duct handler, boots and elbows & air Sealing

Air handlers – the large metal boxes containing the blower and several heating and cooling elements – are connected to ductwork, and should be carefully sealed in their holes, cracks and other openings.

Air handlers have more air leakage potential than any other component of your cooling and heating system.

For general guidelines on duct sealing, see: Duct sealing

Sealing air handlers

Duct Air Handler Sealing Images credit: DOE

To seal an air handler and their access panels use mastic or approved tape - or proper caulks.

Seal all seams in the air handler cabinet and in plenums; seal the openings for wiring, plumbing and line penetrations, and tape around access panels.

Connections between the air handler box and the supply and return plenums and ducts should be sealed with mastic. You may seal these areas from the inside (after having removed service panels).

Plenums

Plenums - typically made from fiberglass duct board… - should be carefully sealed in their joints using mastics (or approved tapes).

Close cavities used as plenums

Some closets (and closed areas) are used as return plenums, in many homes. If this is your case, you may try to minimize the inefficiency of this non-recommended solution by sealing carefully these plenums. This is important to prevent unconditioned air to be driven into the distribution system.

Just caulk or foam all the penetrations and gaps in the ceiling, floor and walls associated with these rather improvised plenums.

Duct boots and elbows

The problem with duct boots and elbows is basically in their joints, and the joints between them and the ducts, which should be properly sealed. Use a good mastic.

The connection between the duct and the boot – when too wide – can require mesh.

The duct boot connections with the walls, floors and ceiling should also be well sealed with proper caulks. In some cases, boots are more easily sealed from the inside, after installation.