A proper vent with insulation baffle looks more like this: Insulation baffle around a B-Vent pipe in an attic Do not use com-mon vent systems. Diedrich Manufacturing, Inc. recommends UL certified (CE for European Union) Class-A Positive Pressure Ducting due to its superiority over the Single Wall welded seam 18-gauge ducting. 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. Inspecting HVAC Systems. Does Type B Gas Vent have a fire rating? When installed as a Type B Gas Vent, a minimum of one (1) inch airspace clearance to combustible material is required. But then I already knew that. For Type B 2x4 and BW Vents see Section 2, page 10 for clearance to combustibles. Furnace B-vent clearance from window. Here’s a guide: Table of Type B-Vent Rooftop Clearance Requirements. Metal vents that are too close to wood or combustionable materials may cause the wood to burst into flames. A B-vent is the metal duct that is normally used to vent gas and propane appliances such as furnaces and water heaters. The B vent is on the lower roof, 3 feet away and at least 2 feet below the other roof. Therefore, insulation, including fiberglass, should be a couple inches away from a B-vent to eliminate the hazard of a fire. 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. I know about the 1 inch rule. Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows: Durability is the result of high-quality materials and workmanship, with galvanized outer pipe and aluminum inner pipe providing protection against corrosion and external damage. This is an area where I slide on the requirements - I don't report on it. All locking joints are to be securely snap-locked together. vent system. ... B vent clearance; If this is your first visit, be sure to check out the FAQ. They are: 1. flue-gas temperature 2. heat loss in the vent 3. vent height 4. vent system capacity 5. restrictions to flow and 6. the ambient temperature. Type B Gas Vent requires a minimum of one-inch clearance to combustibles. NOTICE: Read these instruc- The manufacture even stamps this into the vent. Type B Gas Vent is designed for negative pressure applications and flue gas temperatures not exceeding 400°F above ambient for Category I appliances. Clearance Requirements from Vent Terminations to Building Openings for SV Models * All clearance requirements are in accordance with ANSI Z21.10.3 and the National Fuel Gas Code, ANSI Z223.1 and in Canada, in accordance with NSCNGPIC. WARNING: Vent pipe air space clearances to combus-tibles are 1"4000 on all sides except on the horizontal sections , which require 2" clearances from the top of the pipe. Single wall vents should have a minimum of 6 inches of clearance and double wall, sometimes called a “B” vent, should have 1 inch minimum clearance. The problem with this is that the single wall pipe requires even greater clearances (6″). The minimum requirements for vent ducting are: Single wall, welded seam 18 gauge ducting or Class-A Double Wall Positive Pressure Grease Vent Ducting. Where the termination cap penetrates a combustible wall, 1" air space clearance is required. jfrederick (Joshua Frederick) ... B-vents within 8 feet of a vertical wall are required to extend above the next roof line. Furnace vent pipe too close to combustibles. The 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer’s instructions. Factors Affecting Vent System Design and Operation There are many variables dictating how well a vent system will operate. These vents can achieve temperatures of 300 degrees when gas appliances are operating. In 16 years I have never seen a resulting problem of B-vent … Specific Inspection Topics. The B vent is in contact with the loose fill insulation. Type B Gas Vent requires a minimum of one-inch clearance to combustibles.