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Video · HVAC Installation Craft

HVAC Plenum Up Close: Checking Seams and Sealing Around the Coil

An HVAC plenum is the sheet metal box that joins your equipment to the ductwork, and its seams leak if nobody seals them. This first-person clip shows a tech checking and sealing a plenum around the coil.

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What you’re seeing in this video

The camera rides on the tech's head, looking into an air handler cabinet and the plenum connected to it. A gloved hand runs along the sheet metal seams, feeling for gaps, while a work light sweeps into the corners.

Then the sealing starts. Foil tape goes over the joints and sealant fills the gaps around the evaporator coil, the indoor coil that cools the air. The goal is a box that only lets air out where the ducts are.

Job footageSwiftPro
Topic
HVAC Installation Craft
Length
0:27
Posted
August 27, 2026
Shot by
The SwiftPro crew, Northern Virginia

Why it matters in your house

  • Leaks at the plenum waste the most air because they sit right at the blower, where pressure is highest. Air escaping there never reaches a single room.
  • Uneven temperatures, weak airflow at the far rooms and a system that runs long can all trace back to an unsealed plenum.
  • With the fan running, hold your hand near the plenum seams. If you feel air or see light through a joint, that seam is leaking and worth fixing.

What is an HVAC plenum?

It's the sheet metal box attached to your furnace or air handler. The supply plenum carries conditioned air into the ducts, and the return plenum brings air back. Installers shape it with hand seamers so the pieces overlap, then fasten and seal every seam with mastic or foil tape so air goes where it should.

Want it done at your place? See HVAC Installation Craft at SwiftPro or call (703) 997-9757.

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SwiftPro Heating, Cooling & Plumbing
4230 Lafayette Center Dr N, Chantilly, VA 20151
44679 Endicott Dr, Suite 211, Ashburn, VA 20147
Virginia Class A contractor license #2705192276

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