❄️ Is a 3 Ton Horizontal AC the Right Size for Your Home? Mike’s Sizing Guide
🧰 Introduction — Why Sizing Matters (and Why Mike Cares)
Hi, I’m Mike. If there’s one lesson I’ve learned after years of fiddling with HVAC systems, it’s this: comfort doesn’t come from buying the biggest AC you can afford. It comes from buying the right size.
The problem? Most homeowners either:
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Guess based on house size (“my neighbour has 3 tons, so I probably need 3 tons too”), or
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Oversized out of fear (“bigger must be better, right?”).
Both lead to problems: an undersized system runs constantly and never cools; an oversized one cycles too quickly, wastes electricity, and leaves your house sticky with humidity.
In this guide, I’ll answer the big question:
👉 Is a 3-ton horizontal AC the right size for your home?
We’ll dig into:
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What “3 tons” really means
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How to estimate cooling needs properly (step-by-step)
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Why horizontal units have special quirks
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Real-world stories from my own installation
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Pitfalls that trip people up
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A clear checklist so you can decide
By the end, you’ll know whether a 3-ton horizontal system (like the Goodman GPCH33631) is your match — or if you should size up, size down, or rethink.
📏 1. The Basics: Tonnage, BTUs, and Square Footage
🧊 1.1 What does “3 ton” mean in AC terms?
In HVAC, “tons” measure cooling capacity, not weight. One ton = 12,000 BTU/hr. So:
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1 ton = 12,000 BTU/hr
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2 ton = 24,000 BTU/hr
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3 ton = 36,000 BTU/hr
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4 ton = 48,000 BTU/hr
That means a 3-ton system can remove about 36,000 units of heat from your home every hour.
📐 1.2 The square footage rule of thumb
A quick-and-dirty sizing method: 1 ton per 450–600 ft² of space.
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2 ton → ~900–1,200 ft²
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3 ton → ~1,350–1,800 ft²
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4 ton → ~1,800–2,400 ft²
Resources like LearnMetrics and Carney & Son confirm this.
But remember — this is only a starting point.
⚠️ 1.3 Why rules of thumb fail in real life
That neat rule assumes:
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8 ft ceilings
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Average insulation
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Average window sizes and shading
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Moderate climate
If your home differs (high ceilings, tons of west-facing glass, bad insulation, humid summers, etc.), the math changes. That’s why pros use Manual J load calculations — more accurate but harder for homeowners to DIY.
For homeowners like us, online calculators can refine things:
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Remodelling Calculator’s AC size tool factors in climate zones and insulation.
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A2Z AC tonnage calculator gives quick BTU estimates.
🏠 2. Horizontal vs. Vertical AC: Why Orientation Matters
🔄 2.1 What’s a horizontal unit?
A horizontal air conditioner has airflow parallel to the ground. It’s typically tucked into attics, crawlspaces, or tight utility areas.
A vertical unit stands upright in basements or closets.
🔧 2.2 Pros & cons of horizontal systems
Pros:
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Fits where vertical units won’t (attics, low-clearance rooms)
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Easier duct branching sideways.
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Often quieter inside living areas.
Cons:
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Can suffer duct losses if the attic gets too hot
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Drainage is trickier (condensate must slope correctly)
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Service access is sometimes harder.
More on this in The Furnace Outlet’s guide to horizontal vs. vertical ACs.
📊 2.3 Does orientation change sizing?
Not directly — 3 tons of capacity is 3 tons, regardless of orientation.
But in practice, horizontal systems in hot attics or tight crawlspaces lose efficiency. That means:
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If your load calc says 2.8 tons, you might want to round up to 3.
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If ducts are leaky or long, capacity loss may push you higher.
Larson Air notes these real-world installation losses are a key reason people sometimes oversize.
🧮 3. Step-by-Step: How I (Mike) Size a 3 Ton Candidate
Let’s walk through my DIY-friendly method.
3.1 Step 1: Measure area & volume
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Conditioned area (ft²)
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Ceiling height (ft)
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Volume = area × ceiling height
Example:
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1,600 ft² home × 9 ft ceilings = 14,400 ft³ volume
3.2 Step 2: Baseline BTU estimate
Formula: BTU = area × 20–25
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Low: 1,600 × 20 = 32,000
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High: 1,600 × 25 = 40,000
That’s ~2.7 to 3.3 tons.
3.3 Step 3: Adjust for real factors
| Factor | Effect | My adjustment |
|---|---|---|
| Poor insulation | Add 10–15% | Old house = +10% |
| Big west windows | Add 8–10% | My house = +8% |
| Shading | Subtract 5% | Trees helped = –5% |
| Duct losses | Add 5–10% | Long attic runs = +6% |
| Occupants & appliances | Add 500–1,000 BTU per person over 2 | Family of 4 = +1,500 |
So my adjusted range grew to ~38,000–47,500 BTU (3.2–4 tons).
3.4 Step 4: Sanity check with calculators
When I plugged numbers into the Remodelling Calculator, it also suggested ~3.2–3.5 tons for my area. That reassured me that my hand math wasn’t crazy.
3.5 Step 5: Make the decision
I went with 3 tons anyway — because:
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I improved duct insulation.
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My attic got ventilation upgrades.
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I preferred slightly undersized (longer runs, better dehumidification)
And it worked — though on very hot days, it runs nearly full-tilt.
🎯 4. When 3 Ton Fits vs. When It Doesn’t
✅ 3 Ton is a good fit if:
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Home is 1,300–1,800 ft²
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8–9 ft ceilings
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Good insulation
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Moderate climate
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Reasonable window area/shading
⚠️ 3 Ton may be too small if:
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Home >1,800 ft²
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Lots of sun-facing glass
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Poor insulation / leaky ductwork
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Hot, humid climate
🚫 3 Ton may be oversized if:
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Home <1,300 ft²
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Tight, well-insulated shell
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Mild climate
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Low ceilings
🛠️ 5. My Real-World Story with a Horizontal 3 Ton
When I installed my Goodman 3-ton horizontal system:
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The good: It cooled well, dehumidified better than expected, and fit in my attic where a vertical never could.
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The challenge: On 98°F summer days, it ran almost nonstop.
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The fix: I upgraded attic insulation and added shading film on west windows. That made the 3-ton feel “just right.”
Lesson: Installation details matter as much as tonnage.
🔍 6. Common Sizing Mistakes
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Bigger = better thinking → causes short cycling & clammy air.
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Ignoring duct losses → a 3-ton unit might only deliver 2.5 tons if ducts leak.
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Not factoring in attic heat → horizontal units in hot attics need extra buffer.
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Forgetting future changes → adding an extension? Plan.
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Skipping clearance → tight installs make service a nightmare.
✅ 7. Mike’s Quick Sizing Checklist
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Home size in 1,300–1,800 ft²?
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Baseline BTU 32,000–40,000?
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Adjusted for insulation, windows, duct losses?
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Horizontal orientation challenges considered?
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Future changes accounted for?
If yes → 3 ton is likely your match.
🏁 Conclusion — Is 3 Ton Right for You?
If your home is in that 1,300–1,800 ft² range, and you’ve accounted for insulation, ductwork, and climate, then 3 tons is usually the sweet spot — especially in a horizontal design.
But don’t skip the details: a poorly installed 3-ton can underperform, while a carefully installed one can outperform a sloppy 4-ton.
My advice? Run the numbers, check the adjustments, and don’t oversize just for peace of mind. That’s what I did — and it’s kept my home comfortable without spiking my electric bill.
In the next blog, we shall learn more about R-32 vs. R-410A: Why Mike Chose the R-32 Goodman AC in 2025
