How to Cut Into HVAC Ductwork


An HVAC ductwork system consists of a plenum, a trunk line and several branch lines. The plenum routes the air to various ducts; the trunk line is the main conduit, usually larger than the branches. Duct installers tap branch lines into the trunk line and the trunk line taps into the plenum. Some larger HVAC systems have more than one trunk line. Certain types of ductwork requires access doors cut into or near its bottom. Duct installers use hand tools to cut the holes. To maintain maximum energy efficiency, doors and taps must fit tightly in the holes cut into the ductwork.

Things You'll Need

  • Marker
  • Flat-head screwdriver
  • Hammer
  • Red-handled tin snips
  • Lay out the duct's hole. Hold the duct tap or access door's dovetail tabs, the tabs that lock the fitting to the ductwork, against the ductwork and trace the tabs' outlines with a marker.

  • Hold the edge of a flat-head screwdriver's blade against one corner of the outline. Strike the screwdriver blade with a hammer. Create a 1-inch-long slice in the duct with the hammer and screwdriver. The slice must go from the corner of the outline toward its center.

  • Slip a red-handled tin snip blade into the left-hand side of the slice. Red-handled tin snips make right-handed and, with practice, straight cuts. The tin snip blade on the inside of the duct must always face the center of the hole.

  • Cut a hole from the middle of the slice to the outline with the red-handled tin snips. Once the tin snips reach the outline, turn the snip's blades so they face the line and extend the cut across the line to the corner of the outline. Do not remove the tin snips.

  • Turn the tin snips' handles so the blades face the next line.

  • Cut the second line with the red-handled tin snips until it reaches the next outline corner. The inside blade will force the cut section of duct out. To make cutting easier, pull on the cut section of duct with one hand while squeezing the tin snip's handles with the other hand.

  • Turn the tin snips blades toward the next line, then cut the line. Continue to pull on the cut section of duct. Repeat this procedure for the remaining line.

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