AskCodeMan

Jerry,
what are the clearances and other relevent specs for the flexible vent material. I assume it's the same as single wall?
I do notice however, it's always at a negitive slope at some point in its run.

Hi Marc,

That flexible vent material is made in two versions: single wall and double wall Type B gas vent.

The single wall flexible vent is like the single wall vent - it requires 6 inches clearance to combustible material and to insulation, and it is not allowed in the same locations which single wall is not allowed.

Likewise, the double wall flexible Type B gas vent requires 1 inch clearance to combustible material, however, unlike rigid Type B gas vent, the flexible type is not (to my knowledge) allowed to run through walls, ceilings, concealed spaces and the like as this is not actual "vent" but is a "vent connector".

You are correct, if the flexible material is run horizontally (sloped 1/4" per foot minimum) then it usually also has negative slope sections, which is not allowed.

Also note that the tape used is not allowed to be used.

Plus, the water heater vent looks flattened out facing the viewer.

Is the larger flexible (vent?)(duct?) an appliance vent or a dryer duct?

Here is an example of a double wall flexible vent *connector* installation instructions: http://www.hartandcooley.com/vent/instr ... ctions.pdf

Here is an example of single wall flexible vent *connector* installation instructions (note that this has a 1 inch clearance to combustible material): http://www.americanmetalproducts.com/ve ... l/flex.pdf

Thanks Jerry.
The larger is a FAU vent. I thought there may be some speak of this material in the IRC or CMC, however I found nothing.
What say you? you think it's too new of a material?

Marc,

Marc M wrote:I thought there may be some speak of this material in the IRC or CMC, however I found nothing.

The IRC and IMC does address those connectors in this way:
- From the 2006 IRC. (bold and underlining is mine)
- - M1803.1 General. Connectors shall be used to connect fuel-burning appliances to a vertical chimney or vent except where the chimney or vent is attached directly to the appliance.
- - - M1803.3 Installation. Vent and chimney connectors shall be installed in accordance with the manufacturer’s installation instructions and within the space where the appliance is located. Appliances shall be located as close as practical to the vent or chimney. Connectors shall be as short and straight as possible and installed with a slope of not less than 1/4 inch (6 mm) rise per foot of run. Connectors shall be securely supported and joints shall be fastened with sheet metal screws or rivets. Devices that obstruct the flow of flue gases shall not be installed in a connector unless listed and labeled or approved for such installations.

From the 2007 CMC:
- Table 8-2
- - Clearance for Connectors
- - - Minimum Distance from Combustible Material
- - - - Equipment | Listed Type B Gas Vent Material
- - - - Listed equipment with draft hoods and equipment listed for use with Type B gas vents | As listed
(difficult to lay the table out here, but the "|" indicates column separation)

The 2007 CMC is not as easily worked through and followed as the 2006 IMC it was derived from, nonetheless, though, the 2007 CMC does address those listed connectors as having to be installed in accordance with their listing.

Very nice, thanks Jerry. My fault for not looking for "connector" as opposed to "Flex-vent" or something similiar.

Only listed flexible appliance connectors are recognized by the code. Unlisted flex connectors such as sections of flex chimney liner are not recognized. The big differences btw these are: being self-supporting, strong enough to resist blunt trauma and listed connections.

Regardless, you still must observe sizing requirements. For instance, most 40 K BTU/hr. DHW heaters with a 3" collar off the draft hood require a 4" diameter connector. However, with flex, you would probably need to use a 5" connector to allow for a 20% de-rating due to the flex. If a mfr. has tested their listd flex connector and the listing agency agrees it has a smooth wall sufficient to provide adequate flow at the stated diameter then no de-rating would apply.

On a personal note, most homemade flex connectors I find are undersized, smashed, and the seams are separating. The listed flex connectors on the other hand hold up very well and are very durable.

HTH,
Hearthman