In order to better understand this article, take a minute to look closely at photos “A” and “B” below. Based on the photos, try and determine which metal vent is allowed to be installed in your gas appliance venting system. Venting is the process of distributing the poisonous combustion byproducts, such as Carbon Monoxide, to the exterior of the home.
Having trouble picking A or B?
You aren’t alone. The introduction of flexible gas venting materials has led to some confusion in the home inspection, and HVAC industries. During our routine Richmond home inspections, we often find flexible materials used in the venting system. Some are acceptable, and some are not. It is not always apparent by simply looking at the material, and nearly impossible to make a determination based on a photo. So what do you need to know about flexible vents?
Some flexible vents are not intended to be used for venting gas appliances. They may be used for dryer venting, bathroom or kitchen venting, or other purposes, but not gas appliances. The flexible vent in photo A is not approved for venting gas appliances. It’s intended purpose is for dryers.
Vents that are listed and approved as flexible B-vents for gas appliances can be installed where rigid B-Vents are allowed (with a few installation differences). The best way to determine this is by looking at the label. Flexible B-vents are listed and labeled as such .
Photo B is if a listed flexible B-vent. One of the biggest differences between photo A and B, is that B has two walls. You can’t see that in the photo, and since home inspections are non invasive, (we don’t take anything apart) its not a method applicable to an inspection. Whenever we see flexible vents installed on a gas appliance, we always check the label to ensure its approved for that purpose. Unlike rigid B-vents flexible B-vents can not be enclosed, and can not be installed through walls, floors or ceilings. Both flexible, and rigid B-vents require 1 inch clearance from combustibles such as drywall. For more detailed installation instructions click here Flexible B-Vent installation