Crossbreak:

Crossbreak: Diagonal bends made in metal panels to
increase rigidity and decrease flexibility.
Debris: Non-adhered substances not intended to be
present within the HVAC system.
DOP Testing: The percentage removal of 0.3 micrometer
particles of dioctylphthalate (DOP) or equivalent used to
rate high-efficiency air filters, those with efficiencies
above 98%.
Double Wall Duct: Sheet metal duct usually constructed
with an inner perforated liner sandwiching fibrous glass
insulation.
Duct Access Door: Fabricated metal barrier (hatch) by
which a service opening is accessed or closed.
Designed for permanent installation. May be available
pre-fabricated in a variety of sizes and configurations.
Most utilize cam locks for securing the removable door
from the permanently installed doorframe. Types of
Duct Access Doors are listed below: