What is source removal in air duct cleaning?
Source removal is the method that defines professional air duct cleaning. The duct system is placed under continuous negative pressure using a HEPA-filtered collection unit, and each supply and return run is mechanically agitated with brushes or compressed-air tools so debris is drawn out of the system and out of the building. Cleaning that only vacuums a short distance behind each register, or that blows air through the system without capturing what it dislodges, is not source removal.
Definitions
If a technician used a word you did not recognise, it is probably here. If it is not, ask us and we will explain it plainly rather than talk around it.
- Source removal
- The method that defines professional air duct cleaning. The duct system is placed under continuous negative pressure with a HEPA-filtered collection unit while each run is mechanically agitated, so debris leaves the building rather than relocating inside it. Cleaning that does not capture and remove material is not source removal.
- NADCA ACR Standard
- The published standard from the National Air Duct Cleaners Association that defines how HVAC systems should be assessed, cleaned and restored. It is the document that separates a defined method from improvisation.
- ASCS
- Air Systems Cleaning Specialist. A NADCA certification earned by examination on the ACR Standard. Refresh Duct Cleaning has an ASCS on staff.
- Negative pressure
- Lowering the air pressure inside the duct system relative to the building, so air flows into the ductwork and out through the collection unit. It is what stops dislodged debris entering the living space during cleaning.
- Plenum
- The large box immediately at the air handler where ductwork connects, on both the supply and return sides. Plenums hold more accumulated material than the branch runs and are the most commonly skipped part of a cheap cleaning.
- Supply and return
- Supply ducts carry conditioned air from the air handler to the rooms. Return ducts carry air back. The return side pulls continuously and typically accumulates more dust and hair than the supply side.
- Evaporator coil
- The indoor coil that removes heat and moisture from the air. In Florida it is wet for most of the year, which is why it collects material and why a fouled coil restricts airflow and loses heat transfer.
- Blower wheel
- The squirrel-cage fan that moves air through the system. It accumulates a dense film on every blade, evenly and gradually, so the airflow loss is rarely noticed until it is substantial.
- Drain pan and condensate line
- The pan beneath the evaporator coil and the line that drains it. Standing water here is a common source of the smell people describe as musty when the air conditioning starts.
- Fiberglass duct board
- Rigid ductwork made from fiberglass, widely used in Florida construction. Its interior surface degrades over time in humidity, at which point the duct itself becomes a source and cleaning alone gives a short-lived result.
- Encapsulation
- Applying an HVAC-rated coating to the interior of cleaned fiberglass duct board or lined ductwork, binding the deteriorating surface so it stops shedding into the airstream. Often a practical alternative to replacing a whole duct system.
- Flex duct
- Flexible insulated ductwork with an inner liner. Common in Florida. Crushed, torn or disconnected flex cannot be restored by cleaning or coating and is replaced.
- Duct leakage
- Conditioned air escaping the duct system, and unconditioned air entering it. In most Florida homes with attic ductwork, leakage costs more than anything happening inside the ducts.
- Aeroseal
- An aerosolized sealant introduced into a pressurized duct system. Escaping air carries sealant particles to the edges of leaks, where they accumulate and bridge the gap, reaching leaks in attic, wall and slab runs that cannot be accessed by hand. Leakage is measured before and after.
- Boot
- The connection between a duct run and the ceiling or wall register. Boots are where air leakage and condensation most often occur together, and are a frequent cause of ceiling stains around vents.
- MERV
- Minimum Efficiency Reporting Value, the rating scale for air filters. Higher is not automatically better: a filter too restrictive for the blower reduces airflow and costs capacity. The right rating is the highest the equipment tolerates.
- Filter bypass
- Air travelling around a filter rather than through it, usually through gaps at a poorly sealed filter rack. Bypass makes the filter's MERV rating largely irrelevant and is extremely common.
- Latent load
- The portion of an air conditioner's work that removes moisture rather than heat. An oversized system satisfies the thermostat quickly and shuts off before removing much moisture, leaving a house cold and damp.
- Relative humidity
- The moisture content of air relative to what it can hold at that temperature. Indoor relative humidity persistently above 60 percent supports biological growth on surfaces throughout a building.
- UV-C
- Ultraviolet light in the germicidal range, installed inside air handlers to limit growth on the surfaces it illuminates, typically the coil face. It treats illuminated surfaces, not ductwork out of its line of sight.
- Static pressure
- Resistance to airflow within a duct system. High static pressure indicates restriction, whether from a fouled coil, an over-restrictive filter, crushed flex or undersized ductwork.
- Air changes per hour
- How many times the full volume of air in a space is replaced in an hour. Used to size ventilation and to describe how quickly contaminants are diluted.
Common questions
What is the difference between duct cleaning and duct sealing?
Cleaning removes debris from inside the ductwork. Sealing stops conditioned air escaping the ductwork and unconditioned air entering it. They solve different problems and the symptoms overlap, which is why an inspection comes first. In many Northeast Florida homes with attic ductwork, sealing returns more than cleaning.
What is the difference between cleaning and encapsulation?
Cleaning removes what has accumulated on a duct surface. Encapsulation coats a duct surface that has itself degraded, so it stops shedding. If fiberglass duct board has broken down, cleaning treats the symptom and encapsulation treats the cause.
What does NADCA certified actually mean?
NADCA publishes the ACR Standard defining how HVAC systems should be assessed and cleaned. An Air Systems Cleaning Specialist has passed an examination on that standard. It means there is a documented method behind the work.
Sources and standards
Where this page relies on published guidance, here is what it relies on.
- NADCA ACR Standard — The industry standard defining HVAC system cleaning methodology.
- US EPA — Should You Have the Air Ducts in Your Home Cleaned? — Federal guidance on when duct cleaning is and is not warranted.
- US DOE — Minimizing Energy Losses in Ducts — Department of Energy guidance on duct sealing and insulation.
- US CPSC — Dryer Fire Safety — Consumer Product Safety Commission on dryer exhaust fire risk.
