Natural Gas clothes dryer

I’m looking for the recommended vent pipe for a natural gas clothes dryer. I didn’t find any information in any of the classes I have taken.
I have seen the flexible metal Home Depot type vent pipes but have heard that a rigid PVC 4" pipe is required to avoid collection of flammable lint etc. Can anyone shed some light on this subject for me please? Thanks

Here are the basics:
Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.4 mm) rigid metal ducts, having smooth interior surfaces, with joints running in the direction of air flow. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct.

This means that the flexible, ribbed vents used in the past should no longer be used. They should be noted as a potential fire hazard if observed during an inspection.

The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7,620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.8 rad) bend, and 5 feet (1,524 mm) for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.
This means that vents should also be as straight as possible and cannot be longer than 25 feet. Any 90-degree turns in the vent reduce this 25-foot number by 5 feet, since these turns restrict airflow.

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PVC pipe is not suitable for dryer exhaust…

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Thanks Brian I appreciate the help.

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whoever you heard that from don’t listen to them anymore

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:rofl:

PVC piping can allow static build up. This static charge may ignite dryer lint leading to spontaneous combustion.

Food for thought: Coin Laundromat Fires.
Cotton, which is combustible, starts to decompose when the surface temperature reaches approximately 205°F, and in the process generates its own heat. For a point of reference, the normal “High Temperature” setting on a dryer is 190°F. This decaying process is accelerated when the fabric is tightly folded and placed in a confined area (like when someone over stuffs a dryer). Because it is hot, moist, and has no possible way to dissipate its heat, the oxidation continues to build upon itself, until the garment reaches the critical surface temperature and bursts into flames.

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Hadn’t thought about the static build up. Thanks

Brian, the flexible transition duct can be used to connect the dryer to the exhaust system as long as it’s not conceded in the wall - right?

dryer-exhaust

According to this page on the Residential Plumbing Overview for Inspectors Course:

The maximum length of a clothes dryer exhaust duct should not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length is reduced by 2-1/2 feet for each 45-degree bend, and 5 feet for each 90-degree bend. The maximum length does not include the transition duct.

Like most things, I think we all need to see what the local jurisdiction has to say.

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You’re right. It has been changed.

This is one is updated

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Correct, 8’ foot max, no splices, no concealed connections.

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