Exhaust adapter, exhaust structure for water heater, and method for installing exhaust adapter

An exhaust structure for water heater, comprising:

• a water heater;
• an exhaust tube which has one end and the other end and is connected to said water heater at said one end;
• an exhaust pipe into which a part of said exhaust tube at the other end thereof is inserted;
• and
• an exhaust adapter which is formed to have an annular shape enclosing a through hole, and is mounted on an outer peripheral surface of said exhaust tube by inserting said exhaust tube into said through hole and is mounted on an inner peripheral surface of said exhaust pipe,
• when said exhaust adapter being fitted on said outer peripheral surface of said exhaust tube, an inner peripheral surface of said exhaust adapter pressing said outer peripheral surface of said exhaust tube, and when said exhaust adapter being fitted on said inner peripheral surface of said exhaust pipe, an outer peripheral surface of said exhaust adapter pressing said inner peripheral surface of said exhaust pipe, wherein
• said exhaust adapter includes
• a first annular member having an inner peripheral wall and an outer peripheral wall and located innermost said annular shape;
• a second annular member having an inner peripheral wall and an outer peripheral wall and located outermost said annular shape;
• and
• a third annular member having an inner peripheral wall and an outer peripheral wall and located between said first annular member and said second annular member and having a hardness higher than any of said first annular member and said second annular member,
• the first annular member, the second annular member, and the third annular member are arranged concentrically and enclose the through hole,
• the exhaust adapter is made of an elastic material,
• the first, third, and second annular members compose a three-layer structure,
• the first annular member is made of a different material from the second annular member, and
• the first, third, and second annular members are arranged concentrically such that the inner peripheral wall of the second annular member is positioned in height and radius radially outward from the inner peripheral wall of the third annular member.