Professional Installation Rules: How Pros Install the Goodman 96% Furnace

If you’re putting a Goodman 96% AFUE furnace in a home and you’re not following the rules I’m about to lay out, you’re not “a little off.” You’re wrong.

I’m Jake, and this is written in an accountability tone on purpose—because a 96% condensing furnace is not a plug-and-play appliance. Bad installs crack heat exchangers, flood basements, freeze coils, cause nuisance lockouts, variable speed, and in the worst cases, create unsafe conditions.

This article is not a DIY wiring or gas-piping guide. It’s a professional accountability checklist: what a real pro must be doing when installing a Goodman 96% furnace, especially models like GM9S96/GMVC96/GR9T96, and how you—as a tech, company owner, or informed homeowner—can hold the work to a higher standard.

I’m going to cover:

Venting mistakes (slope, elbows, PVC size)
Proper drain routing for a condensing furnace
A coil matching compatibility chart and AHRI verification
Correct heat rise testing procedure
Gas line sizing requirements
Airflow testing with a manometer
Electrical and grounding requirements
Horizontal install do’s and don’ts

And I’m going to call out the shortcuts that separate hacks from professionals.

1. Rule #1: The Manual Is Law (For Real)

For Goodman 96% furnaces, the installation manual and technical manual are not suggestions; they’re binding. Pros should have the PDF open or the book in hand—start to finish.

You can see exactly the kind of venting, wiring, and rating-plate data I’m referencing in Goodman’s own documentation, for example:

Those manuals clearly spell out:

Vent pipe diameters (2" or 3" PVC, depending on input, run length, and elbows) Goodman Manufacturing
Approved materials (typically Schedule 40 PVC, CPVC, or ABS where allowed by code)
Maximum equivalent vent length
Rated heat rise and maximum external static pressure
Electrical data (voltage, blower amps, circuit protection, wire size)

If your installer isn’t referencing those documents, they’re guessing. Accountability starts with: “Show me in the Goodman book where it says that.”

2. Venting Mistakes: Slope, Elbows, PVC Size

Condensing furnaces live or die on venting. At 96% AFUE, you’re pulling so much heat out of the exhaust that water condenses in the pipes constantly. The vent system has to drain that condensate and move flue gases safely.

2.1 PVC Diameter & Length

Goodman’s 96% lines typically require 2" or 3" PVC based on:

Furnace input BTU
Total equivalent vent length
Number of elbows
Whether it’s a one-pipe or two-pipe system

Wrong pipe size = wrong airflow in the vent. Too small, and you get excessive restriction and potential fault codes. Too large in short runs, and velocity can drop so low that condensate pools and flue gases struggle.

Accountability move (Jake style):
Ask the installer:

“Show me the table in the Goodman manual you used to pick 2" vs 3" and how you counted elbows.”

If there’s no table and no math, it’s not professional.

2.2 Slope and Trap Points

Venting on condensing furnaces must be pitched back toward the furnace or designated drain point (typically ¼" per foot unless the manual states otherwise). This is so condensate:

Flows toward the drain system, not back to the outdoors
Does not collect in low points and choke off the vent

Pooling condensate in vent elbows or sags causes gurgling, corrosion, and repeated pressure-switch trips.

2.3 Elbow Count and Equivalent Length

Every 90° elbow adds “equivalent feet” to the vent run. Goodman tables apply total equivalent length (straight run + elbow allowance), and pros must:

Count every elbow
Convert to equivalent length per the manual
Confirm they stay within the max vent length

If someone says: “We use 2" on everything, it’s fine,”—nope. That’s not fine. That’s lazy.

3. Proper Drain Routing for a Condensing Furnace

A 96% Goodman furnace generates a lot of condensate, especially in long run times. That water is mildly acidic and must be routed carefully to prevent equipment damage and flooding.

Key principles across codes and best practices:

Dedicated drain line from the furnace’s internal trap and secondary ports
Appropriate slope (¼" per foot minimum) toward the termination (floor drain, condensate pump, approved indirect connection)
A trap as designed by the manufacturer (do NOT “wing it” with random fittings)
Avoiding kinks, elevated runs, or long flat sections where water can sit
Protection from freezing in unconditioned spaces
Neutralizer kits if required by local plumbing code when tying into certain drains, acceleratenetzero.com

A solid overview of high-efficiency condensate best practices is here:

Accountability Jake check:

Is the drain line pitched?
Does it terminate legally (no direct tie into a pressurized waste line)?
Is the trap factory-configured or field-hacked?

No pitch + no trap = callback waiting to happen.

4. Coil Matching Compatibility Chart (And Why AHRI Matters)

A Goodman 96% furnace rarely runs alone—it’s part of a matched system that includes:

Outdoor condenser or heat pump
Indoor evaporator coil
Furnace and blower

Performance ratings (SEER2, EER2, capacity) are based on matched combinations listed in the AHRI Directory.

Pros should confirm compatibility with AHRI, not guess. You can do this using:

4.1 Sample Compatibility Chart (Conceptual Example)

Note: Exact model matches must be verified in AHRI; this is a conceptual example of how a pro should think.

Furnace (96% AFUE)	Input BTU	Typical Match Range (Cooling Tons)	AHRI Match Required?	Notes
40–60k Goodman 96%	40–60k	1.5–3.0 tons	Yes	Smaller cabinets, ideal for smaller homes
80k Goodman 96%	80k	2–4 tons	Yes	Common for mid-size homes
100k+ Goodman 96%	100–120k	3–5 tons	Yes	Larger homes / colder climates

A good pro doesn’t say “3-ton coil, 3-ton condenser, we’re good.” They:

Verify the exact model numbers in the AHRI directory. AHRI
Confirm the AHRI Certificate shows the performance and combination.
Check Goodman documentation or distributor tools (like local AHRI match tools).

If your installer can’t produce an AHRI certificate for the furnace + coil + condenser combination, they’re leaving efficiency and sometimes rebates on the table.

5. Correct Heat Rise Testing Procedure (Accountability Version)

The heat rise is the temperature difference between the return air and supply air with the furnace firing. Goodman prints an acceptable range (e.g., 35–65°F) right on the rating plate and in the installation manual.

At a professional level, this is non-negotiable:

Furnace runs at full heating input (no short cycling, proper gas pressure set by a licensed pro).
Return-air temperature is measured in the return plenum/duct, away from the furnace cabinet.
Supply-air temperature is measured in the supply trunk, a few feet downstream from the furnace, not in the heat exchanger cell.
Heat rise (ΔT) = Supply temp − Return temp.
Tech compares ΔT with the nameplate range and adjusts airflow, not firing rate, to dial it in (within Goodman’s blower speed tables). documents.alpinehomeair.com

Tips:

Too high ΔT (air too hot) → airflow is too low, leading to exchanger stress, limiting trips.
Too low ΔT (small temp difference) → airflow may be too high, reducing efficiency and comfort.

Accountability Jake question:

“What heat rise did you measure, and where does that fall against the Goodman rating plate?”

If they don’t know, they didn’t finish the job.

6. Gas Line Sizing Requirements

Gas piping isn’t “close enough is fine.” It’s code-driven engineering. Pros must size lines according to NFPA 54 (National Fuel Gas Code) or the applicable mechanical code, using approved tables. NFPA Document Information Files

Good references (for pros and inspectors):

What a Pro Must Do (High Level)

Determine the total BTU load on the gas system (furnace + water heater + range, etc.).
Determine gas pressure at delivery.
Measure or estimate the longest run and total equivalent length (including fitting allowances).
Use NFPA 54 tables or approved software to choose the minimum pipe diameter for each segment. American Gas Association

Under-sized gas piping can:

Starve the furnace at high fire
Cause low manifold pressure
Lead to poor combustion and high CO

If gas is touched, it must be done by a licensed professional, period. Homeowners, this is not DIY territory.

7. Airflow Testing with a Manometer (Static Pressure Accountability)

You can’t “eyeball” airflow. Goodman clearly specifies the maximum total external static pressure (TESP) in the technical data. Goodman Manufacturing

Real pros measure:

Return static (negative)
Supply static (positive)
Add them to get TESP

Why it matters:

If TESP exceeds the nameplate limit, the blower can’t move rated CFM.
High static = noisy ducts, stressed motors, poor comfort, coil freeze risk.

For pros, this is standard ACCA-quality work: ACCA HVAC Blog

A manometer reading that proves the system is within Goodman’s rated static is part of the install, not a bonus.

Accountability questions for your installer:

“What was the total external static pressure you measured?”
“How does that compare to the Goodman-rated maximum?”
“Where did you drill your test ports?”

If there’s no manometer on site, that’s a red flag.

8. Electrical + Grounding Requirements

Goodman 96% furnaces are designed for a 115 V, 60 Hz, single-phase supply with proper overcurrent protection and grounding.

Professionals must:

Run a dedicated circuit sized per the nameplate and electrical code (commonly via NEC 110/422/430, as adopted locally).
Use the correct breaker or fuse size specified in the manual. HVAC Direct
Ensure proper equipment grounding conductor is installed.
Respect polarity and neutral connections.
Make low-voltage thermostat wiring neat, strain-relieved, and properly terminated.

Incorrect grounding or miswired neutrals can create:

Nuisance board failures
EMI noise issues
Shock hazards

Again, this needs a licensed electrician or a properly licensed HVAC pro. Homeowners should use electrical requirements as a checklist, not as instructions.

9. Horizontal Install Do’s and Don’ts (Goodman 96% Furnace)

Horizontal installs crank the difficulty up a notch. The Goodman 96% furnace can often be installed upflow, downflow, or horizontal, but each orientation has specific rules in the manual.

Do’s

Do verify the orientation is permitted for that model (upflow/horizontal left, horizontal right, etc.).
Do follow Goodman’s clearances to combustibles and service access.
Do reconfigure the condensate trap and drain for horizontal operation so water flows out, not into the cabinet. afmplumbingheating.com
Do support the furnace along its length so the case doesn’t sag.
Ensure the secondary drain or float switch is properly piped for coil sections above the furnace.

Don’ts

Don’t flip the furnace into horizontal without re-reading the specific horizontal section of the Goodman manual.
Don’t let condensate run back toward the heat exchanger.
Don’t ignore filter access—horizontal installs still require accessible filtration.
Don’t bury the furnace in blown insulation with no service platform or access.

Horizontal setups are where you see a lot of “it kind of fits” thinking. Accountability Jake says: if it looks like a garage shelf job, it’s wrong.

10. Accountability Checklist: How Pros Should Install a Goodman 96% Furnace

Here’s your non-negotiable checklist. This is how a professional installation of a Goodman 96% furnace should look on paper:

Manual in hand – The Goodman 96% manual is open and followed, not ignored.
Venting sized and sloped correctly – 2" or 3" PVC selected from the Goodman tables; elbows counted; slope back to the furnace or approved drain.
Condensate drain designed properly – Trap configured per manufacturer, slope maintained, neutralization considered, legal discharge location.
Coil and condenser AHRI-matched – AHRI certificate printed or saved, matching furnace + coil + outdoor unit.
Heat rise measured and documented – Supply/return temps recorded; ΔT verified against rating plate; blower speed adjusted accordingly.
Gas piping sized per NFPA 54 – Total BTU load, length, and pressure considered; gas line sized from code tables or engineering software.
Static pressure measured with a manometer – Test ports drilled; TESP compared to Goodman max; airflow verified against Manual D design.
Electrical and grounding correct – Dedicated circuit; breaker/fuse per nameplate; proper ground and neutral; clean low-voltage wiring.
Orientation rules followed – Horizontal, upflow, or downflow setup strictly per Goodman’s orientation diagrams. ManualShelf

If any of these are missing, that’s not a professional install—that’s a liabilit

Conclusion

A Goodman 96% furnace is an excellent piece of equipment when it’s installed by the book. If you’re a tech, this is your checklist. If you’re a homeowner, this is your accountability script. Anyone installing a 96% furnace without following these rules isn’t doing “good enough.” They’re doing it wrong—and you’re the one who lives with the consequences.

In the next blog, you will learn about Best AC Matches for the 60k Furnace (1.5–3 Ton Systems)