Independent guide · we don’t clean ducts

Duct Sealing vs Duct Cleaning

Direct answer

Duct sealing closes the leaks in your duct system. Duct cleaning removes deposits from inside it. They are performed on the same ductwork, often by the same trades, and the evidence behind them is not comparable. ENERGY STAR estimates that in a typical house about 20 to 30 percent of the air moving through the duct system is lost to leaks and holes. Nothing equivalent exists for cleaning. If your complaint is comfort, airflow or energy bills, sealing is the purchase with a federal figure attached to it.

The comparison, side by side

Duct sealing and duct cleaning compared on purpose, evidence, materials and what each one leaves behind
  Duct sealing Duct cleaning
What it does Closes gaps at joints, seams, collars, boots and register connections so conditioned air reaches rooms. Removes dust, debris and contamination from the interior surfaces of the system.
What problem it fixes Air leaving the system before it gets to you. Rooms that will not heat or cool, high bills, stuffy rooms. A specific identified condition inside the ducts: mold on hard surfaces, vermin, or debris being released into rooms.
Published quantification About 20 to 30 percent of moving air lost in a typical house; efficiency reduced by as much as 20 percent (ENERGY STAR) Typical range None. EPA recommends cleaning as needed rather than routinely, and no benefit figure exists.
Indoor air quality claim ENERGY STAR states sealing can help improve indoor air quality by reducing the risk of pollutants entering ducts. EPA states duct cleaning has never been shown to prevent health problems.
Is it included in the other? No. ACR, the NADCA standard, states restoration does not include sealing air leaks. No. Sealing contractors wipe or vacuum surfaces as preparation, which is not a cleaning service.

The number, and exactly what kind of number it is

ENERGY STAR — a joint program of EPA and the U.S. Department of Energy (DOE) — publishes the sentence this comparison turns on: In a typical house, however, about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.

Alongside it, ENERGY STAR’s duct sealing flyer states that leaky ducts can reduce heating and cooling system efficiency by as much as 20 percent, and that sealing and insulating increases efficiency, lowers bills, and can often pay for itself. It also notes that sealing can help improve indoor air quality by reducing the risk of pollutants entering ducts.

Read that last point next to EPA’s position on cleaning. ENERGY STAR attributes an indoor-air-quality benefit to sealing the ducts — the benefit EPA declines to attribute to cleaning them. Same ductwork, same house, opposite evidentiary status.

Now the honesty part, because this site does not quote a favorable number without inspecting it.

Two integrity points about the 20 to 30 percent figure

It has drifted. The same program published a different version of the same sentence in 2009: in typical houses, about 20 percent of the air that moves through the duct system is lost due to leaks, holes and poorly connected ducts. That is EPA document 430-K-09-004, August 2009. The current live page says 20 to 30 percent. Same program, same sentence structure, a wider number.

No page shows its work. No ENERGY STAR page we fetched gives a source, a sample or a method for either figure. It is a published federal estimate, and we cite it as one — not as a measured national statistic. That distinction is exactly the one we apply to EPA’s un-updated duct cleaning price range, and it would be dishonest to apply it only when the number is inconvenient.

A third figure brackets the others. DOE’s Building America program, in a December 2011 measure guideline, states that the typical home has 20 percent duct leakage and that in older homes it is not uncommon for leakage to reach 30 to 50 percent of total system airflow Typical range A fourth, older DOE publication from November 1999 put typical duct system losses at 25 to 40 percent of the heating or cooling energy the equipment produces. We report all of them, dated, rather than picking one or averaging them — different documents from different decades, measuring related but not identical quantities. Incidentally, ENERGY STAR’s own savings model assumes a house with 23 percent total system duct leakage, which sits inside the range.

The 15 percent figure everyone gets wrong

If you have read much about duct sealing you have met a claim along the lines of “homeowners can save an average of 15 percent on heating and cooling costs by sealing and insulating.” It is a real ENERGY STAR figure. It is not a duct sealing figure.

ENERGY STAR’s published methodology for estimated energy savings models a specific package: air sealing the house envelope — leaks to the attic, through the foundation, and around windows and doors — plus attic, basement floor and basement wall insulation. For that package it models an average saving of 15 percent on heating and cooling costs, or about 11 percent on total energy costs.

Duct sealing is not one of the modeled measures. Duct leakage appears only as a fixed baseline assumption of the reference house — 23 percent total system leakage in a 1,700 square foot home built between 1970 and 1989 — held constant rather than improved. ENERGY STAR also caveats that savings are an average and are higher in the North than the South.

So 15 percent and 11 percent belong to the building envelope. Anyone citing them for duct sealing has attached the right number to the wrong job. We flag it rather than repeat it, because a page that corrects a favorable-sounding error is worth more than one that launders it.

This is the distinction that gets collapsed most often, and EPA draws it for us in a single sentence on the duct cleaning page itself. Using sealants to encapsulate the inside surfaces of ducts, EPA notes, is a different practice from sealing duct air leaks — and it is sealing duct air leaks that can help save energy on heating and cooling bills.

Two practices that share a word and share nothing else
  Sealing duct air leaks Sealants to encapsulate contaminants
Where it is applied The outside of joints, seams, collars and boots — or injected as an aerosol that migrates to the leaks from within. Coating the interior surface of the ductwork to lock down dirt or growth.
Purpose Stop conditioned air escaping the system. Encapsulate what is already inside the duct rather than removing it.
Official position Recommended by ENERGY STAR and DOE; EPA notes it can save energy. EPA, NADCA, NAIMA and SMACNA do not currently recommend the routine use of sealants to encapsulate contaminants in any type of duct.
Known unknowns No federal cost figure; no national dollar savings figure. EPA notes little is known about the potential toxicity of these products under typical use conditions or if they catch fire.

The practical consequence: if a contractor offers to “seal your ducts” at the end of a cleaning visit, find out which one is meant. Mastic and listed tape at leaking joints is the recommended work. A sprayed interior coating over accumulated contamination is the practice four bodies decline to recommend routinely.

What sealing actually involves

Enough of the process is published federally that you can evaluate a quote against it.

  • Find the leaks. DOE’s Building America guideline reports the most common leakage locations are collars, transitions, and connections to other materials. ENERGY STAR’s signs of a duct problem: high utility bills, rooms difficult to heat or cool, stuffy rooms, ducts running through an attic, crawlspace or garage, and tangled or kinked flexible ducts.
  • Use the right material. DOE calls duct mastic the preferred material for seams and joints, more durable than any available tape. ENERGY STAR permits mastic, metal tape or an aerosol-based sealant. Both are emphatic about what not to use: never gray duct tape, and avoid cloth-backed rubber adhesive duct tape, which tends to fail quickly.
  • Seal first, insulate second. DOE’s guideline is explicit that ducts should be thoroughly sealed before insulating, and that reducing leakage often has much larger comfort and energy impacts than insulating.
  • Insulate what runs through unconditioned space. ENERGY STAR’s target is R-6 or higher for ducts in attics, crawlspaces and garages Verified fact The 2011 DOE guideline describes a stricter requirement of its era, R-8 in attics and R-6 elsewhere, but energy codes are adopted state by state and we verified no state’s current adoption — treat it as a dated guideline figure, not the rule where you live.
  • Test combustion safety afterward. ENERGY STAR calls for confirming there is no backdrafting of gas or oil-burning appliances and conducting a combustion safety test after sealing. Tightening the distribution system changes house pressures.
  • Hire out the hard parts. DOE says minor duct repairs are easy to make but that qualified professionals should seal and insulate ducts in unconditioned spaces. ENERGY STAR suggests NATE or BPI certified contractors.

Aerosol sealing, described and not oversold

Aerosol-based duct sealing works by pressurizing the duct system and injecting a spray sealant that migrates to the leaks and closes them from inside. A DOE and National Renewable Energy Laboratory record describes it as able to seal leaks up to half an inch in diameter in hard-to-reach locations using a nontoxic vinyl polymer, and credits Lawrence Berkeley National Laboratory with developing the core technology under DOE funding.

What we will not tell you is whether it beats manual mastic sealing. We found no independent measurement comparing the two, and no cost figure from any federal source for either. A leakage-reduction percentage for aerosol sealing is something we could not verify anywhere.

Sequence: does cleaning come before sealing?

DOE’s Building America guideline instructs that before applying mastic, duct surfaces should be relatively clean, and that some duct systems can be tremendously dusty and dirty — in which case it is important to remove much of that grime by wiping or vacuuming. The requirement is stricter for tape: surfaces should be clean and dry before applying it. The same guideline notes, in fairness, that some contractors report cleaning is less critical for mastics. It does not address surface preparation for aerosol sealants at all.

NADCA’s own guidance agrees on the mechanics: the surface must be clean and dry for proper adhesion, and dust should be wiped from the seams before the sealant goes on.

Here is the twist. What that makes cleaning is a surface preparation step for a repair — wiping and vacuuming where the sealant will go — not a professional cleaning of the whole system. It would be easy for us to reach for this as a sales argument for our own subject, and it does not support one. Nobody in these documents says ducts must be professionally cleaned before they can be sealed.

The sentence that settles who does what

ACR, the NADCA standard, states in section 4.24.1 that restoration does not include the sealing of air leaks within duct systems or HVAC systems. We read that clause in the 2021 edition, published on NADCA’s own site; the 2025 edition is the current one.

In plain terms: the industry’s own standard defines duct cleaning as excluding duct sealing. If you paid for a cleaning, you did not buy sealing, and no part of the standard the contractor works to obliges them to close a single leak. The reverse holds as well — a sealing contractor wiping a seam has not cleaned your system.

The practical ordering, then: if the system is genuinely dirty and you have decided it warrants cleaning on its own merits, clean first, then seal, then insulate. If it is not, seal and insulate anyway, with whatever local wiping the sealing contractor needs to make the material stick.

What we will not publish about savings

There is no national dollar figure for what duct sealing saves, and we are not going to manufacture one.

What exists is fragmentary. ENERGY STAR’s flyer says sealing and insulating can often pay for itself — qualitative. DOE’s Energy Saver page says ducts leaking heated air into unheated spaces can add hundreds of dollars a year to bills, and that insulating ducts in unconditioned spaces is usually very cost-effective — a direction, not a figure for your house. The one dollar figure we verified is scoped to a single city: in the 2011 DOE Building America guideline, duct sealing in Houston can save $200 to $400 per year in HVAC costs in a modeled scenario reducing leakage from 30 percent to 6 percent Single source One climate, one model, 2011. It cannot be generalized, and we do not.

The 1999 DOE publication offered a national estimate — roughly $160 off a typical home’s heating and cooling bill from halving the typical loss, with about a three-year payback. Inflation alone makes that dollar amount meaningless today, and we record it as history rather than guidance.

How the two services compare on evidence

What the published record supports for each intervention on the same ductwork
Claim Duct sealing Duct cleaning
Saves energy ENERGY STAR and DOE both say so, with a quantified loss figure behind it. A 2010 peer-reviewed review found inadequate evidence that it improves airflow or reduces energy consumption.
Affects indoor air quality ENERGY STAR states sealing can help by reducing the risk of pollutants entering ducts. EPA states cleaning has never been shown to prevent health problems, and that studies do not conclusively show particle levels falling after cleaning.
Risk of making things worse Requires a combustion safety test afterward, which ENERGY STAR specifies. EPA warns a careless provider can damage the system and possibly increase heating and cooling costs, and that an inadequate vacuum can release more dust than leaving ducts alone.

None of which means nobody should ever clean a duct. EPA names three conditions where cleaning should be considered — substantial visible mold in hard-surface ducts or on components, vermin infestation, and excessive debris with particles being released into the home. When one is present, cleaning is the remedy and sealing is not. Whether your situation is one of those is the question to settle first.

Common misconceptions

“My duct cleaner sealed the ducts too”

Almost certainly not in the sense that saves energy. The industry standard excludes air-leak sealing from the scope of cleaning and restoration. What a cleaner does seal is the service openings cut to get tools inside, which must be closed with gaskets, duct sealants, mastic or tape meeting UL 181A or 181B — a workmanship requirement, not an energy measure.

“Sealing saves 15 percent on my energy bills”

That figure belongs to envelope air sealing and insulation, not duct sealing. In ENERGY STAR’s model, duct leakage is a fixed baseline assumption and is never improved.

“Ducts have to be professionally cleaned before they can be sealed”

Overstated. DOE’s guideline asks for surfaces that are relatively clean, and says grime should be removed by wiping or vacuuming. It notes some contractors find cleaning less critical for mastics. That is surface preparation, not a required service.

“If the ducts leak, they need replacing”

Not usually. Sealing is the cheaper, better-evidenced intervention, and the published triggers for replacement are about the material’s condition — wet, moldy, delaminating, torn, disconnected. The condition-based test for replacement is a separate question from leakage.

Which should I do first if I can only do one?

Seal, unless you have one of EPA’s three cleaning conditions. Sealing has a quantified federal loss figure behind it, an indoor air quality rationale from ENERGY STAR, and a place on the National Institute of Standards and Technology’s list of faults that degrade system performance. Cleaning has none of those.

Can I seal ducts myself?

Partly. DOE says minor duct repairs are easy to make, but also that qualified professionals should seal and insulate ducts in unconditioned spaces and should always perform changes and repairs to a duct system. The combustion safety test afterward is not a homeowner task. See where the DIY boundary sits on the cleaning side.

How much does duct sealing cost?

No federal source publishes a price, for either manual or aerosol sealing. What is published is directional: DOE says insulating ducts in unconditioned spaces is usually very cost-effective, and ENERGY STAR says sealing and insulating can often pay for itself in energy savings.

Does sealing help with dust in the house?

ENERGY STAR’s claim is about pollutants entering the ducts, a plausible mechanism but not a measured household dust reduction, and we do not convert it into one. What actually moves household dust levels takes that question on directly.

Will sealing fix a room that never gets warm?

It might, and ENERGY STAR names rooms that are difficult to heat or cool among the signs of a duct problem. But airflow problems also come from design and equipment — the National Institute of Standards and Technology lists low indoor airflow from undersized ductwork as a separate fault. A contractor who measures rather than guesses is worth the difference.

What to do next

Sources & references

  • ENERGY STAR (U.S. EPA and U.S. Department of Energy)Duct SealingNo publication or last-updated date shown on the page, accessed August 2026Source for the exact wording of the 20 to 30 percent air loss estimate, the signs of a duct problem, sealing with mastic or metal tape, insulating accessible ducts, and the instruction never to use duct tape. The page gives no source, sample or method for the figure.
  • ENERGY STAR (U.S. EPA and U.S. Department of Energy)Duct Sealing with ENERGY STAR (flyer)No publication number or date printed on the documentSource for leaky ducts reducing efficiency by as much as 20 percent, the indoor air quality statement about reducing the risk of pollutants entering ducts, insulating unconditioned-space ducts to R-6 or higher, aerosol-based sealant as an accepted material, and the post-sealing combustion safety test.
  • U.S. EPA / ENERGY STARA Guide to Energy-Efficient Heating and Cooling (EPA 430-K-09-004)August 2009The same program's earlier version of the same sentence, giving about 20 percent rather than 20 to 30 percent. Cited to disclose that the published figure has drifted upward.
  • ENERGY STAR (U.S. EPA and U.S. Department of Energy)Methodology for Estimated Energy SavingsNo date shown on page, accessed August 2026Establishes that the widely quoted 15 percent heating and cooling savings, or 11 percent of total energy costs, is modeled for envelope air sealing and added insulation. Duct sealing is not one of the modeled measures; duct leakage is a fixed baseline assumption of 23 percent in the model home.
  • U.S. Environmental Protection AgencyShould You Have the Air Ducts in Your Home Cleaned?Page last updated February 19, 2026Source for EPA's distinction between sealing duct air leaks, which can save energy, and using sealants to encapsulate the inside surfaces of ducts; for the position that EPA, NADCA, NAIMA and SMACNA do not currently recommend routine use of encapsulating sealants; for the toxicity caveat; for the as-needed cleaning position and the three conditions; and for the damage and inadequate-vacuum warnings.
  • U.S. Department of Energy, Energy SaverMinimizing Energy Losses in DuctsNo date shown on page, accessed August 2026Source for mastic being the preferred sealing material, the warning against cloth-backed rubber adhesive duct tape, the statement that ducts leaking into unheated spaces can add hundreds of dollars a year to bills, and the advice that qualified professionals should seal and insulate ducts in unconditioned spaces.
  • U.S. Department of Energy Building America Program / Consortium for Advanced Residential BuildingsMeasure Guideline: Sealing and Insulating Ducts in Existing HomesDecember 2011Aldrich and Puttagunta. Source for typical 20 percent duct leakage and 30 to 50 percent in older homes, for the most common leakage locations, for surfaces being relatively clean before mastic and clean and dry before tape, for sealing before insulating, for the R-8 attic and R-6 elsewhere guideline of its era, and for the Houston-specific modeled saving of $200 to $400 a year, which is one climate and one scenario and cannot be generalized.
  • U.S. Department of Energy, Office of Building Technology, State and Community ProgramsImproving the Efficiency of Your Duct System (DOE/EE0109)Revised November 1999Source for the older estimate that typical duct systems lose 25 to 40 percent of the heating or cooling energy the equipment produces, and for the roughly $160 saving and three-year payback estimate. A 1999 document; its dollar figure is recorded as history, not guidance.
  • National Air Duct Cleaners AssociationACR, The NADCA Standard for Assessment, Cleaning, and Restoration of HVAC Systems, 2021 Edition2021 EditionFreely published on nadca.com. Section 4.24.1 states that restoration does not include the sealing of air leaks within duct systems or HVAC systems. Sections 4.2.5.3 and 4.2.5.4 cover sealants only for closing service openings, with tapes and mastics required to meet UL 181A or 181B. The 2025 edition is current; we verified this clause in the 2021 edition.
  • National Air Duct Cleaners AssociationA Beginner's Guide to Duct SealingPosted October 30, 2024Trade association blog, used as industry corroboration only. States the ductwork surface must be clean and dry for proper adhesion, and describes aerosol sealant particles seeking out and filling leaks from within.
  • U.S. Department of Energy / NREL (via OSTI)Aerosol-Based Sealant for Air Ducts Technology, NREL/TP-7A40-82616Publication date not shown on the record we readDescribes pressurizing ducts and injecting spray sealant, sealing leaks up to half an inch in diameter using a nontoxic vinyl polymer, and credits Lawrence Berkeley National Laboratory with developing the core technology under DOE funding. No performance comparison against manual mastic sealing exists in any source we found.
  • National Institute of Standards and TechnologySensitivity Analysis of Installation Faults on Heat Pump Performance (NIST Technical Note 1848)September 2014Lists duct leakage and low indoor airflow due to undersized ductwork among the faults with the greatest potential for significant performance degradation.
  • U.S. Environmental Protection Agency (HERO bibliographic database)Zuraimi, MS. Is ventilation duct cleaning useful? A review of the scientific evidence. Indoor Air 20(6):445-4572010A narrative review; abstract read only, full text not open access. Source for the finding of inadequate evidence that duct cleaning improves airflow in ducts or reduces energy consumption.
  • ENERGY STAR (U.S. EPA and U.S. Department of Energy)How to Keep Your HVAC System Working EfficientlyNo date shown on page, accessed August 2026Source for sealing air leaks with mastic sealant or metal tape and insulating all accessible ducts, and for the instruction never to use duct tape. Contains no mention of duct cleaning.