Appears to be flexible liner used as a vent connector, for which it is not approved or listed. There are listed flex connectors, which are heavier, stiff and carry listing lablels. This appears to be liner adapted with single walled pipe into B-vent above and below. No draft hood connector, lack of proper support, oversized liner. Cannot use single walled connector in attics regardless if flex or rigid.

I recommend the entire run be done by a qualified HVAC tech using the same brand of B-vent installed to the listing. Then, have him inspect the unit and test it for proper setup.

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disgusted with some people on this forum. Out of here!