Meet Alex, the Sweaty Homeowner Wondering “Why Is My AC Always Running?”
Alex bought a charming 1,400 sq ft. starter home in July. By noon, the living room feels like a greenhouse, and the air conditioner never seems to catch up. He’s worried about his power bill—and his sanity. Sound familiar? Many homeowners overshoot or undershoot their cooling load because BTU numbers look like code on a spaceship console. In this guide, we translate those numbers into clear steps you can follow today. We’ll tap our 20-year wholesale experience at The Furnace Outlet to show you how to size, save, and chill out without pricey guesswork or “just-trust-me” upsells.
What Exactly Is a BTU, and Why Should You Care?
A British Thermal Unit (BTU) is the heat needed to raise one pound of water by one degree Fahrenheit. Think of it as a calories-for-comfort score. More BTUs mean more cooling muscle. For homes, you’ll usually see BTUs per hour. Understanding the number behind the label helps you dodge oversized units that short-cycle and under-sized units that wheeze all summer. Energy.gov offers a handy primer on the science if you like deeper dives.
[Energy Saver] (https://www.energy.gov/energysaver/central-air-conditioning). But stay here, we’ll keep it simple and actionable.
Rule of Thumb: From Square Footage to BTU in Two Steps
Grab your tape measure, find your home’s square footage, and multiply by 20–25. A 1,000 sq ft. space lands near 20,000–25,000 BTUs. Divide that by 12,000 to convert to tons (about 1.5–2 tons). It’s not magic, just math. Need a free calculator? Swing by our Help Center for a plug-and-play worksheet created by our licensed techs.
Beyond Square Footage: Windows, People, and Sunlight Add Heat
Square footage is the start, not the finish. Add roughly 200 BTU per person and 200 BTU per window. Bump BTUs up 10 % for sun-flooded rooms; shave a bit off for deep shade. Tall ceilings above eight feet? Increase capacity by the same percentage as the extra height ratio. EnergyStar’s guide (https://www.energystar.gov/products/heating_cooling/air_conditioning_room#tab-how_to_choose) backs these tweaks and keeps your numbers grounded in real physics.
From BTU to Tons: Converting Numbers Into Everyday Language
Manufacturers often rate central ACs in tons, not BTUs. Remember: 1 ton = 12,000 BTU/h. So the 30,000 BTU load for Alex’s growing family equals 2.5 tons. Once you nail the tonnage, browse our R-32 heat pump systems or R-32 AC and coils to match capacity with cutting-edge refrigerant tech. For the engineering backstory, Building
Oversized vs. Undersized Units: Real Costs Hidden in Plain Sight
Bigger isn’t better. An oversized system cools the air fast but can’t de-humidify, causing that “cold-and-clammy” cave feeling while spiking start-up electricity. Undersized units run non-stop, torching your utility bill and your patience. Consumer Reports tracks these cost swings in real-world tests. Need accessories like smart thermostats to sharpen control? Browse our HVAC accessories for easy add-ons.
Manual J Load Calculations: When You Need Pro-Level Precision
Rules of thumb are great for quick checks, but life gets messy—insulation gaps, leaky ducts, odd sun angles. A Manual J calculation crunches these variables with software and training. Our Design Center offers free load-calc help over chat or phone with an on-staff HVAC engineer. Want to DIY the math? The Air Conditioning Contractors of America (ACCA) hosts the Manual J standards you can study (https://www.acca.org/hvac/technical/manuals). Either way, treat Manual J as your sizing gold standard when comfort has to be perfect.
Real-World Sizing Table: Match Your Home to the Right AC
|
Home Size (sq ft.) |
Approx. BTUs |
Tons |
|
700–1,000 |
18,000 |
1.5 |
|
1,000–1,200 |
21,000 |
1.75 |
|
1,400–1,600 |
24,000 |
2 |
|
1,800–2,000 |
30,000 |
2.5 |
Pair the numbers with our package units or through-the-wall ACs when space or budget drives the decision. Remember, the table assumes average insulation and 8-foot ceilings, adjust up or down per Sections 4 and 7.
DIY Sizing Checklist: Grab a Tape Measure, Not a Guess
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Measure each room and total the square footage.
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Count windows, occupants, and note sun exposure.
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Multiply by 20–25 BTU, then add extras from Step 2.
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Divide by 12,000 to get tons.
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Cross-check with the table above.
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Still unsure? Contact our licensed HVAC techs for free advice, no pressure.
Want an easy-install option? Our DIY mini-split kits come pre-charged and include step-by-step videos.
Budget-Friendly Fixes Before You Replace the Whole System
New equipment isn’t always Step 1. Tighten ducts, add attic insulation, or install reflective window film; each can shave BTU demand and let your existing unit breathe. Explore affordable parts in our accessories aisle or drop your question in the live chat an actual tech, not a bot, will guide you. Honest advice first, new gear second: that’s our pledge and backed by a satisfaction guarantee.
Next Steps: Free Design Help and Wholesale Savings Await
Ready to size with confidence? Use the checklist, then call, chat, or email our team. We’ll double-check your numbers, recommend parts, and ship fast, often the same day. Plus, our lowest price guarantee means you never pay retail markup. Whether you pick a room AC or a full commercial package unit, you get warehouse pricing and a human on the phone when questions pop up. That’s the Furnace Outlet way: straight talk, solid gear, and cool comfort year after year.
