A Type B Gas Vent, often called “B-Vent” or “double-wall gas vent,” is a commonly used venting system for Category I gas appliances (furnaces, boilers, water heaters) operating at moderate flue temperatures. Hart & Cooley’s Type B Gas Vent system features:
A double-wall construction: inner liner (usually aluminum or corrosion-resistant metal) and outer galvanized steel shell, with an air space in between for insulation and cooling.
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Locking joints or snap-lock / locking band couplings to secure segments and resist separation under vibration.
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Designed for negative pressure (draft) applications and to handle flue gas temperatures not exceeding about 400 °F above ambient (i.e. limited heat design).
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Meets UL 441 standard for listed gas vent systems.
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Widely used in residential and light commercial venting for gas appliances, often in vertical runs, with accessories like elbows, tees, supports, caps, etc.
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In practical installation, you’d use a 24" (2 ft) pipe segment as part of a run, connecting to other segments or fittings until reaching termination.