How do you splice AC flex ducts?

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Apply a piece of foil-backed duct tape to the seam, keeping the middle of the tape centered over the seam. Press the tape with a squeegee. Cover the tape with a piece of mesh. Coat the mesh with a 1/8-inch thick layer of duct mastic, using a paintbrush as an applicator.

Subsequently, question is, can you use flex duct return air? Flex duct effectively creates a tight radius elbow where it turns into the top of a diffuser. The high pressure loss is further increased because the flex fabric gathers at the inside of the throat and reduces the effective diameter.

Beside above, how do you seal a flex duct?

Seal the duct-collar junctions with mastic. Pull insulation wrapped in vapor barrier over the connections and seal seams with both UL-181-approved tape and mastic. Do not compress the insulation.

Is flexible ductwork good?

Cons of Flexible Ductwork Flexible ductwork can restrict airflow more than metal ducts. Greater airflow means better HVAC system efficiency, but flexible ducts are more susceptible to interference from compression, pinching, and twisting. For a more long-term solution, metal ductwork is a much better choice.