Jake’s proven method for ensuring every 80% furnace vents safely, drafts correctly, and never dumps combustion gases back into the home.
🧭 1. Why 80% Furnaces Fail More Often at the Vent, Not the Burner
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Most installers think an 80% furnace is “simple.” No PVC. No condensate trap. No fancy ECM draft inducer. Just metal pipe and a basic rise.
80,000 BTU 80% AFUE Upflow/Horizontal Single Stage Goodman Gas Furnace - GR9S800803BN
Jake shakes his head every time:
“80% furnaces are simple—until the venting is wrong. Then you get rollout, backdrafting, soot, and ruined heat exchangers.”
80% furnaces rely entirely on:
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Natural draft airflow
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Proper rise angle
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Correct pipe sizing
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Adequate combustion air
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Chimney reliability
If ANY of the above is off even slightly:
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Flue gases spill
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Flame pulls sideways
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Heat exchanger overheats
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CO levels spike
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Draft hood spills
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Upstairs smells like hot metal
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Rollout switch trips
Jake built his Code-Correct Venting Checklist because, in his words:
“A furnace doesn’t know the code. It only knows physics.”
And physics ALWAYS wins.
Jake’s Code-Correct Venting Checklist (The 11 Critical Steps)
Each step comes with real-world explanation + Jake’s field logic.
📏 2. Step 1 — Confirm the Vent Rise Angle: Minimum ¼” Per Foot, Jake Aims for 1/2”
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Code requires:
⬆️ 1/4 inch rise per foot
(Per common mechanical code guidelines)
But Jake installs ½ inch per foot whenever possible.
Why?
Because draft on 80% units is weak compared to modern 90–96% systems.
Draft needs HELP.
Jake’s rule:
“If it barely meets code, it barely drafts.”
Jake’s ideal vent angle:
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Minimum: ¼” per foot
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Preferred: ½” per foot
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Maximum: Enough rise without touching joists or causing uphill dips
What he avoids:
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Dips
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Sags
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Horizontal runs longer than necessary
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Any section where condensation could collect
Even on a dry-vent system like an 80%, dips kill draft.
🌬️ 3. Step 2 — Size the Vent Pipe Correctly (No Guessing, No Eyeballing)
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Jake never sizes a vent based on “what was there before.”
Old systems used:
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Oversized vents
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Metal flues meant for 100k–120k BTU
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Masonry chimneys sized for multiple appliances
When you attach an 80% furnace to an oversized flue → backdrafting begins.
Jake’s rule:
✔️ Match the pipe to BTU
For an 80,000 BTU furnace like the GR9S800803BN, Jake typically uses:
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3-inch vent for short runs
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4-inch vent for longer runs
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Never bigger unless chimney requires it
Oversized vent = cold flue = NO draft.
🚫 4. Step 3 — NEVER Reduce Vent Diameter
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Jake refuses to reduce vent size downstream.
He avoids:
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4” to 3” reducers
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6” masonry flues reduced to 4” connector
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Shared water heater vents where furnace is undersized
Reduction = turbulence = backdraft.
Jake says:
“Reducing a vent is like pinching a straw. It’ll blow back in your face.”
🏚️ 5. Step 4 — Inspect the Chimney (Most Common Backdrafting Cause)
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Older chimneys cause the most problems.
Jake finds:
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Oversized masonry flues
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Flues colder than outdoor air
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Reverse drafting due to cold air falling
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Bird nests
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Lack of clay liner
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Mortar blockages
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Crumbling interior walls
If the chimney is oversized or cold, he installs:
✔️ Stainless steel chimney liner
Corrects:
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Draft speed
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Flue temperature
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Condensation
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CO spillage
Jake calls this:
“Putting a warm pipe inside a cold box.”
It works. Every time.
🔥 6. Step 5 — Check the Draft Hood for Spillage
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After first fire, Jake places:
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A lighter flame
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A smoke pen
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Or a tissue test
Near the draft hood.
If smoke/tissue falls or lingers → backdraft.
If flame pulls inward → proper draft.
Jake says:
“The draft hood is the furnace’s throat. If it’s coughing, something’s wrong.”
He tests with:
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Door open
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Door closed
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Blower on
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Blower off
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Dryer running
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Exhaust fan running
Why all those?
Because negative pressure from other appliances causes rollout.
🌀 7. Step 6 — Perform the Draft Pressure Test With a Manometer
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Jake measures draft in inches WC.
Typical natural draft target:
✔️ -0.01” to -0.04” WC
(depending on code & manufacturer)
Jake’s ideal range:
-0.02 to -0.03" WC
Too weak? Backdraft danger.
Too strong? Flame distortion, noise, and heat exchanger stress.
He tests draft:
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At the breach
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Mid-run
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End of chimney (via port)
Jake NEVER signs off until draft stays steady for 5–7 minutes.
🪟 8. Step 7 — Verify Combustion Air (The Silent Backdraft Killer)
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Furnaces need a LOT of air.
For 80k BTUs:
4,000 cubic feet of combustion air
OR a properly sized combustion air duct.
Jake tests by:
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Opening the closet door
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Closing the closet door
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Running a smoke pen
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Watching flame stability
If flame wobbles → insufficient air → backdraft.
Jake installs:
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Louvered doors
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Upper/lower vents
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Dedicated combustion air piping
He has lost count of how many “bad venting” issues were actually combustion air issues.
🧯 9. Step 8 — Remove All Vent Dips, Sags, and Inverted Joints
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Jake inspects the vent like a roof inspector.
What he fixes:
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Dips
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Belly sags
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Inverted elbows
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Condensation traps
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Screws protruding inside pipe
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Sharp turns beyond 90° total equivalent
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Poor transitions
Dips cause:
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CO pooling
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Delayed draft
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Cold spots
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Frost formation in chimneys
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Puffing and rollout
He re-hangs vent sections with:
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Metal strap
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Vent support brackets
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Rigid braces
Jake says:
“The vent should look like a smooth highway ramp, not a pothole street.”
🧱 10. Step 9 — Seal All Vent Connections (But Not the Draft Hood!)
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Jake uses:
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Foil tape
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High-temp silicone (where code allows)
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Sheet metal screws
He seals:
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Elbows
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Joints
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Transitions
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Flue collar connections
He does NOT seal:
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Draft hood edges
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Relief openings
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Relief ports
Sealing a draft hood violates function AND code.
🧰 11. Step 10 — Test Under Full System Load
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Jake performs:
✔️ High-heat run for 10 minutes
To ensure draft increases, not decreases.
✔️ Blower-only mode
Checks if static pressure reverses draft.
✔️ Dryer + bathroom fan test
Simulates real-world negative pressure.
If the draft reverses when exhaust fans run → fix the air or venting path.
Jake says:
“Test like a homeowner, not an inspector.”
Inspectors test ideal conditions.
Jake tests normal chaos.
📋 12. Step 11 — Jake’s Final 9-Point Venting Sign-Off Checklist
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Jake won’t sign his name unless:
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✔️ Proper rise: ¼–½” per foot
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✔️ Correct vent diameter
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✔️ No reductions
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✔️ No sags or dips
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✔️ Draft hood pulls consistently
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✔️ Manometer draft in correct range
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✔️ No backdrafting under ANY appliance load
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✔️ Chimney inspected or lined
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✔️ Combustion air verified
He says:
“If the vent is right, the furnace behaves. If the vent is wrong, the furnace screams for help.”
And he’s right.
📚 13. External Verified Resources (Up to 6)
All safe, reliable, and non-competing.
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ENERGY.gov — Furnace venting basics
https://www.energy.gov/energysaver/furnaces-and-boilers -
ASHRAE Standards — Ventilation & combustion air requirements
https://www.ashrae.org
🏁 14. Final Word From Jake
Jake teaches every apprentice the same thing:
“Venting is where 80% furnaces live or die.
You don’t install a vent—you design it.”
With Jake’s Code-Correct Venting Checklist:
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No rollout
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No spillage
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No cold flue
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No CO risk
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No callbacks
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No angry inspectors
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No homeowner complaints
Just a quiet, safe, perfectly drafting 80% furnace—exactly how Jake installs every one.
Buy this on Amazon at: https://amzn.to/3L2nAfF
In the next topic we will know more about: Jake’s Precision Tool Pass: How to Use the Amazon Torch/Detection Kit for Perfect Burn Patterns and Clean Ignition
