Flexible Dryer Vent Transition

[Admin]

Some people assume you can't use a flexible duct to connect a gas dryer to a rigid dryer vent.  An appliance technician told me the TSSA told him so, but he must have misunderstood because there is no such Code to prevent the use of a flexible duct on both residential or commercial clothes dryers.

The Ontario Building Code Article 6.2.3.2(4) says,

Duct connectors that contain combustible materials and that are used between ducts and air outlet units shall,
(a) conform to the appropriate requirements for Class 1 air duct materials in CAN/ULC-S110, "Test for Air Ducts",

The B149.1-15 Gas Code Clause 7.5.1 says,

Clause 7.5.1 - A dryer shall be equipped with a moisture-exhaust duct that terminates outside the building, and the duct shall be constructed of a material that is
(a) noncombustible; or
(b) certified as meeting the requirements for Class 1 air ducts contained in CAN/ULC-S110.

See the first attachment from Ecco supply who sell both the foil and vinyl type flex.

Some dryer manuals may say you can't use foil flex.  In which case we don't as per Clause 4.1.3 & 4.1.4 of the B149.1-15 Gas Code,

Clause 4.1.3 - An appliance, accessory, component, equipment, or any other item shall be installed in accordance with the manufacturer's certified instructions and this Code.

Clause 4.1.4 - Where a conflict exists between the manufacturer's certified installation instructions and this Code, the most stringent of the two shall prevail.

Here's an example of a dryer vent manual that says you can't but then says you can if rigid cannot be used.

DO NOT install a clothes dryer with flexible plastic venting materials. If flexible metal (semi-rigid or foil-type) duct is installed, it must be UL-listed and installed in accordance with the instructions found in "Connecting the Dryer to House Vent" later in this manual. Flexible vent materials are known to collapse, be easily crushed and trap lint. These conditions will obstruct dryer airflow and increase the risk of fire.

UL-LISTED FLEXIBLE METAL CLOTHES DRYER TRANSITION DUCT
If rigid metal cannot be used, then UL-LISTED flexible metal clothes dryer transition duct (GE parts - PM08X10085, WX08X10085 or WX08X10077) can be used.

With Commercial-type clothes dryers we follow Clause 7.4.3,

Clause 7.4.3 - A certified flexible foil noncombustible-type duct may be used as a transition connection between the dryer exhaust and a rigid moisture duct.

You would then have to use noncombustible flex as shown in the second attachment.

I'm not sure why Clause 7.4.3 references flexible foil duct because as far as I know foil flex duct is combustible.  This Clause should be amended and remove the word foil.

[Porcupinepuffer]

I agree. any foil type flex I've ever seen could easily burn through with a lighter in a matter of seconds. Never seen a brand of it that was noncombustible.