Never saw this type of flue cap before. This was a brand new home and it had 2 of these. They were single wall design, each about 3' long. The flues were proper B vent types until they entered these roof caps. The B vent only extended about 1 foot into the roof sections. They were not otherwise attached or sealed, and there was a gap around it between the top of the B vent and the inside wall of the cap. My concern is that condensation may occur on the single wall part above the termination of the B vent. It would then rain down back into the attic.

I read the furnace installation instructions on site which only said to use a "manufactured" flue and roof cap rated for the purpose.

Anyone know if these are OK?

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