Real Job Breakdown — How Mike Sized a Goodman 80k for a 1,600 Sq. Ft. Home

🎯 1️⃣ Why This Job Matters

“Sizing isn’t about guessing — it’s about knowing. Every furnace I install starts with math, not muscle.”

When people ask me how I “pick the right furnace,” they expect some secret number or rule-of-thumb shortcut. Truth is, there’s no magic — just good math, ductwork knowledge, and a lot of experience sweating in attics.

This particular job in Columbus, Ohio became a textbook example of how to size a system properly. The homeowner called about replacing an aging 90,000 BTU unit. Most contractors would’ve said, “Let’s just match what you had.” But that’s how you end up with oversized systems that waste energy.

I wanted to show that a perfectly sized system performs better, costs less, and lasts longer — and the Goodman 96 AFUE 80,000 BTU model turned out to be the hero of the story.

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🏠 2️⃣ The Home: Specs, Condition & First Impressions

The house sat in a quiet suburb, built right before energy codes got stricter. The insulation was decent but not top-tier. Ducts were intact but showing age — a few leaky joints and one crushed flex connector. Nothing major, but enough to matter in a load calc.

Tony’s Thought: “This house wasn’t a dump — but it wasn’t airtight either. Perfect candidate for a precision-sized system.”

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📏 3️⃣ Step One — The Manual J Load Calculation

Before I even touched the old furnace, I ran a Manual J calculation using ACCA-approved software. This isn’t guesswork — it’s science.

Key Inputs:

• Outdoor design temp: 10°F

• Indoor setpoint: 70°F

• ΔT = 60°F

• Wall R-value: 19

• Attic R-value: 38

• Infiltration: Medium

• Duct loss estimate: 10%

Output:

• Heating Load: 46,200 BTU/hour

• Cooling Load: 30,100 BTU/hour

That 46,200 BTU figure became my North Star. It tells me the home loses about that much heat per hour on the coldest design day.

Now, I never size to match that exact number — you need a small cushion for extreme weather and duct losses. But a cushion, not a couch.

Tony’s Rule: “Give yourself 25–30% margin, not 100%. Bigger isn’t safer — it’s wasteful.”

Reference: ACCA Manual J Overview.

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🧮 4️⃣ Step Two — Matching the Right Goodman Furnace

With the load calculated, I compared model specs. Here’s what I found:

You can see why the Goodman 96 AFUE 80,000 BTU model GR9S960803BN was the ideal fit. It delivers about 76,800 usable BTUs, covering the 46,200 load with room to breathe during deep winter.

Tony’s Quote: “If the load calc says 46k, I don’t go grabbing a 100k. I match the math — not my ego.”

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💨 5️⃣ Step Three — Checking the Ductwork

The ducts are the arteries of your HVAC system. You can have the perfect furnace, but if your airflow’s a mess, the comfort will be too.

I inspected the main trunk lines and ran a static pressure test.

• Target static pressure: 0.5 in WC

• Measured: 0.54 in WC before sealing

• After sealing leaks: 0.49 in WC

Spot-on.

I found a few weak mastic seals near the plenum, plus one undersized return line. I added a 6-inch return branch to balance airflow between the front and back of the house.

That 30-minute duct tune-up improved airflow by 10–12% based on CFM readings.

Reference: Energy Star Duct Sealing Guide.

Tony’s Line: “It’s not always about buying new — sometimes you just need to seal what’s already paid for.”

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🧰 6️⃣ Step Four — Installation & Setup

The New System:

• Furnace: Goodman 96 AFUE 80,000 BTU

• Blower Motor: 9-speed ECM

• Orientation: Upflow in basement

• Duct Transitions: Custom-fit sheet metal

• Thermostat: Smart programmable, Wi-Fi enabled

I also cleaned the condensate drain, flushed the PVC vent, and pressure-tested the gas line for safety.

Once installed, I calibrated the blower speeds:

• Heat mode: 1,100 CFM

• Cool mode: 1,200 CFM

Then ran a full combustion test — flue gas readings came back clean, efficiency right on spec.

Tony’s Note: “Goodman’s 96 AFUEs are predictable — tight seals, smart board, quiet burner start-up. You can feel the quality.”

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🔥 7️⃣ Step Five — Testing & Performance Verification

After installation, I ran a full system test over 24 hours to verify performance in real weather (outdoor temps hovered between 12–18°F).

Readings:

• Supply air temp: 118°F

• Return air temp: 70°F

• ΔT (temperature rise): 48°F (target: 35–55°F)

• Run time per cycle: 12–13 minutes

• Room temperature swing: <2°F

Everything lined up perfectly. The system ran steady and efficient — no short cycling, no cold corners.

Tony’s Takeaway: “Steady heat beats fast heat every time. It’s not about how loud it roars — it’s about how smooth it runs.”

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💡 8️⃣ Step Six — Energy Efficiency & Bill Impact

Before replacement, the old furnace was a 90k BTU, 80 AFUE single-stage unit from 2002. It worked but burned through gas like a pickup idling all night.

Let’s compare:

That’s roughly 24% savings during the heating season — around $400–$450 per year.

Reference: Energy.gov Furnace Efficiency.

Tony’s Quote: “A few BTUs saved per hour doesn’t sound exciting — until your gas bill drops and you realize comfort doesn’t have to cost more.”

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🧊 9️⃣ Step Seven — The Cold Test

To prove the sizing held up, I revisited the home during a January cold snap (7°F outside). The Goodman 80k ran longer cycles but still maintained a steady 70°F indoors, with no comfort dips.

• Longest continuous runtime: 17 minutes

• No cycling alarms or high-limit trips

• Even temperature from front to back: within 1.5°F

The homeowner said:

“For the first time, the back bedrooms actually feel the same as the living room.”

Music to my ears.

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🧠 10️⃣ What I Learned (and You Should Too)

1. Manual J isn’t optional.

Every successful job starts with data. Skip it, and you’re just guessing.

2. Airflow fixes are free efficiency.

The best BTU is the one that actually makes it to your vents.

3. AFUE is only half the story.

You can’t hit 96% efficiency with 70% ductwork performance — the math won’t allow it.

4. Smart controls stretch your BTUs.

The programmable thermostat saved 10% more by smoothing out start-stop cycles.

Tony’s Quote: “I didn’t just install a furnace — I tuned a system. There’s a difference.”

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📉 11️⃣ Before vs. After Snapshot

That last line is key: a steady burn means fewer starts, less wear, and higher comfort consistency.

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🔧 12️⃣ Quick Math: Delivered Efficiency

$$\text{Delivered Efficiency} = \text{AFUE} \times \text{Duct Efficiency}$$

So, 96% × 90% = 86% delivered efficiency.
Compare that to the old setup: 80% × 75% = 60%.

That’s a 43% real-world gain — no exaggeration.

Tony’s Take: “It’s not about paper ratings. It’s about what actually hits your living room.”

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🧾 13️⃣ Homeowner ROI & Payback

But the real payoff? Comfort.
The homeowners immediately noticed quieter operation, smoother warmth, and zero “cold room” complaints — all for the same monthly budget.

Reference: Energy.gov – Cost & Payback for High-Efficiency Equipment.

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💬 14️⃣ Tony’s Advice to Homeowners

If you’re planning a furnace upgrade, here’s what I tell every customer:

1. Don’t size by square footage alone. Climate, insulation, and layout matter more.

2. Always inspect your ducts. Leaks are like leaving a window open in winter.

3. Aim for steady heat, not short bursts. It’s quieter, cheaper, and more comfortable.

4. Invest in efficiency where it counts. Goodman’s 96 AFUE gives real-world results without breaking the bank.

Tony’s Quote: “Heating right isn’t about brute force — it’s about balance.”

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🏁 15️⃣ The Final Results

I couldn’t have asked for a better outcome.

Tony’s Sign-Off:
“You don’t need a bigger furnace — you need a smarter one, installed right.”

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🖼️ Hero Visual Concept

A dynamic, split-scene visual:

• Left: Tony kneeling beside a Goodman 80k furnace with clipboard, pointing to a duct airflow diagram.

• Right: A transparent cutaway of the 1,600 sq. ft. home showing labeled zones (living room, bedroom, kitchen) with red arrows indicating airflow and temperature uniformity.
  Overlay text: “Manual J + Goodman = Comfort That Adds Up.”
  Colors: Goodman red, gray, and white for professional contrast.

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Final Word from Tony:

“Sizing isn’t a guessing game — it’s precision work. The Goodman 80k hit the mark because the math backed it. Every time I run a Manual J, I’m not just selling a furnace — I’m guaranteeing comfort.”

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In the next topic we will know more about: When to Recalculate — Renovations, Additions & the Sizing Reset Button