What is source removal in 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 while every run is mechanically agitated, so debris is carried out of the building rather than redistributed within it. It is the method the NADCA ACR Standard describes, and it is the reason collection airflow matters: agitating a duct without enough airflow to carry material away moves the debris somewhere else in the system instead of removing it.
How to use this
These are the words that turn up on quotes, inspection reports and in conversation with technicians. They are grouped by subject rather than listed alphabetically end to end, because most people arrive looking for a particular corner of the vocabulary rather than a specific word.
If a term you were given is not here, ask us. We would rather define it than talk around it.
Method and standards
- ASCS
- Air Systems Cleaning Specialist. A NADCA certification earned by examination on the ACR Standard. Refresh Duct Cleaning has an ASCS on staff.
- CVI
- Certified Ventilation Inspector. A NADCA credential earned by individual examination, covering inspection and assessment of HVAC systems rather than the cleaning itself.
- NADCA
- The National Air Duct Cleaners Association, the trade body that publishes the ACR Standard and certifies individuals. NADCA certifies people, not companies — a company holds membership, an individual earns the ASCS or CVI credential. Any company advertising itself as "NADCA-certified" is describing something that does not exist.
- 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.
- Remediation
- The removal or treatment of contamination in building materials, as distinct from cleaning an HVAC system. Mould remediation is a separately licensed activity in Florida. We clean and restore HVAC systems; we are not a licensed mould remediator.
- Restoration
- Returning a duct system to serviceable condition where cleaning alone is not enough — sealing, encapsulating, repairing or replacing components. Distinct from remediation, which deals with the building rather than the system.
- 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.
- Verification of cleaning
- Under the ACR Standard, cleaning is verified by inspection of the system after work rather than by assertion. In practice that means photographs of the same locations before and after, which is why we document rather than describe.
Equipment and tooling
- Access port
- An opening cut into the ductwork or air handler to admit tools and the collection hose, then sealed and labelled afterwards. Cleaning a system properly requires access; how those openings are closed afterwards is a fair thing to ask about.
- Agitation
- Mechanically dislodging debris from the interior duct surface so the airstream can carry it away. Compressed-air whips, skipper balls and rotary brushes are all agitation tools. Agitation without adequate collection airflow redistributes debris rather than removing it.
- Air whip
- A compressed-air tool with flexible tails that flail against the duct interior as air passes through them. The standard agitation tool for flex duct, because unlike a rotating brush it does not abrade the inner liner.
- HEPA
- High-Efficiency Particulate Air. A filter grade defined by its capture efficiency at the most penetrating particle size. On a collection unit it matters because it determines what the machine exhausts rather than what it captures.
- Portable unit
- A wheeled vacuum carried into the house, typically drawing a fraction of the airflow of a truck-mounted system. Adequate for small or isolated sections; not for whole-system source removal.
- Skipper ball
- A compressed-air nozzle that propels itself along a duct run, directing jets backwards toward the collection unit. Used to reach lengths of rigid duct that a whip cannot.
- Truck-mounted vacuum
- A large collection unit built into a truck or trailer, exhausting outside the building, used to place the duct system under continuous negative pressure. The distinction that matters is collection airflow: whole-system negative pressure needs air volume that a portable unit cannot generate.
Parts of an HVAC system
- Air handler
- The cabinet containing the blower, evaporator coil and filter rack. In most Florida homes it sits in a garage, closet or attic. Everything the system distributes passes through it, which is why cleaning ductwork and skipping the air handler misses the point.
- 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.
- Cabinet interior
- The inside surfaces of the air handler itself — blower housing, coil face, drain pan area and internal liner. Frequently the dirtiest part of a system and frequently excluded from a cheap duct cleaning quote.
- Condensate drain
- The line carrying water away from the drain pan beneath the evaporator coil. A Florida air conditioner removes a substantial volume of water on a humid day, and a blocked condensate line is one of the more common causes of water damage from an attic air handler.
- Condenser coil
- The outdoor coil that rejects heat to the air. Distinct from the evaporator coil indoors. A dirty condenser raises head pressure and energy use without producing any of the symptoms people associate with dirty ducts.
- 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.
- 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.
- 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.
Ductwork and materials
- 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.
- Duct board
- Rigid fibreglass board used to fabricate ductwork and plenums, with the fibrous surface facing the airstream. Common in Florida construction of a certain era. Cleanable while sound, replaceable once the surface has eroded or been wet.
- 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.
- Duct liner
- Fibrous insulation applied to the inside surface of a duct, so the airstream contacts the insulation directly. Cleanable with care while intact; once it has been wet or contaminated, EPA, NADCA and NAIMA all recommend replacement rather than cleaning.
- 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.
- 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.
- 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.
- R-value
- A measure of thermal resistance. Florida requires supply ducts of 3 inches or more in unconditioned attics to be insulated to R-8 under the prescriptive path of the energy code. R-value is only delivered at the rated thickness, so insulation crushed over a truss is not performing at its label.
- Register and grille
- A register is the terminal with adjustable louvres where supply air enters the room. A grille is fixed, and usually covers a return. Both are the visible end of a system whose condition they tell you almost nothing about.
- Rigid duct
- Sheet metal ductwork. Durable, cleanable with a wider range of tools than flex, and found mostly in trunk lines and older systems.
- Takeoff
- The fitting where an individual branch run leaves the trunk or plenum. A common leakage point, and a common place to find debris because of the change in air direction.
- Vapour barrier
- The outer jacket on insulated flex duct. It keeps humid air away from the cold inner surface. Once it is split, poorly taped or UV-degraded, the insulation absorbs moisture and stops performing — a common cause of sweating attic ducts.
Airflow and pressure
- 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.
- Balancing
- Adjusting dampers and register settings so each room receives its intended share of airflow. A balancing problem and a duct cleanliness problem present very similarly from inside the room.
- CFM
- Cubic feet per minute, the unit of air volume flow. Used both for what a system delivers and for what a collection unit draws.
- Negative air
- Holding a space or a duct system at lower pressure than its surroundings so that air — and anything airborne in it — moves inward rather than outward. The operating principle of source removal.
- 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.
- Pressure drop
- The loss of static pressure as air passes through a component. A loaded filter or a matted coil face raises pressure drop, which reduces airflow through the whole system.
- Short cycling
- An air conditioner switching on and off in brief bursts rather than running in sustained cycles. It reduces moisture removal, because dehumidification depends on sustained run time across a cold coil.
- 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.
Moisture, humidity and climate
- Condensation
- Water forming on a surface colder than the dew point of the air touching it. On ductwork it indicates an insulation, vapour barrier or leakage problem rather than a plumbing one.
- Dew point
- The temperature at which air becomes saturated and water condenses out of it. When the outer surface of an attic duct falls below the attic air dew point, the duct sweats. This is the mechanism behind most wet ductwork in Florida.
- Hygroscopic
- Readily absorbing moisture from the air. Fine construction dust, particularly gypsum, is hygroscopic, which is why it cakes on a damp evaporator coil rather than staying loose.
- 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.
- Microbial growth
- Biological growth on a surface, which requires moisture to establish. The accepted critical threshold is sustained surface relative humidity around 70 per cent. Controlling moisture, not cleaning frequency, is what prevents it.
- 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.
- Sensible and latent heat
- Sensible heat changes temperature; latent heat changes moisture content. Florida cooling is heavily latent, which is why a house can hit its thermostat setpoint and still feel wet.
Air quality and filtration
- Antimicrobial fogging
- Dispersing a treatment through the duct system as a fine aerosol. It is a treatment applied after cleaning, never a substitute for it, and only EPA-registered products labelled for HVAC use belong in a duct system.
- 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.
- Filter rack
- The housing holding the filter. A rack that does not seal around the filter lets air bypass it, which puts unfiltered air straight onto the coil regardless of the filter grade.
- 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.
- Particulate
- Solid or liquid matter suspended in air, described by size. Smaller particles stay airborne longer and pass through filtration more readily, which is why fine soot deposits on ceilings while visible dust settles on furniture.
- PM2.5
- Particulate matter 2.5 micrometres and smaller. Fine enough to remain airborne for extended periods and to pass through lower-grade filter media.
- 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.
- VOC
- Volatile organic compound. Gases emitted from paints, adhesives, finishes and furnishings. Particulate filtration does not remove gases, which is why new-build odour complaints are not a duct cleaning problem.
Dryer exhaust
- Backdraft damper
- A flap at the exhaust terminal that opens under dryer airflow and closes when the dryer stops, keeping outside air, pests and conditioned air from moving the wrong way.
- Dryer booster fan
- A fan installed in a dryer exhaust run that exceeds the length the code allows unassisted. An engineered solution for a run that cannot be shortened, not a substitute for cleaning it.
- Equivalent length
- The effective length of a duct run once fittings are accounted for. Each elbow adds resistance equal to some length of straight duct, and the deduction depends on the elbow radius and type rather than being a flat figure.
- Lint trap housing
- The cavity the removable lint screen sits in. Lint passes the screen and accumulates in the housing, which is a common ignition location and is not reached by cleaning the screen.
- Transition duct
- The short flexible connector between the dryer and the wall duct. Code permits a single listed length no longer than 8 feet, never concealed inside construction. It is the only flexible section allowed in a dryer exhaust.
Commercial and documentation
- Pre and post documentation
- Photographs of the same identified locations before and after the work, dated and labelled. The deliverable a facility manager needs in order to justify the expenditure and demonstrate it was performed.
- Rooftop unit (RTU)
- A packaged air handling unit mounted on a commercial roof. Access, scheduling and documentation requirements differ substantially from residential work.
- Scope of work
- A written description of exactly what will be cleaned, by what method, and how it will be verified. A defined scope is what makes commercial bids comparable to each other.
- VAV box
- Variable air volume terminal unit, regulating airflow to a zone in a commercial system. A cleaning scope that ignores terminal units has not addressed the whole system.
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 certifies people, not companies. The company joins NADCA as a member; an individual sits an examination on NADCA's ACR Standard and earns the Air Systems Cleaning Specialist (ASCS) credential. So “NADCA-certified company” is not a real thing, and a company advertising it is telling you something about how carefully it reads. Refresh is a NADCA member company with an ASCS on staff, which is the accurate way to say it. What it buys you is a documented method behind the work rather than improvisation.
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.
