Does an R-32 Gas Furnace Need Special Venting? Tony Explains PVC, Condensate & Code Requirements
Homeowners upgrading to a 100,000 BTU R-32 gas furnace often ask Tony the same thing:
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“Does R-32 change the venting?”
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“Do I need special PVC?”
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“Is the refrigerant flammable — does that affect the exhaust?”
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“Are code rules different now?”
Tony’s answer is simple:
“R-32 has NOTHING to do with your furnace vent. The venting follows furnace efficiency — not refrigerant.”
R-32 is the refrigerant in the AC/heat pump side, not the fuel for the furnace.
What determines your venting system is AFUE — whether the furnace is 80% or 95–98% condensing.
Still, because the R-32 product lines are newer and designed for next-gen HVAC systems, the furnaces built alongside them often follow updated venting, combustion air, and code standards.
This blog breaks down exactly what matters — vent pipe types, combustion air rules, condensate handling, safety codes, PVC requirements, and what Tony checks BEFORE and AFTER installation.
1. First Rule: R-32 Does NOT Change Your Furnace Venting System
Let’s clear this up immediately:
✔ The FURNACE burns natural gas or propane
✔ The refrigerant NEVER touches the heat exchanger
✔ Venting has NOTHING to do with refrigerant choice
Venting is dictated by:
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AFUE rating
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combustion design (open, sealed, or induced draft)
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condensing vs. non-condensing design
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manufacturer specifications
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local/mechanical codes
R-32 doesn’t enter the conversation.
It’s all about furnace type.
[Gas Furnace Venting & Combustion Air Code Requirements]
2. 80% (Non-Condensing) Furnaces: Metal Vent Pipe
If your R-32-compatible furnace is an 80% AFUE model, it uses category I metal venting.
✔ Uses single-wall or double-wall metal
✔ Must vent into an approved chimney or B-vent
✔ Requires proper rise/slope
✔ Pulls combustion air from basement or utility room
✔ No PVC allowed
✔ No condensate drain
Tony checks:
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vent draft
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corrosion
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chimney liner condition
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vent size
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vent height
If venting is too small, too large, or corroded → backdrafting occurs.
Backdrafting = carbon monoxide risk.
This is why Tony inspects every inch from furnace to termination.
3. 95%+ (Condensing) Furnaces: PVC or CPVC Vent Pipe
Most R-32 furnace lineups include high-efficiency 95–98% AFUE models, which require:
✔ PVC venting (Schedule 40)
✔ CPVC (if required by manufacturer)
✔ Polypropylene (PPS) in some jurisdictions
Tony strictly follows manufacturer tables for:
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pipe diameter
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vent length
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total elbows
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slope
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termination clearances
High-efficiency venting includes:
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intake pipe (combustion air)
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exhaust pipe
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condensate drainage
PVC venting is cool to the touch because the secondary heat exchanger extracts heat before gases exit.
These furnaces DO create acidic condensate — and that must be handled correctly.
4. Combustion Air: Where the Furnace Gets Oxygen
Combustion air rules depend on furnace type.
✔ 80% Furnaces
Pull combustion air from indoors (open combustion).
Room must meet:
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minimum square footage
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required cubic feet per BTU
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ventilation openings
Tony checks:
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louver sizes
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venting openings
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door undercuts
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mechanical room clearance
✔ 95%+ Furnaces
Use sealed combustion with PVC intake.
This draws air from outdoors, improving:
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safety
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efficiency
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humidity control
This design also means no interaction between indoor air and burner flame.
[Combustion Air Sizing & Mechanical Room Ventilation Guidelines]
5. Condensate Drainage: The Most Overlooked (But Critical) Part of High-Efficiency Venting
Condensing furnaces extract so much heat that water forms inside the secondary heat exchanger. This condensate must be drained properly.
Proper Drainage System Must Include:
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trap (required to prevent flue gas escape)
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proper slope (¼” per foot minimum)
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clean-out port
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condensate pump (if gravity won’t work)
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neutralizer kit (Tony installs these in most homes)
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freeze protection (in cold climates)
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insulated drain line
If the drain clogs:
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furnace shuts down
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water leaks occur
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heat exchanger rusts
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electronics can short
Tony never leaves a job without testing the drain for full flow.
[Condensing Furnace Drainage, Neutralization & Freeze Protection Manual]
6. PVC Vent Sizing: Bigger Is NOT Always Better
Most homeowners assume thicker or larger pipe = safer.
Wrong.
Tony sizes PVC based on:
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total vent length
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number of elbows
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furnace BTU input
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manufacturer vent charts
Oversized pipe can KILL furnace performance by reducing exhaust velocity.
Undersized pipe causes:
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restricted venting
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pressure switch failures
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ignition lockouts
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furnace cycling off under load
Correct sizing is mandatory.
7. Vent Termination Rules: The Mistakes Tony Fixes Most Often
Tony sees improper terminations constantly.
A correct exhaust termination MUST:
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extend the correct distance from the house
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face away from windows/doors
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rise above snow line
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maintain minimum clearance from grade
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have proper spacing between intake & exhaust
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avoid directing exhaust toward walkways
Wrong termination leads to:
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moisture damage
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frozen pipes
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gases re-entering the home
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furnace lockouts
These mistakes come from rushed installations — not codes.
8. Venting & R-32 Furnace Lineups: What’s Actually Different?
Even though R-32 doesn’t enter the furnace venting system, the furnaces built for R-32-era systems often include:
✔ Better sealed combustion chambers
✔ Improved condensate routing
✔ More corrosion-resistant materials
✔ Higher static-rated blowers (for thicker coils)
✔ Updated vent tables
✔ More efficient burner technology
✔ Improved pressure switch logic
These upgrades make the furnace:
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quieter
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more efficient
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safer
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easier to maintain
But the venting rules remain AFUE-based, not refrigerant-based.
[Modern Furnace Venting & Condensing Exhaust Engineering Reference]
9. Code Requirements Homeowners Don’t Know Exist
Tony always follows local and national mechanical code.
Most homeowners don’t know what’s required:
✔ No sharing vent with water heaters (in many condensing setups)
✔ Proper combustion air volume
✔ Minimum distances from doors, windows & meters
✔ Proper vent slope
✔ PVC primer color restrictions (some areas)
✔ Neutralizing condensate before discharge
✔ Fire-stopping penetrations
✔ Dedicated intake for sealed combustion
Failure to meet code = failed inspection + unsafe furnace.
[Residential Gas Appliance Venting & Mechanical Code Reference]
10. Tony’s Real-World Checklist Before He Fires Up a Furnace
Before Tony turns the furnace on for the first time, he verifies:
✔ vent slope
✔ no sags in PVC
✔ no joints without primer
✔ combustion air intake clear
✔ drain trap full
✔ condensate line flowing freely
✔ pressure switch operation
✔ exhaust pipe sealed
✔ termination location correct
✔ correct vent size
✔ neutralizer installed
Then — and ONLY then — does he fire up the furnace and check:
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flame behavior
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CO output
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draft pressure
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blower ramp
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temperature rise
This is where 90% of installers rush and skip steps.
Tony does not.
Tony’s Final Verdict: R-32 Doesn’t Change Venting — Efficiency Does
Here’s the truth:
✔ R-32 does NOT affect furnace venting
✔ AFUE determines venting (metal vs PVC)
✔ Combustion air must meet code
✔ Condensate systems must be installed correctly
✔ PVC venting MUST match manufacturer specs
✔ Neutralizers protect plumbing
✔ Proper venting = safe, efficient, quiet heat
If your installer talks more about refrigerant than about vent slope, pipe size, or combustion air?
Call someone else.
A furnace is a fire-producing appliance — it must be vented with precision.
That’s Tony’s way.
Now, Tony will tell us if this unit can be paired with any AC in the next blog.
