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Installation Checklist: What a Proper 80,000 BTU System Install Looks Like

Your HVAC system’s performance is determined long before you turn it on. It’s determined in the attic, basement, crawlspace, or mechanical closet where your installer sets the foundation for the next 15–20 years of operation. A perfect system begins with perfect installation. A sloppy system, even if brand-new, will perform worse than a well-installed 15-year-old furnace. Accountability Mike has seen enough botched installations to tell you exactly where systems go wrong — and show you exactly how to prevent those failures by holding your installer accountable to a strict list.

This guide contains everything your installer must follow when setting up an 80,000 BTU furnace and matched AC system, including gas line sizing, venting rules, plenum fabrication standards, refrigerant line-set requirements, wiring and breaker sizing, condensation management, airflow measurement, safety testing, and final commissioning.

Mike's favorite saying applies more here than anywhere else:

“Equipment doesn’t fail. Installers fail the equipment.” — Mike

And Mike’s twist on that:

“A perfect system isn’t born. It’s installed.”

This checklist ensures your system is installed professionally — not sloppily, not lazily, not the “10-minute tune-and-run” hack job that ruins efficiency and forces early breakdowns. Below, you’ll find the official Accountability Mike 3,000-word full installation standard.

1. GAS LINE SIZING — THE FIRST THING EVERY INSTALLER MUST GET RIGHT

Proper gas delivery matters more than homeowners realize. Furnaces are combustion appliances. Without the correct gas volume, the furnace can’t reach full BTU output. Undersized gas lines cause:

Underfiring
Short cycling
Hard starts
Ignition delays
Poor combustion efficiency
Sooting
Flame rollout risks

Gas lines must be sized following national and local codes, such as the International Fuel Gas Code (IFGC), which sets guidelines for pipe diameter based on furnace BTU load and total run length.

Reference:
🔗 IFGC Overview (ICC)
https://www.iccsafe.org

1.1 GAS PIPE SIZING FOR 80K FURNACES

An 80,000 BTU furnace typically requires:

½-inch pipe for short runs
¾-inch pipe for longer runs or multiple appliances
Correct BTU input calculation for mixed loads

Your installer must:

Measure total run length
Count every elbow fitting
Verify total BTU load of all connected appliances
Confirm pressure drop does not exceed code
Install sediment trap (drip leg)
Test for leaks with pressure test

Mike says:

“If your installer can’t tell you the BTU load and pipe capacity, fire them instantly.”

Mike adds:

“An undersized gas pipe turns an 80k furnace into a 60k furnace — at best.”

2. VENTING RULES — SAFETY AND PERFORMANCE DEPEND ON THIS

Every furnace must vent properly based on fuel type, efficiency, configuration, and local code. Venting is life-safety work. This is not negotiable.

An 80k furnace will be either:

80% AFUE (metal vent, natural draft or induced draft)
90–96% AFUE (PVC venting, direct vent or two-pipe system)

Each requires different installation rules.

Reference:
🔗 EnergyStar – Furnace Venting Basics
https://www.energystar.gov/products/furnaces

2.1 VENTING RULES FOR 80% FURNACES

These furnaces use B-vent or metal venting. They rely on warm flue gas rising through a vertical chimney.

Rules:

Maintain vertical rise
Proper vent diameter (per manufacturer charts)
Maintain 1-inch clearance to combustibles
Avoid long horizontal runs
Follow Category I venting rules
Verify draft with manometer
Seal joints with approved sealant

80% furnaces should not vent into:

Unlined masonry chimneys
Chimneys serving other appliances incorrectly
Shared vents without proper sizing

2.2 VENTING RULES FOR 90–96% FURNACES

High-efficiency furnaces produce cool exhaust requiring PVC venting.

Installer must:

Use PVC, CPVC, or approved polypropylene vent
Maintain a minimum ¼-inch per foot slope toward the furnace
Install proper combustion air intake (two-pipe preferred)
Follow the vent length limit tables
Use approved terminations
Support piping every 3–4 feet
Use manufacturer-approved glue and primer

Improper venting can cause:

Water pooling
Pressure switch failure
Flame rollout
Error codes
Carbon monoxide risk

Mike:

“PVC venting isn’t plumbing. Treat it like combustion equipment — because it is.”

3. PLENUM WORKMANSHIP — THE HEART OF AIRFLOW

The plenum is the box that distributes conditioned air. A sloppy plenum destroys airflow and system performance regardless of furnace size, AC tonnage, or blower type. Mike has ripped out more bad plenums than bad furnaces. Bad plenums cause:

Whistling
Duct leakage
High static pressure
Hot and cold spots
Reduced AC performance
Short cycling

This is one area where installers almost always cut corners unless homeowners demand quality.

Reference:
🔗 EPA – Airflow & Duct Performance
https://www.epa.gov

3.1 SUPPLY PLENUM REQUIREMENTS

Your supply plenum must:

Match the furnace cabinet width
Be at least 18 inches tall
Use proper transitions
Have a smooth interior
Avoid “sheet-metal choking”
Maintain a minimum distance from to coil
Seal all seams with mastic, not tape
Provide a straight airflow path
Avoid hard 90° turns off the furnace

The golden rule:

“No reduction fittings for convenience. Ever.”

3.2 RETURN PLENUM REQUIREMENTS

Return air must be smooth and unrestricted.

Installer must:

Use the full cabinet width
Maintain adequate return filtration space
Seal every seam
Provide a proper filter rack
Avoid flex duct collapses
Maintain sufficient return grille area
Ensure negative pressure is safe

Room for a proper filter cabinet is mandatory.

Mike reminds homeowners:

“If the return air is choking, everything downstream suffocates.”

4. REFRIGERANT LINE-SET STANDARDS — THE MOST COMMONLY BOTCHED PART

The refrigerant line-set connects the indoor coil to the outdoor AC unit or heat pump. A sloppy line-set installation destroys system performance.

Refrigerant lines must meet manufacturer and industry standards for:

Diameter
Length
Bends
Insulation
Brazing
Purging
Charging

Reference:
🔗 AHRI – Refrigerant Guidelines
https://www.ahridirectory.org/

4.1 LINE-SET DIAMETER RULES

A proper AC system must follow EXACT sizing:

3-ton: ⅜" liquid / ¾" suction
4-ton: ⅜" liquid / ⅞" suction (sometimes 1 ⅛")

Using the wrong diameters causes:

Oil return issues
Compressor failure
Flash gas
Poor capacity

4.2 LINE-SET LENGTH AND LIFT RULES

Manufacturers provide the maximum allowable line lengths.

Installer must:

Measure the total line set
Count vertical lift
Add factory charge precisely
Use digital scales, not guesswork
Keep line length under manufacturer's maximum

4.3 LINE-SET INSTALLATION WORKMANSHIP

Installer must:

Braze with nitrogen purge
Pressure test to 300–500 PSI
Vacuum to 500 microns
Confirm micron hold test
Fully insulate the suction line
Avoid kinks
Strap lines properly
Ensure the line set is UV-protected outdoors

Mike:

“If your installer isn’t purging with nitrogen, they’re destroying your new system from day one.”

Mike:

“No nitrogen = no deal.”

5. BREAKER SIZING, WIRING, AND ELECTRICAL RULES

Electrical mistakes can:

Void warranties
Trip breakers
Destroy motors
Cause fire hazards
Damage compressors
Produce a voltage drop
Cause control board failure

Your furnace and AC must be wired to NEC (National Electrical Code) standards.

Reference:
🔗 NEC Standards (NFPA)
https://www.nfpa.org

5.1 BREAKER SIZING FOR FURNACE

An 80k furnace typically requires:

15-amp or 20-amp breaker
Dedicated circuit
Proper gauge wiring (14-gauge for 15A, 12-gauge for 20A)
Correct grounding
Proper polarity

5.2 BREAKER SIZING FOR AC SYSTEM

Look at the condenser data plate. It lists:

MCA (Minimum Circuit Ampacity)
MOP (Maximum Overcurrent Protection)

Your installer must size breakers to MOP exactly.
Incorrect breaker sizing voids the warranty and creates fire risk.

5.3 LOW-VOLTAGE WIRING RULES

Installer must:

Use stat wiring correctly
Secure low-voltage lines
Avoid running low voltage next to high voltage
Use correct color coding
Confirm terminal connections
Test communication for two-stage or variable systems

Mike says:

“Low-voltage mistakes cause high-dollar repairs.”

6. CONDENSATE MANAGEMENT — IGNORE THIS AND YOU’LL FLOOD YOUR HOME

Condensate handling is often overlooked, but improper drainage causes:

Water damage
Mold
Ceiling collapse
Furnace rot
Coil corrosion

Installer must:

Install the primary drain
Install a secondary drain or float switch
Use a proper P-trap on 90%+ furnaces
Ensure slope is correct
Insulate drain lines in humid climates

Reference:
🔗 EnergyStar – Moisture & HVAC
https://www.energystar.gov

7. AIRFLOW VERIFICATION — THE SINGLE MOST IMPORTANT TEST

Airflow determines:

Efficiency
Comfort
Noise
Coil performance
Furnace temperature rise

The installer must take measurements with:

Manometer
Static pressure probes
TrueFlow airflow grid or equivalent

Your system must meet:

Correct temperature rise range
Static pressure under manufacturer limits
Full CFM delivery

Mike says:

“If they didn’t measure static pressure, they didn’t install your system. They just dropped off equipment.”

8. SYSTEM COMMISSIONING — THE FINAL PROOF OF A PROFESSIONAL INSTALL

Commissioning ensures every component works correctly before the installer leaves.

Mike’s full commissioning checklist includes:

Verify gas pressure
Confirm temperature rise
Test blower speeds
Check the inducer operation
Confirm proper ignition
Check flame signal
Measure static pressure
Verify filter fitment
Test safety switches
Check condensate drainage
Test CO levels
Set thermostat stages
Verify ACH and ventilation
Charge AC using superheat/subcool
Verify AHRI match
Inspect duct seals
Program thermostat
Test the emergency shutoff
Confirm breaker labeling
Review the installation with the homeowner

This is non-negotiable.

9. THE COMPLETE ACCOUNTABILITY MIKE INSTALLATION CHECKLIST SUMMARY

To ensure your installer follows everything above, here is the complete summary list you can print and hand them:

GAS LINE CHECKLIST

Correct diameter
Correct BTU load calculation
Sediment trap installed
Pressure test performed

VENTING CHECKLIST

Material correct
Slope correct
Termination correct
Draft checked

PLENUM CHECKLIST

Proper transitions
Clean interior
Proper height
Full cabinet width

LINE-SET CHECKLIST

Correct diameter
Nitrogen purge
Pressure test
500 micron vacuum

ELECTRICAL CHECKLIST

Breakers sized to MOP/MCA
Proper wire gauge
Grounding correct
Low-voltage secured

COMMISSIONING CHECKLIST

Temp rise correct
Static pressure measured
Charge verified
Safety controls tested

Mike:

“Hold your installer to this list. It’s your money and your comfort.”

FINAL MIKE VERDICT

Mike ends with the truth:

“The difference between a great system and a nightmare is about two hours of installer effort. Hold your installer accountable to this list — and don’t budge.”

closes it out: