6 3-Inch Double Wall Water Heater Exhaust Pipe of 2026 For Safe Flues

1

Mineye 3.15'' Stainless Steel Vent Wall Thimble for Gas Tankless

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  7.6
• Brand
  Mineye

Key specs2

Wall Thickness Range

4.7 in to 7.8 in adjustable length

Collar Inner Diameter

3.15 inches for tankless venting

Pros & cons32

Pros

• Telescoping sleeve adjusts from 4.7 inches to 7.8 inches to fit varying exterior wall thicknesses
• Stainless steel build resists corrosion and helps maintain outer wall cooling during horizontal venting
• Wide 9.84-inch square flashing plate provides broad coverage across wall cutouts

Cons

• Sized at 3.15-inch inner diameter, so it does not fit standard 3-inch Type B round pipe without an adapter
• Designed strictly for horizontal wall pass-throughs rather than vertical roof penetrations

2

DuraVent 3GV06 3" Inner Diameter - Type B Round Gas

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  8.9
• Brand
  DuraVent

Key specs2

Section Length

6 inches

Joint Compatibility

Connects directly with DuraVent Type B gas vent components to maintain a secure locking seal.

Pros & cons32

Pros

• Short 6-inch pipe length allows precise clearance adjustments in tight vertical flue runs
• Standard 3-inch inner diameter matches standard Type B gas vent water heater draft hoods
• Aluminum double-wall construction provides inner flue insulation for natural draft appliances

Cons

• DuraVent locking joints require matching DuraVent fittings rather than third-party pipe brands
• Six-inch section adds minimal overall run length, requiring multiple pieces for long spans

3

Duravent® 3gv60 Round Type B Gas Vent Insulation Pipe, 3"

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  9.7
• Brand
  DuraVent

Key specs2

Flue Section Length

5 feet (60 inches)

System Assembly

Spans longer runs with fewer joint connections, reducing potential draft leakage points along the vertical run.

Pros & cons32

Pros

• Five-foot section length spans tall vertical rises with fewer joints to assemble and inspect
• Double-wall Type B insulation design maintains draft temperature inside the flue
• Standard 3-inch round profile fits common residential Category I gas water heater installations

Cons

• Requires matching DuraVent Type B pipe to maintain a secure locking joint without air gaps
• Long 60-inch rigid section is awkward to maneuver in cramped utility closets or low basements

4

Selkirk 3 in. Dia. x 60 in. L Aluminum Round

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  8.3
• Brand
  Selkirk

Key specs2

Wall Construction

• Aluminum inner wall promotes fast warm-up
• Galvanized outer wall protects against framing contact

Assembled Diameter

3 inch inner diameter Type B

Pros & cons32

Pros

• Aluminum inner wall paired with a galvanized steel outer wall provides sturdy thermal shielding
• Full 60-inch length minimizes the number of connections needed across tall ceiling spaces
• Type B design supports standard Category I natural draft gas appliance venting

Cons

• Proprietary Selkirk lock system does not lock securely into DuraVent or AmeriVent pipe sections
• Rigid 5-foot length requires accurate vertical measuring to avoid awkward cut requirements

5

3" X 60" GAS VENT PIPE 3E5

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  8.1
• Brand
  AmeriVent

Key specs2

Pipe Weight

4.71 lbs for manageable overhead handling

Connection Check

Verify matching AmeriVent fittings across the entire exhaust run to maintain airtight snap-lock connections.

Pros & cons32

Pros

• Five-foot span reduces joint counts on straight vertical water heater exhaust runs
• Lightweight 4.71-pound construction simplifies positioning and overhead pipe hanging
• Standard 3-inch diameter matches Category I natural draft gas appliance vent collars

Cons

• AmeriVent locking profile is not compatible with other brands without specialized adapters
• Listing does not specify wall gauge or inner alloy specs, requiring manufacturer verification

6

Metal-Fab 3M18 Double Wall Vent Pipe 3 in. x 18

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  7.6
• Brand
  Metal-Fab

Last update on 2026-10-27 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

Do different brands of 3-inch double-wall vent pipe lock together?

No, you should never expect different vent pipe brands to snap together tightly. Locking joints and connection seams are brand-specific, meaning sections from DuraVent, Selkirk, and Metal-Fab use different mechanical tolerances. Mixing brands can leave loose gaps that leak combustion exhaust into living areas or framed chases. To maintain a secure, draft-tight flue run, choose one manufacturer line for all your 3-inch elbows and straight pipe sections.

What is the difference between a 3-inch Type B gas vent and a 3.15-inch vent pipe?

A standard 3-inch Type B gas vent features a 3.0-inch inner diameter, whereas a 3.15-inch pipe is designed around metric dimensions commonly found on gas tankless water heater collars. For example, the Mineye double-wall wall thimble uses a 3.15-inch inner diameter tailored for horizontal tankless exhaust runs. Forcing a standard 3-inch pipe onto a 3.15-inch collar will distort the connection and compromise the seal. Always verify the water heater collar diameter in the manufacturer manual before choosing your flue pipe.

Do I need a wall thimble for horizontal water heater venting?

Yes, routing horizontal water heater exhaust through an exterior wall requires a dedicated pass-through sleeve like a wall thimble. A wall thimble insulates combustible framing materials from the heated pipe as it passes through the building envelope. Components such as the Mineye stainless steel wall thimble feature a retractable length from 4.7 inches to 7.8 inches to adjust to various wall thicknesses. Check your appliance manual to confirm the exact wall opening dimensions and sleeve depth your installation demands.

What clearance is required around 3-inch Type B gas vent pipe?

Required clearances to combustible framing depend entirely on the specific manufacturer listing and local building codes. Type B round gas vent pipe, such as aluminum double-wall sections from Selkirk or DuraVent, uses an internal air space between walls to reduce exterior heat transfer. Because minimum clearance distances vary depending on whether the pipe is enclosed or open, check the safety label stamped directly on the outer galvanized pipe casing before building any framed enclosures. If venting through walls presents structural challenges in your space, evaluating alternatives to gas heaters can help identify options that avoid exterior flue runs altogether.

Can 3-inch double-wall gas vent pipe be cut to length?

No, standard double-wall Type B vent pipe sections cannot be cut shorter in the field. Cutting the pipe destroys the factory locking seams and separates the inner aluminum liner from the outer wall. Flue runs are assembled by combining pre-measured factory sections, such as 6-inch pieces like DuraVent 3GV06, 18-inch sections like Metal-Fab 3M18, or 60-inch lengths like the Selkirk gas vent pipe. If your run requires an intermediate length, look for an adjustable slip section engineered specifically for that manufacturer product line.

How do I confirm my 3-inch exhaust connections are secure?

You can confirm a secure connection by visually checking that the locking tabs or snap seams fully engage around the entire circumference of the joint. When straight sections such as 60-inch round Type B pipes connect, the male and female ends must seat completely without twisting or wobbling. Vertical runs must be supported according to manufacturer guidelines so the weight of upper pipes does not place downward pressure on the heater draft hood. If you are debating between maintaining a vented gas water heater system or converting to cleaner utilities, consider the advantages of electric heaters over fossil fuels when planning long-term household upgrades.