DuraVent 5GVIS Type B 5-6 Diameter Attic Insulation Shield. Required for installations that pass through an attic to prevent insulation and debris from accumulating near the vent. Cylindrical section adjusts from 11″ to 20″. Inside diameter of cylindrical section is 8-3/4 inches. Outsie diameter of cylindrical section is 8-15/16 inches. Base Plate is 11 inches square. A product from DuraVent’s Type B Gas Vent system. Use with natural gas or liquid propane category I and drafthood equipped appliances, and appliances tested and listed to use Type B Gas Vent. Applications include: natural gas fireplaces, gas-fired furnaces, boilers, water heaters, and wall or space heating applications. Type B Gas Vent has been engineered to heat up rapidly. It remains hot during the operation of the appliance with minimal condensation on the appliance and vent system. To view our full line of products! We can not hold or reserve this item. This is calculated at checkout. PLEASE NOTE: All HVAC equipment should be installed by a licensed professional. Return costs are your responsibility. If the box has any damage, or if there is any reason for you to be at all concerned about damage, please write “PRODUCT DAMAGED” clearly on the sheet that they ask you to sign. Once you sign for the package you accept full responsibility. Even if you do not intend to install your merchandise right away, please be sure to check and make sure it arrived intact otherwise the claim will be up to you and we will not be responsible for the damage. We will do everything in our power to fix the problem incurred by damage, but please be aware that it is your full responsibility to inspect all goods before signing for them.