HVAC Drafting with AutoCAD – From Beginner to Pro!

A: Flow divided by velocity gives area: 1.2 / 6 = 0.20 m². A: 0.20 m² exactly, but ignores liner and flange loss — looks right but isn’t what you’d actually draft. B: 0.18 m², close enough once lining is added. C: Same area as B, but extreme aspect ratio raises pressure drop. D: Same trick again — velocity noise and fittings will kill you.

A: A: Too thin — surface temp will sit below dew point and sweat. Seen it fail. B: 25 mm typically pushes surface temp above room dew point in this delta-T. That’s why specs land here. C: Works thermally but overshoots the need and eats space; rarely justified at 7 °C. D: Paint doesn’t change surface temperature; condensation still forms.

A: A: Flex connectors exist mainly to break vibration paths. Missing it sends vibration everywhere. B: Structure-borne noise rides the same path. C: Thermal expansion of short duct runs isn’t what flex connectors are solving; wrong mechanism. D: Installers rely on that bit of give to line things up.

A: A: 80 kPa divided by 9.81 kPa/m ≈ 8.2 m. Clean conversion. B: Common slip — adding an unstated margin. C: That’s treating kPa like meters directly. Seen on bad submittals. D: Decimal shift error; happens when gravity gets dropped.

A: A: You can’t even get a hand in there. Unrealistic. B: Controls alone aren’t the issue; heaters and dampers need space. C: That range matches what techs need to pull actuators and heaters. D: Removable tiles don’t replace physical working space.

A: A: Without an actuator and wiring, the damper is just a blade. It won’t move on command. B: Normal airflow isn’t affected if it’s stuck open. C: Pressure drop comes from blade position, not missing wiring. D: That’s an electrical protection issue, not a damper one.

A: A: Too light — oil canning risk at this width. B: Borderline and often rejected by reviewers. C: 22 ga is the usual call once you pass about 750 mm. D: Structurally fine but overkill unless pressure class demands it.

A: A: Too coarse — clashes disappear. B: 1:100 balances readability and coordination for most floors. C: Detail scale, not GA. D: Shop-detail territory, not plans.

A: A: Load calcs don’t read CAD layers. B: Coordination tools filter by layer; the duct vanishes from clash runs. That’s a real pain later. C: Fan sizing comes from schedules, not layers. D: Inspectors care about install, not CAD layer names.