Why Your Furnace Venting Matters: Correct Intake & Exhaust Installation for High-Efficiency Systems
Real Case Study: Improper Vent Termination Causing Water Pooling
High-efficiency furnaces—such as the Ruud R962V, Goodman, Carrier, Lennox, and other modern 90%+ AFUE models—depend on proper PVC vent installation to operate safely and efficiently. But in many homes, the vent pipes are installed incorrectly, creating problems such as:
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Water collecting inside the exhaust
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Back-drafting
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Poor combustion
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Icing and blockage in winter
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Premature damage to the furnace
A recent real-world example clearly illustrates these issues.
Case Study: Incorrect Installation Found Outside a Customer’s Home
In the provided photo, several installation errors are immediately visible:
1. Intake and exhaust are on the same horizontal plane
Manufacturers require at least 9 inches of vertical separation between them.
Why?
Because exhaust gases can be pulled directly into the intake, causing oxygen-starved combustion and high CO.
2. The intake termination uses a 45° elbow no stainless-steel protective screen.
A 45° opening no stainless-steel protective screen:
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Allows animals and leaves to enter
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Provides no protection from wind pressure
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Breaks manufacturer recommendations for high-efficiency systems
The intake should use a 45°or 90° turned-down termination with a protective screen.
3. The exhaust termination incorrectly uses a PVC tee
This is one of the most common but most dangerous mistakes.
A tee is NOT a vent cap.
From an aerodynamic perspective:
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A tee creates internal turbulence
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Moisture cannot drain effectively
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Condensation accumulates inside
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Flow velocity drops sharply
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Pressure pulses can force exhaust back toward the furnace
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In cold weather, it forms ice at the opening
All of this leads directly to the problem mentioned: water pooling inside the exhaust pipe.
4. The openings are also directly above—one on top, one below—creating vertical interference
This violates nearly every manufacturer’s installation guide.
5. No stainless-steel mesh protection
Without a screen:
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Birds
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Wasps
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Rodents
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Leaves and debris
can all enter the vent pipes, leading to dangerous blockages.
Why Aerodynamics Matter in PVC Furnace Venting
PVC intake/exhaust systems rely on:
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Controlled airflow
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Stable pressure
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Proper drainage
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Minimal turbulence
But when using a tee or an upward-facing elbow, airflow becomes disrupted.
Aerodynamic Consequences of a Tee:
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Creates vortex turbulence inside the fitting
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Reduces exhaust velocity
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Causes condensation to stall and collect
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Increases risk of water freezing at the opening
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Raises back-pressure inside the furnace
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Leads to error codes such as pressure switch faults
This is why manufacturers and HVAC professionals insist on a downward-facing 90° vent termination.
Correct Installation: How It SHOULD Look
✔ 1. Exhaust on the bottom, intake above it
Minimum vertical separation: 9 inches
Reason: Prevent exhaust re-entrainment.
✔ 2. Both terminations should use a 90° elbow pointing downward
This design:
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Protects from snow
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Prevents rain entry
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Allows condensation to drain
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Reduces wind interference
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Improves airflow stability
✔ 3. Use a stainless-steel screen on both pipes
Prevents animals and debris from entering.
✔ 4. Avoid using tees as vent caps—ever
They do not meet airflow requirements.
✔ 5. Maintain correct pitch
The exhaust should always pitch back toward the furnace (¼" per foot) to allow drainage.
Recommended Product: Stainless-Steel Screen 90° PVC Termination Cap
Most problems like this can be solved by using a proper vent termination cap designed specifically for high-efficiency furnaces.
⭐ Recommended: 90° Stainless-Screen Vent Termination Cap
Amazon Link:
PVC termination vent with stainless steel screen,90 Degrees,1pcs,For 2“ DWV PVC Pipe,Roof Vent Cap,Installation not Required That Elbow
Why homeowners love it:
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Designed specifically for 2" DWV PVC
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Stainless steel screen keeps animals & leaves out
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Downward-facing 90° elbow prevents snow blockage
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No coupling or elbow required
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Zero-tools installation
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Thousands of satisfied customers
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High Amazon ratings
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Used by HVAC professionals nationwide
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Safety
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Durability
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Proper airflow
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Freeze protection
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Long-term reliability
Also Available at LGQF-LL.com
For those looking to order directly, visit:
Our vent caps are engineered for:
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Goodman
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Carrier
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Trane
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Lennox
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Ruud
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Rheem
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York
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All 90%+ high-efficiency furnaces
Step-by-Step Installation Guide
Tools needed:
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None (product installs by hand)
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Optional: silicone for added wall seal (not required for vent cap)
Step 1 — Remove the existing fittings
Remove the 45° intake elbow and the tee on the exhaust.
Step 2 — Check pipe pitch
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Exhaust: pitched toward furnace
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Intake: pitch doesn’t matter much, but avoid low points that collect condensation
Step 3 — Install the 90° downward caps
Push-fit installation. No glue required.
Step 4 — Ensure correct vertical spacing
Position intake above the exhaust (minimum 9").
Step 5 — Verify airflow and clearances
Make sure:
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Exhaust blows freely downward
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Intake is not facing snow, soil, or obstructions
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No siding or vegetation blocks air movement
Step 6 — Run the furnace and check
Make sure:
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No gurgling sounds
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No water dripping from the vent
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No pressure switch error codes
Risks of Incorrect Vent Installation
If the venting remains as shown in the photo:
❌ Water accumulation
Leading to pipe freezing and furnace shutdown.
❌ Back-drafting
Dangerous CO risk.
❌ Pressure switch failures
Causing the furnace to refuse to ignite.
❌ Blocked vent alarm / no heat
Especially in winter.
❌ Premature furnace damage
The most expensive outcome.
Conclusion: Proper Vent Termination Is Not Optional
High-efficiency furnaces rely on correct airflow and proper vent termination for safe operation.
Using tees, incorrect angles, or placing intake and exhaust too close together creates real hazards—most of which can be prevented with the right vent cap.
For a safe, compliant, durable solution, we recommend:
Amazon:
PVC termination vent with stainless steel screen,90 Degrees
Direct Store:
Protect your furnace.
Protect your home.
And avoid expensive winter breakdowns.