Ductwork repair, replacement and sealing

ENERGY STAR puts it at about 20 percent of the air moving through a typical house's ducts, lost to leaks, holes and poorly connected sections. The loss is larger where more of the ductwork runs through an unheated attic, crawlspace or garage.

Damage, contamination, internal lining, sizing and access determine whether cleaning, repair or replacement makes sense.

Often. Airflow and capacity must be checked because the new system may require different air volume than the old furnace.

It is a calibrated fan temporarily connected to the duct system, with all registers sealed, that pressurises the ducts and measures how much air escapes. The result is expressed as leakage at a reference pressure and often as a percentage of the system's airflow, which turns a vague concern into a number you can act on and verify. It is distinct from a blower door test, which measures leakage of the whole building envelope. A thorough energy assessment on a ducted Vermont house usually involves both, because they diagnose different problems.

Symptoms first: rooms that never reach temperature, large differences between rooms, high bills relative to comparable houses, dusty rooms, and visible dirt streaking at duct joints, which marks where air has been escaping for years. In an accessible basement you can often feel it: run the system and put a hand along the joints. But the definitive answer is a duct leakage test with a calibrated fan, and it is worth asking for, because it converts a guess into a percentage and gives you a way to verify the repair.

The accessible joints, yes, and it is worthwhile work. Use mastic, the thick paint-on sealant, or foil-backed tape rated for ducts, applied to clean surfaces at every joint, seam and connection you can reach in the basement, crawlspace or attic. What you must not use is standard cloth duct tape, which despite the name dries out and fails on ducts within a few years. What a homeowner cannot do is find and seal leaks inside walls and floors, which is what aerosol sealing addresses, or measure the result.

You pay to condition air that never reaches a room. Duct leakage in unconditioned space is one of the largest single efficiency losses in a typical house, and in Vermont, supply ducts leaking into an unheated attic or a vented crawlspace are heating the outdoors directly. There is a second, less obvious cost: leaky return ducts in a crawlspace or attached garage pull in whatever air is there, dust, moisture, radon, and in the garage case, vehicle exhaust, and distribute it through the house.

Manual sealing of accessible ducts in a typical house is commonly a day. Aerosol sealing, where a sealant is atomised into the pressurised duct system and deposits itself at the leaks from the inside, is usually a half to full day and is the option for ducts that are largely inaccessible. Both should begin and end with a measurement, a duct leakage test before and after, because the whole point is a number, and a job with no before figure has no way to demonstrate it accomplished anything.

Efficiency Vermont and the electric utilities have historically supported air sealing, insulation and duct work as part of whole-home efficiency programmes, often through certified Home Performance contractors and sometimes bundled with an energy audit, not offered as a standalone rebate. Terms change, and duct sealing is more often supported as part of a package than on its own. Confirm what is currently available with Efficiency Vermont or your electric utility before scheduling, and ask whether an audit is a prerequisite.

Sealing work is typically warrantied on the labor rather than as a performance guarantee, since duct leakage can be measured before and after but is not a single point of failure the way a part is: ask for the before-and-after leakage numbers as the actual proof of the work, not just a warranty card.

Sealing accessible joints in the basement while ignoring leaks inside walls and floors that are actually driving the bigger losses. A visible improvement in the basement does not mean the system's total leakage dropped meaningfully if the larger leaks were never reached.