🌬️ Installation Guide: What Mike Learned Installing His Gas Furnace
🔥 Introduction: From Old Heat to Smart Efficiency
When Ohio homeowner Mike Sanders first bought his house in 2006, it came with a builder-grade 80% AFUE gas furnace — loud, basic, but dependable.
For nearly two decades, it kept his family warm through Midwest winters. But in early December, the system failed — and the repair quote was nearly half the cost of a new furnace.
“The tech told me, ‘You’ve gotten your money’s worth.’ But I wanted more than just another replacement. I wanted to know how it all worked.”
So Mike began researching high-efficiency gas furnaces — the kind that boast 95–97% AFUE ratings and whisper-quiet variable-speed motors. After comparing models at The Furnace Outlet, he landed on a Goodman GMVC96 96% AFUE two-stage furnace.
Instead of leaving it all to the professionals, Mike decided to assist with the installation himself, guided by local codes and professional supervision. His goal: learn exactly what makes modern furnaces so efficient — and see firsthand why installation quality makes or breaks performance.
This is his story — and your step-by-step homeowner’s roadmap to a successful gas furnace installation, from preparation to startup.
🧰 1️⃣ Before You Begin: Planning, Codes, and Preparation
The biggest mistake homeowners make? Thinking furnace installation starts when the box arrives. In truth, half the job happens before you even uncrate the unit.
🧾 Step 1: Confirm the Furnace Type and Orientation
Every furnace has an airflow direction, and installing the wrong orientation can lead to airflow imbalance or condensate pooling.
| Configuration | Description | Typical Location |
|---|---|---|
| Upflow | Air exits through the top | Basements, closets |
| Downflow | Air exits through the bottom | Attics, mobile homes |
| Horizontal | Air moves sideways | Crawlspaces, tight areas |
Mike’s old furnace was an upflow model, with ducts above it feeding the rest of the house. His Goodman GMVC96 matched perfectly, simplifying setup.
📏 Step 2: Sizing the Furnace (BTUs per Square Foot)
Proper sizing ensures both comfort and longevity. Too big, and it cycles on/off constantly; too small, and it runs endlessly.
Mike used the rule of thumb:
35–60 BTUs per square foot, depending on insulation and climate.
For his 2,000 sq. ft. Ohio home:
2,000 × 40 BTU = 80,000 BTU furnace — right in the sweet spot for his region.
📘 Reference: Energy.gov – Furnace Sizing and Efficiency
🧯 Step 3: Safety, Permits, and Tools
Gas appliances require compliance with local mechanical codes (often based on the International Residential Code or NFPA 54).
Mike applied for a mechanical permit ($85) from his city, which covered venting and combustion inspections. He also made sure he had the right tools:
| Category | Essential Tools |
|---|---|
| Plumbing | Adjustable wrench, pipe thread compound |
| Electrical | Wire strippers, multimeter |
| HVAC | Manometer, combustion analyser, PVC cutter |
| Safety | CO detector, gloves, safety glasses |
📗 Reference: NFPA 54 – National Fuel Gas Code
🧱 2️⃣ Removing the Old Furnace: Decommissioning Safely
Mike’s old furnace was a relic — rust on the burner assembly, a cracked heat exchanger, and no variable speed control. Before bringing in the new, he had to carefully remove the old.
🧹 Step-by-Step Removal Process:
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Shut off gas and power at the main valves and breaker panel.
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Label all electrical and thermostat wires before disconnecting.
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Detach vent pipe (the old galvanised flue was brittle and leaking).
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Disconnect the gas supply line with a counter-wrench technique.
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Remove return and supply duct connections.
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Lift and remove the old furnace.
When Mike tilted the old unit, he saw soot buildup and burn marks inside — proof that 20 years of operation had reduced its combustion efficiency.
📘 Reference: Furnace Replacement Safety Steps
🧩 3️⃣ Positioning and Levelling the New Furnace
Getting the new furnace perfectly positioned is the foundation for safe, efficient operation.
⚙️ Step 1: Clear the Base
Mike cleaned the area beneath the furnace, removing dust and debris, and set vibration pads to minimise noise.
📐 Step 2: Level the Unit
He placed a carpenter’s level across the top and adjusted with composite shims until the bubble centred both left-right and front-back.
“I learned that if the furnace isn’t level, the condensate won’t drain properly — it can back up and shut the system down.”
🔩 Step 3: Fasten to the Floor
He used self-tapping screws through the factory base holes into the concrete pad. This prevents vibration and air duct misalignment later.
📗 Reference: How to Install a Furnace Safely
🔧 4️⃣ Gas Line Connection: Getting Combustion Right
Gas connection is not the place to experiment. Even experienced DIYers should consult a licensed professional for verification.
Mike’s Setup Included:
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Black iron pipe with a new shutoff valve and drip leg (per code).
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Yellow Teflon gas-rated tape for threaded joints.
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Leak check using soap solution and manometer pressure testing (11" WC inlet, 3.5" WC manifold).
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Inspection by a certified plumber for $100.
“I wouldn’t risk gas connections on my own. Having a pro check my work gave me peace of mind.”
📘 Reference: NFPA 54 – Fuel Gas Installation Requirements
🌬️ 5️⃣ Venting the Exhaust: Modern PVC Done Right
High-efficiency furnaces like the GMVC96 use two PVC vent pipes: one for intake and one for exhaust. Unlike old systems, they expel low-temperature exhaust gases, so plastic is safe — but the slope and placement are crucial.
Venting Essentials:
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Minimum ¼-inch downward slope per foot toward the furnace (so condensate drains inside).
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Primer and PVC cement at every joint to prevent leaks.
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Termination: at least 12 inches above the snow line and 12 inches apart horizontally.
Mike ran both pipes 18 inches through the rim joist and sealed around the holes with high-temp silicone.
He also used 90-degree elbows to point the exhaust away from windows and fresh-air intakes — a must for safety and compliance.
💧 6️⃣ Condensate Drainage: Where Water Meets Efficiency
Condensing furnaces reclaim so much heat that they literally produce water as a byproduct. Handling this moisture correctly prevents corrosion and system shutdowns.
Mike’s Drain Configuration:
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Factory-installed trap connected to ½-inch vinyl tubing.
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Tubing is routed to a floor drain using a gravity slope.
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Added a condensate neutraliser (filled with limestone chips) to neutralise acidity.
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Secured tubing with clamps to prevent kinks.
“I didn’t realise this furnace would make so much water — almost two gallons a day during cold snaps.”
📗 Reference: Condensate Drainage Guide
⚡ 7️⃣ Wiring the System: Power and Thermostat Connections
Mike’s furnace used a 115V power supply and a low-voltage thermostat circuit.
Steps to Wire Safely:
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Shut off the power at the breaker.
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Connect the line voltage (L1) and neutral to the furnace terminals.
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Ground furnace cabinet with copper wire.
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Connect 24V control wiring:
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R (power)
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W (heat call)
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G (fan)
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Y (cooling)
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C (common)
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He then wired his Honeywell T9 Smart Thermostat, which auto-detected his Goodman’s two-stage heat operation.
📘 Reference: Honeywell – Smart Thermostat Wiring Guide
🔥 8️⃣ Ignition and First Startup: The Moment of Truth
After rechecking every connection, Mike flipped the breaker and gas valve back on. His furnace’s control board performed a self-diagnostic sequence before ignition.
Startup Sequence:
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Inducer motor starts (clears vent).
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Pressure switch confirms airflow.
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Igniter glows orange.
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Gas valve opens.
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Burners ignite in sequence.
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Blower motor starts 30 seconds later.
The system purred quietly. Mike used a combustion analyser to verify:
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CO₂ = 8.7%
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CO = 12 ppm
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Flue temp = 110°F
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O₂ = 6.2%
Everything fell within Goodman’s specs — confirming a clean, efficient burn.
🧠 9️⃣ Testing Airflow and Temperature Rise
AFUE ratings are one thing — real-world comfort is another. Mike tested airflow balance and temperature rise to ensure optimal performance.
| Measurement | Target | Result |
|---|---|---|
| Temp Rise | 35–65°F | 43°F |
| Static Pressure | 0.5” WC | 0.46” WC |
| Blower Amps | <5A | 3.9A |
| Supply Air | 109°F | 111°F |
| Return Air | 68°F | 68°F |
He also verified that the variable-speed ECM blower modulated smoothly between low and high heat modes.
📘 Reference: ACCA – Manual D Air Balancing
🧾 🔟 Code Compliance and Final Inspection
Two days later, a city HVAC inspector arrived for the official inspection.
He checked:
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Proper slope and termination of PVC vents.
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Secure condensate drain routing.
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Gas shutoff and drip leg installation.
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Electrical grounding and labelling.
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CO detector placement.
The system passed on the first inspection.
The inspector even complimented Mike on his clean layout: “Looks like a pro install.”
📗 Reference: EPA – Carbon Monoxide Safety Tips
💡 1️⃣1️⃣ What Mike Learned (and What You Should Know Too)
After dozens of hours reading manuals, watching videos, and double-checking every line, Mike emerged with lessons every homeowner can use:
🔹 1. Measure Twice, Vent Once
PVC slope and distance from openings are not negotiable. The difference between ¼-inch per foot and flat pipe can mean the difference between safe venting and a flooded furnace.
🔹 2. Permits Protect You
Inspections ensure compliance, but they also protect home resale value and insurance coverage.
🔹 3. Levelling Isn’t Optional
If your furnace leans the wrong way, the condensate will flow into the heat exchanger instead of out of it.
🔹 4. Clean Ducts Matter
Even the most efficient furnace can’t perform with dusty, undersized ducts. Mike cleaned his returns before startup.
🔹 5. Maintenance Begins Day One
He scheduled his first professional tune-up six months later to check combustion, tighten fittings, and verify efficiency.
“Installing it taught me how the system breathes,” Mike says. “Now I understand exactly what the annual service does — and why it’s worth every penny.”
💵 1️⃣2️⃣ The Cost Reality: DIY vs. Professional Installation
While Mike wanted the learning experience, he also wanted to know what he saved.
| Category | DIY + Partial Pro Help | Full Professional |
|---|---|---|
| Goodman GMVC96 Unit | $2,075 | $2,075 |
| Gas Line Verification | $100 | Included |
| Electrical Verification | $120 | Included |
| Permits & Inspection | $85 | $85 |
| Labor (DIY) | $0 | $1,700 |
| Total | $2,380 | $3,940–$4,200 |
Mike saved around $1,600 while maintaining warranty coverage (since licensed pros signed off on gas and electric connections).
🌿 1️⃣3️⃣ Energy Savings and Performance Results
After two winters, Mike tracked his energy use with his utility company’s online dashboard. The difference was clear.
| Metric | Old Furnace | New Goodman GMVC96 |
|---|---|---|
| AFUE | 80% | 96% |
| Annual Gas Use | 875 therms | 700 therms |
| Average Monthly Bill | $200 | $155 |
| CO₂ Output | 9,652 lbs | 8,050 lbs |
| Comfort | Uneven | Even, quiet |
| Annual Savings | — | $270 |
| Payback Period | — | 7 years |
📗 Reference: EPA – Greenhouse Gas Equivalencies Calculator
🧭 1️⃣4️⃣ Key Takeaways: Installing for Long-Term Efficiency
✅ 1. Installation = Efficiency
A 96% furnace only performs at 96% when properly vented, levelled, and sealed.
A sloppy install can easily waste 10% of that potential.
✅ 2. Get the Right Support
Even skilled DIYers should involve professionals for combustion, electrical, and code verification.
✅ 3. Think Long-Term
High-efficiency furnaces need proper drainage, filter maintenance, and annual tune-ups to stay peak-performing for 20+ years.
✅ 4. Upgrade Thermostat Tech
Smart thermostats amplify efficiency by learning your habits and reducing runtime during off-hours.
📘 Reference: ENERGY STAR – Smart Thermostat Energy Savings
🧩 1️⃣5️⃣ Conclusion: From Curious Homeowner to Informed Installer
When Mike first started, he thought “installation” meant connecting a few pipes and flipping a switch. By the end, he understood that a furnace is a living system of airflow, pressure, and precision.
He didn’t just install a heating unit — he built a more efficient home.
“I learned that comfort isn’t just about heat. It’s about understanding how every piece — ducts, gas, vents — works together.”
For homeowners considering a replacement, Mike’s experience is proof:
The right furnace, installed correctly, can transform your comfort, efficiency, and monthly bills.
Ready to start your own project? Explore The Furnace Outlet’s Gas Furnace Collection — featuring ENERGY STAR® certified Goodman and Amana systems with detailed installation guides, expert support, and the performance Mike trusted.
