Rinnai 223176PP 12-Inch Condensing Horizontal Termination Kit Engineered especially for gas appliance venting Positive fit and lock allows for installation assurance Two layers of pipe equals two layers of protection Seals at every joint expand and contract with weather and temperature changes, so there's no flexing or cracking in the venting No flammable, messy or harmful glues, cements, or solvents are used