Reuben Saltzman

Flexible vent connectors

Every once in a while, we run across flexible vent connectors on water heaters or furnaces. They basically look like a flexible dryer duct, and there’s no way this could be a proper installation.

Flex vent connector 2

But they’re actually just fine.

Vent Connectors

Before I dig into this, I need to define exactly what I’m talking about. A gas vent is the vertical thing that takes exhaust gas up and out of the house. Or if we want to use the Fuel Gas Code definition, we’d say “A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance.” The vent is sometimes called a flue, a flue pipe, a flue vent, or a vent pipe, but the most accurate term is simply a vent.

A vent connector is what takes the exhaust gases from an appliance like a water heater or furnace and connects it to the vent. As the name clearly implies. The International Fuel Gas Code definition is “The pipe that connects an appliance to a chimney or vent.”  I’m being picky about this distinction, though, because the rules for vents and vent connectors are not the same. As a home inspector, I need to know the difference.

Flexible vent connectors

Flexible vent connectors are designed to take the place of rigid piping to make installations easier. They’ll have a B-vent type of transition piece at both ends, and this fitting should not be removed.

Flexible vent connector

You’ll also find a data tag on one of these ends, telling you it’s a listed product, and it’ll probably have some installation warnings on it.

Vent connector label

As a home inspector, I check to make sure the ends are still in place, and I make sure the entire run pitches upwards at a minimum of 1/4″ per foot. Runs should be made as straight and smooth as possible, with no bends greater than 90°. Flexible vent connectors also shouldn’t pass through floors, walls, or concealed spaces.

While this material looks very similar to corrugated dryer ducts, it’s much stiffer. It’s also much more expensive; the Home Depot by my house sells a 3′ section for $68. It’s no wonder these things aren’t more popular.


While they’re not common, flexible vent connectors are fine to use, provided they’re installed in accordance with the manufacturer’s instructions.

Related Post: Inspecting a water heater vent connector

One response to “Flexible vent connectors”

  1. Michael Bronner
    June 21, 2022, 1:32 pm

    Reuben, you’re great at this. Why don’t you do a piece on vent off sets, definition, where used and the rules?

RSS feed for comments on this post.

Comments on posts over 90 days old are disabled, as of 1/7/14.