Hey folks, Mike here. If you’re reading this, you’re probably in the middle of figuring out whether a 3.5–4 ton A-Coil (like the Goodman CHPTA4830C3) is right for your system—or maybe you just want to understand what all this “ton” talk means.
I’ll be honest: coil sizing is one of those topics that gets confusing fast. But the good news? Once you understand the basics—what a ton means, how it ties to your home’s square footage, and why matching your coil to your condenser matters—you’ll feel confident making the right choice.
Let’s break this down step by step, no jargon overload.
🌀 1. What Does “3.5–4 Tons” Mean in HVAC?
In HVAC, “tons” don’t refer to weight—they refer to cooling capacity.
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1 ton = 12,000 BTUs (British Thermal Units) per hour.
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So:
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3.5 tons = 42,000 BTUs/hour
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4 tons = 48,000 BTUs/hour
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When you see a coil rated 3.5–4 tons, it means it can pair with outdoor units in that capacity range. Manufacturers design coils with flexibility so they can match a range of condensers without mismatched performance.
👉 Think of it like tires that fit both a midsize SUV and a larger crossover—same part, but it works for both.
📖 Source: Energy.gov – Sizing a Central Air Conditioner
📐 2. Rule of Thumb Sizing: Square Footage vs Tonnage
A common starting point in HVAC is the rule of thumb method:
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1 ton of cooling per 500–600 sq. ft. of living space.
By that rule:
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A 3.5 ton coil suits ~1,750–2,100 sq. ft.
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A 4 ton coil suits ~2,000–2,400 sq. ft.
That’s why you’ll often hear contractors recommend a 3.5–4 ton system for an average midsize home in the U.S.
⚠️ BUT—and this is important—square footage is only a rough guide. Other factors like insulation, windows, and climate can change the right size dramatically.
📖 Source: HVAC.com – How to Size Your Air Conditioner
🏡 3. Beyond Square Footage: The Real Factors
If there’s one thing I’ve learned, it’s that two houses with the same square footage can need completely different cooling power. Why?
Here are the biggest factors beyond size:
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Climate Zone 🌡️
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A 2,000 sq. ft. home in Minnesota might get by with 3 tons.
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The same home in Florida probably needs 4 tons or more.
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Insulation & Air Sealing 🧱
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Tight modern homes need less cooling.
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Drafty older homes bleed air and need more.
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Windows & Orientation 🪟
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South- or west-facing homes gain more heat.
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Large unshaded windows = higher cooling loads.
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Ceiling Height & Layout 🏠
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Open floor plans and vaulted ceilings increase volume.
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A chopped-up home with lots of small rooms may need less.
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👉 That’s why square footage alone is never enough.
📖 Source: ACCA – Manual J Residential Load Calculation
🔗 4. Why Coil & System Matching Matters
The coil doesn’t work in isolation—it’s part of the whole system.
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Match to the outdoor condenser tonnage.
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A 3.5 ton condenser needs a 3.5 ton coil.
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A 4 ton condenser needs a 4 ton coil.
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Match to the blower/furnace capacity.
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If your blower can’t push enough air across the coil, the system won’t cool properly.
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TXV (thermal expansion valve).
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Coils like the Goodman CHPTA4830C3 come with a built-in TXV, which regulates refrigerant flow to match the condenser. This makes matching easier and more efficient.
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If you mismatch—say, a 3 ton coil with a 4 ton condenser—you’ll get poor efficiency, higher bills, and possible system failure.
📖 Source: Goodman – CHPTA Coil Specs
⚖️ 5. Undersizing vs. Oversizing: Both Are Bad
When it comes to coils and systems, “bigger is better” is a myth.
❌ Undersized Coil/System
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Runs constantly to keep up.
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Never quite cools the home.
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Poor dehumidification—leaves air sticky.
❌ Oversized Coil/System
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Cools too fast, causing short cycling.
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Higher indoor humidity (no time to dehumidify).
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Uneven temperatures and wasted energy.
👉 I once saw a neighbor install a 5 ton system in a 2,000 sq. ft. home. Sure, the air got cold fast—but the house felt clammy, and their bills went up.
📖 Source: Energy Vanguard – The Problems with Oversized ACs
📊 6. When a 3.5–4 Ton Coil Hits the Sweet Spot
Here’s when I’d say a 3.5–4 ton coil is usually the right choice:
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Homes 1,800–2,400 sq. ft. in average U.S. climates.
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Two-story homes with moderate insulation.
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Homes with 3–5 occupants and standard appliance loads.
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Replacements for existing 3.5–4 ton systems where performance was acceptable.
Mike’s Rule: “If your home is midsized and you live in an average climate, chances are a 3.5–4 ton coil is your Goldilocks size—not too small, not too big.”
🧮 7. The Gold Standard: Manual J Load Calculation
At the end of the day, the only way to know for sure is a Manual J load calculation.
What it considers:
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Square footage
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Climate zone
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Insulation levels
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Window type and placement
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Air infiltration rates
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Occupancy and appliance loads
Contractors use software to crunch all these numbers. It’s the most accurate way to determine if you need 3.5, 4, or another size.
Yes, it costs a little, but it can save thousands in mistakes.
📖 Source: U.S. Department of Energy – AC Sizing
💡 8. Mike’s Takeaway Tips
Here’s my cheat sheet after years of installs and mistakes:
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✅ Always match coil size to condenser size.
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✅ Use square footage as a starting point, not the final word.
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✅ If in doubt, pay for a Manual J—it’s worth it.
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✅ Don’t let a contractor upsell you on “bigger.” Bigger often means worse comfort.
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✅ A 3.5–4 ton coil is ideal for many midsize homes, but every home is unique.
My bottom line: “Sizing your coil right means comfort, efficiency, and fewer headaches down the road.”
In the next topic we will know more about: Single-Stage vs. Two-Stage Systems: Which Works Best with This Coil?
