast): No adjustment.

• Zones 5–7 (North, Northwest): If you’re sizing for heat, you may want a unit with electric heat backup in colder months.

You can view your climate zone on the U.S. Building America Climate Zone Map.

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📋 Example: Sizing a PTAC for a Real Room

Let’s say you’re installing a PTAC heat pump in a studio apartment that’s:

• 400 sq ft

• West-facing with lots of windows ☀️

• Two people living there 👨👩

• In Dallas, TX (Hot Climate Zone) 🌵

• Good insulation

• Has a small kitchen 👩🍳

Here’s how we do it:

• Base BTUs: 10,000

• Sunlight adjustment: +1,000 (10%)

• Kitchen adjustment: +4,000

• Occupancy: No extra needed

• Climate: +1,000 (10%)

Total: 10,000 + 1,000 + 4,000 + 1,000 = 16,000 BTUs

👉 A 15,000–17,000 BTU PTAC heat pump would be ideal here. Even though the square footage is 400, the kitchen and climate really pushed it up.

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🧊 But Wait—Heating & Cooling Are NOT Equal

Here’s a curveball: A lot of PTAC units have separate BTU ratings for heating and cooling.

So your unit might say:

• 12,000 BTU Cooling

• 11,000 BTU Heat Pump

• 13,000 BTU Electric Heat

Make sure both numbers line up with your climate’s demands. In colder areas, the heat pump alone may not cut it, and you’ll want electric resistance backup heating built-in.

For more on heat pump performance in winter, check Consumer Reports’ guide on heat pump heating capacity.

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🔌 Voltage Considerations (Don’t Skip This Part)

Most residential PTACs run on either:

• 208/230V – standard for most buildings

• 265V – used in some commercial or older buildings

👉 Always check your existing wiring or have a licensed electrician do it. Ordering the wrong voltage is an expensive mistake.

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🛒 Best-Selling Sizes on the Market

At The Furnace Outlet, the most popular PTAC sizes people go for are:

• 9,000 BTU – For small rooms, hotel-style setups

• 12,000 BTU – Medium rooms, offices, home add-ons

• 15,000 BTU – Large rooms, studios, open-plan spaces

These models are available in both R-32 refrigerant systems and classic R-410A (though R-32 is taking over due to higher efficiency and lower GWP).

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🧰 Tips for Getting the Most from Your PTAC

Once you’ve chosen the right size, don’t stop there—get better performance with these pro tips:

✅ Seal and Insulate Around the Wall Sleeve

Air leakage around the chassis wastes BTUs. Use foam gasket kits and weatherstripping.

✅ Clean the Filter Monthly

A clogged filter reduces airflow and strains the compressor.

✅ Upgrade to a Wall Thermostat

This allows for more accurate temperature readings and scheduled operation.

✅ Keep the Drainage System Clear

Condensate backups can damage your unit and lead to water leaks.

✅ Don’t Oversize

I’ll say it again—bigger isn’t better. If your unit keeps shutting on and off every few minutes, you’ve overshot the BTUs and you’ll wear the system down faster.

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🧠 Final Thoughts from Tony

Buying a PTAC isn’t complicated if you go into it with the right info. Get your square footage, climate, and room conditions right, and you’ll have a system that runs smooth for years.

The wrong BTU size can ruin comfort, waste energy, and cost you way more in the long run than just doing it right the first time.

So if you're shopping for a PTAC, start by matching your BTU rating to your space, then take a look at The Furnace Outlet’s PTAC collection for high-efficiency models that deliver cooling and heating year-round.

And if you’re still not sure which one fits your space, just holler. I’ll help you figure it out—no fluff, no upsell, just the right size for your job.