Home inspector cited the following as a code violation saying the wye pipe for the furnace and water heater is too close to the header above a pair of bifold doors. Said the single wall pipe should be replace with double wall.

Here are some pics. House is 13 years old and has a 2 year old Bryant 80% unit and new Rudd water heater. Basement was finished sometime after the house was originally built.

Can I simply go to Home Depot and pick up a double wall wye pipe? Does this have to be a B Vent?