L vent to single wall?

This oil-fired boiler vent reduces at the flue. Am I correct in saying that it transitions from a double walled L-vent to a single walled pipe (maintaining the interior diameter)? BTW - the label was no help.

vent conn reduces.JPG

Are you sure thats double wall L-Vent on the right? It looks like older single wall crimped into a reducer fitting.

Also there are special fittings to go from double to single wall, with one side an insert-and-twist for the double wall, and the other side insert-and-screw for the single wall.

I agree looks like that to me also … Roy

You are right Rob (and Roy) - it was a single wall. There were no twist and fit joints. Therefore - the reduction is improper, correct?

Correct… Roy

Thanks Roy.

Yes you not reduce a oil fired burner, At least 15 years ago you couldn’t lol