3.1601.5 Preparation and Mechanical Fastening

Duct Preparation
Desired Outcome: 
Ducts and plenums properly fastened to prevent leakage

Surrounding insulation will be cleared to expose joints being sealed; salvage for reuse if possible

Duct surface to receive sealant will be cleaned

Gain access while maintaining insulation value

Achieve proper adhesion for airtight seal when needed to ensure a tight fit to the framing structure and ensure the register can be removed and reinstalled by the dwelling occupant

Metal to metal

Ducts will be fastened with a minimum of three equally spaced screws

Ensure durable joints

Flex to metal

Joints will be fastened with tie bands using a tie band Tie band A strap, often made of nylon, that mechanically squeezes a flexible duct to a fitting. Must have a minimum performance temperature rating of 165° (per UL 181A-type test) and a minimum tensile strength rating of 50 pounds tensioning tool

For oval flexible duct to metal connections, tie bands cannot be used; appropriate mechanical fastener will be used

All connections, regardless of fastener, will be sealed

Ensure durable joints

Duct board to duct board

Joints will be fastened with outward clinching (stitch) staples and c-channels if possible

Ensure durable joints

Duct board to flexible duct

Metal take-off collar specifically designed for the thickness of the duct board will be used

All finger tabs will be bent down securely

Finger tabs will be longer than the thickness of the duct board and the shank will not extend beyond the thickness of the duct board

There will be an internal metal backer inside the duct board through which three evenly spaced screws can be secured; the metal backer will not interfere with air flow

Ensure durable joints

Prevent the collar from moving into or out of the duct board or slipping

Duct board plenum to air handler cabinet

Flange/c-channel will be fastened with screws with the duct board installed between c-channel flanges

Duct board plenum will be connected to air handler plenum with flexible duct in upflow units

Ensure durable joints

Boot to wood

Predrill for screws or use ring shanked nails to fasten boot to wood

Ensure durable joints

Boot to gypsum

If accessible, boot hanger will be fastened to adjacent framing with screws or nails

Boot will be connected to boot hanger with screws

If inaccessible, boot will be fastened to gypsum with a durable, adhesive sealant

Ensure durable joints

Duct board to flex

Metal take-off collar with a hip and an internal metal backer will be used

Take-offs will be in accordance code requirements

Ensure durable joints