Code 8.15.3 & 8.15.4

[Samjohn]

Hello,

Code 8.15.3 & 8.15.4

Question- an appliance that requires C or B venting (ie hot water tank or a commercial unit heat located indoors)

Does the B vent need to be within 16" of the appliance draft hood or flue outlet?

I occasionally see commercial hot water heaters with many feet of C vent and then transition to B vent before existing the roof of the building.
Am I interpreting these codes correctly?

[Admin]

Clause 8.15.4 mentions using a max 18" C-vent connector when the required vent is listed as B-vent.

There are still appliances that allow the use of C-vent for the vent connector that connects into a B-vent chimney, if the appliance BTU's fall within the MIN and MAX listed in Tables C2 and C4.

Most unit heaters now require all horizontal venting to be stainless steel.

It depends on what the appliance installation manual approves.

8.15.3
A vent may be directly connected to the flue outlet or draft-hood outlet of the appliance that it serves, provided that the vent is independently supported and the connection is made in accordance with the manufacturer's instructions.

8.15.4
When the vent referred to in Clause 8.15.3 is of double-wall construction, the connection shall be made by the use of a certified double-wall to single-wall adapter, and by
a) an adjustable telescopic-type fitting, fabricated by the vent manufacturer; or
b) a single-wall vent connector having a maximum length not exceeding 18 in (450 mm) and a minimum length not less than 12 in (300 mm).