Duct Sealing And Balancing

What this is

In a home with ducted warm air or ducted cooling, the ducts are as much a part of the system as the equipment. Air escaping from a joint in a loft or crawl space never reaches a room. Balancing is the separate step of adjusting dampers and register openings so the rooms furthest from the unit are not starved while the nearest ones are over-served.

Telling whether your home needs it

One room that never quite reaches temperature while another overshoots is the classic pattern. So is a duct run in an unheated space that feels warm on the outside when the system is running, or a visible layer of dust drawn to a joint. Registers that whistle usually indicate flow being forced through too small an opening somewhere.

What the job involves

Work along the accessible runs looking at every joint, seam, take-off and connection at the register boot. Sealing is done with mastic or with a foil tape rated for ductwork, applied to a clean surface. Balancing follows sealing, never the other way round, and is done with the system running: adjust one damper, wait for conditions to settle, then measure again.

Things to watch

Fabric-backed general-purpose tape is not a duct sealing material and will let go within a few seasons. Never close registers to the point where the system is fighting against a closed circuit; balancing is about proportion, not shutting rooms off. Ducts running through unheated lofts or voids should also be insulated once sealed, or they simply deliver cooled air efficiently.