Special Gas Vent

Our technical support personnel have identified the following questions about gas venting as the ones most frequently asked. The answers are designed to help you better understand the nature of this type of vent, but we recommend that you consult the installation instructions for the manufacturer of your vent, the listing by Underwriters Laboratories and your own local building codes.

What is a Type "B" Gas Vent?
Type B Vent is an Underwriters Laboratories' designation for product tested under the UL 441 Testing Standard. It's a type of two-wall, air insulated, venting system that is used for gas burning appliances and is tested and listed by UL for safety.

What is the maximum venting temperature for Type B?
Type B Gas Vent is not rated for a specific temperature level, but this type of product should only be used on gas-fired equipment that has a draft hood or that was tested and listed for use with Type B Gas Vent systems. This type of equipment, such as furnaces, heaters, and water heaters, typically has an outlet temperature in the 400º F plus room temperature range. However, even if the temperature is correct, the instructions for the equipment should be checked to make sure it was tested for use with Type B Gas Vent.

Is it difficult to put Type B sections together?
There are a number of connecting methods used by gas vent manufacturers. We believe that the AmeriVent® Type B Gas Vent system, manufactured by American Metal Products, is the easiest vent to assemble on the market today. The patented snap-lock locking system allows assembly by just pushing the sections together until you hear a 'click.' There are no male and female openings to line up or locking brackets to worry about-just push and snap the sections together.

Can the sections come apart when I don't want them to?
Sometimes, vent systems with a twist-lock or the type of lock requiring a locking band can come apart when putting a flashing on the roof or when you are adjusting an elbow. Be assured, AmeriVent®'s snap-locking system will not come apart unless you want it to. There's no need to worry about the possibility that when you are working on one part of the AmeriVent® system that you might unlock a section somewhere else.

Once the locking ends are joined together, isn't it difficult to take them apart?
Not at all. The lock at the bottom end of each AmeriVent® section has three locking teeth marked with an embossed dot. Simply pry out the three locking teeth and twist the sections. They come apart easily. To reuse the section, push the teeth back in, and it's ready to install.

Can I install drywall or wall board right up against the gas vent?
No. Drywall and wallboard are considered combustible materials and should not be installed against the vent including the use of this material to close off the hole around the vent. Type B Gas Vent requires a minimum of one-inch clearance to combustibles. This one-inch is a typical clearance for all brands of Type B Vent, but each section of vent pipe is marked with the clearance required by Underwriter Laboratories, so it should be checked.

Does Type B Gas Vent have a fire rating?
No. Because the Type B Gas Vent system is tested and listed by Underwriters Laboratories for safety, it doesn't need a fire rating. The material for the outside wall is the same as that required for a firestop.

Can I use Type B for an oil burning furnace or water heater or on a fireplace or stove?
No. Type B Gas Vent can only be used on gas fired equipment-either natural gas or LP gas.

How do I support the AmeriVent® pipe sections?
AmeriVent® Type B Gas Vent Systems can be supported by two of the easiest to use support systems in the industry today: 1-The Ameri-Bucket Support or 2-The Firestop Support Plate Assembly-both of which are Underwriters Laboratories listed. In addition, field-fabricated supports may be used. Consult your local building codes for applicable regulations regarding field-fabricated supports.

How long will the AmeriVent® Type B vent last?
AmeriVent® components are made from materials unsurpassed in the gas vent industry and should last as long as the heating system in your home. The inner wall is made from a highly corrosion resistant aluminum alloy and the outer wall is made of a hot dipped galvanized steel that meets or exceeds all UL requirements.

How far above the roof does the vent pipe need to extend?
With the patented AmeriVent® Ameri-Cap, the system can be installed on most roofs with an outlet at a minimum of one foot above the roof. It is important that the installer read the Termination Section of the Installation Instructions and the local building codes to check for exceptions.

Will strong winds blow the Ameri-Cap off the vent?
No! Because the AmeriVent® snap-lock locking system cannot be accidentally unlocked, unlike other types of cap locks, the Ameri-Cap will never blow off in strong winds.

In the AmeriVent® system, will the air in between the two walls rise up and create heat loss and condensation problems?
No, the two walls are spot welded together at the top of each section, and therefore, the air inside cannot rise because the space is dead air space.

Is there a correct 'up and down' direction for installing AmeriVent® components?
Yes. There is a correct direction, and each section is marked with an 'up' arrow that shows the proper orientation, or direction of the section, which is always away from the appliance.

How many elbows or offsets can be used in a vent system?
The rules may vary from area to area, and you should always check with the local building inspector. With the appliances used today, the use of an excessive number of elbows can cause condensation problems. Try to limit the installation to no more than two 90º offsets and to use offsets of no more than 45º wherever possible.

Do elbows require special supports?
A Type B Gas Vent elbow is not designed to carry any load, therefore, whenever an elbow or offset is used, it must be resupported.

When and where should firestops be used?
First, a metal firestop must be used at each floor level that the vent passes through, with the exception of the roof level where no firestop is required. Secondly, the firestop should always be located at the bottom surface of each floor level except for the upper floor where the firestop should be installed on top of the joist areas in the attic.

What gauge metal is the AmeriVent® Roof Flashing?
AmeriVent® Flashings are made from .018 inch, 26 gauge, G90 galvanized steel, as are the firestops and the outer wall of the vent sections.

Are sheet metal screws required for the AmeriVent® system?
No. It is not necessary to use screws with the AmeriVent®'s snap-lock connecting joints. Unlike other locking methods, the snap-lock joint is designed to come apart only when you want it to and not accidentally. Screws can cause problems with the joints and vent, and your inspector will probably red tag your system if you use them.

Can Type B Vent be wrapped with insulation to keep it warm?
No. The vent requires a minimum of one-inch clearance to all combustible material. For severe problems such as cold attics, contact the Technical Services Department of the manufacturer for alternative solutions.

Note:
This is not intended to take the place of the factory furnished installation instructions.
For more information on AmeriVent® gas venting and other air distribution products, call the Technical Services Department of American Metal Products, (800) 669-3190.