This article provides general educational information about duct leakage, North Carolina’s energy code, and utility costs for Raleigh-area homeowners. It is not a code interpretation, an energy audit, or financial advice. Code requirements depend on when and under which edition a home or system was permitted, and local inspection departments have the final word. Utility rate figures below come from a proposed settlement and may differ from the final order. Confirm specifics with your local building department, your utility, and a qualified professional.
If the house was built before 2012, almost certainly not. North Carolina’s 2012 update to its energy conservation code was the first to make duct leakage testing mandatory for new duct systems outside a home’s conditioned space. Homes built under earlier codes never had to pass that test, and existing homes are not required to be retested. A full replacement of the ductwork outside the thermal envelope does require one, according to a 2013 interpretation from the state. ENERGY STAR estimates that a typical house loses about 20% to 30% of the air moving through its ducts to leaks, holes, and poor connections. A duct leakage test measures that loss in a number, called CFM25, that can be compared with today’s limit for new homes. The fix for leaks is sealing and insulation. EPA says little evidence exists that cleaning only the ducts improves a system’s efficiency. With Duke Energy Progress rates proposed to rise starting in January 2027, Air Flow Solutions USA, a family-owned, fully insured company serving the Carolinas, can inspect the ducts in your attic and crawl space and give a written estimate before any work begins.
Before 2012, North Carolina’s residential energy code dealt with ductwork mostly through installation rules: materials, insulation, and how joints were to be made. Whether the finished system actually held air was not measured.
The 2012 North Carolina Energy Conservation Code changed that. As Carolina Country, the magazine of the state’s electric cooperatives, summarized it, “the state’s 2012 update added to the energy conservation code mandatory duct testing.” A bill summary from the UNC School of Government lists January 1, 2012 as the effective date for the 2012 codes, with mandatory compliance from March 1, 2012. New duct systems installed outside the conditioned space had to be tested and had to measure below a set limit.
The limit has since tightened. North Carolina’s 2018 energy code, which took effect January 1, 2019 according to the U.S. Department of Energy’s code status page, sets two thresholds for new homes: total duct leakage of no more than 5 CFM25 per 100 square feet of conditioned floor area, and leakage to the outside of no more than 4. Carolina Country reported that the earlier limit had been 6. The same update raised the insulation requirement for ducts in unconditioned spaces from R-6 to R-8, and it requires the test results to be recorded on an energy efficiency certificate for the home.
| When the home or duct system was permitted | Duct leakage test required? | What you can find out | Priority |
| Before the 2012 code took effect | 🔴 No | Probably no test record exists | 🔴 Highest value in testing now |
| Under the 2012 code | 🟡 Yes, to the 2012 limit | Look for an energy certificate or closing documents | 🟡 Worth checking, especially after 10+ years |
| Under the 2018 code (from 2019) | 🟢 Yes, 5 total and 4 to outside | Results should be on the energy certificate | 🟢 Check only if symptoms appear |
| Any age, all ductwork outside the envelope replaced to the boots | 🟢 Yes, per a 2013 state interpretation | Ask the installer for the test results | 🟢 Request the numbers |
| Any age, partial replacement or repair | 🟡 No | Nothing is measured unless you ask | 🟡 Consider testing after the work |
Key Fact: North Carolina’s 2012 energy code was the first to require duct leakage testing for new duct systems outside the conditioned space. In a 2013 interpretation, the state said a test is also required when all ductwork outside the thermal envelope is replaced to the boots, while a partial system installed as part of a replacement, renovation, or addition does not require one.
On February 4, 2013, the North Carolina Department of Insurance’s code staff answered a question that matters to every owner of an older house: does replacing ductwork in an existing building trigger the test? The answer was yes, “in cases where a replacement is so extensive that all the ductwork outside of the thermal envelope (per system) is replaced to the boots.” A partial replacement does not.
In practice, that means many Raleigh homes have had new equipment, new sections of duct, or new flex runs added over the years without anyone ever measuring how much air the system loses.
A large share of the Triangle’s housing went up in the 1990s and 2000s, much of it with ducts in a vented attic, a vented crawl space, or both. Those are the two worst places in a North Carolina house to lose conditioned air.
In the attic, a supply leak sends cooled air into a space that can be far hotter than the outdoors on a July afternoon. That air is simply gone.
In the crawl space, a return leak works in reverse. The system pulls warm, humid air from under the house into the return, and the equipment then has to cool and dry it. In a humid summer that is a large, invisible load.
Building cavities used as ducts are common in homes of this era. Some return air paths run through panned floor joists or framed chases instead of sealed ductwork. Those paths are hard to seal well and often leak at every seam.
| Leak point | Where it shows up | What it does | Priority |
| Plenum-to-air-handler connection | Attic, closet, or crawl space | Large leak right at the equipment, often on the return side | 🔴 Check first |
| Disconnected or slipped flex duct | Attic or crawl space | A room gets little or no air; conditioned air dumps into the space | 🔴 Fix now |
| Boots at floor or ceiling registers | Every register | Leaks into wall, floor, or ceiling cavities | 🟡 Seal during any duct work |
| Panned joist or framed returns | Crawl space or interior walls | Pulls air from the crawl space or wall cavities | 🟡 Evaluate with a test |
| Joints sealed with cloth duct tape | Anywhere | Tape dries out and lets go over time | 🟡 Reseal with mastic or foil tape |
| Uninsulated or torn duct insulation | Attic or crawl space | Heat gain and loss; sweating ducts in summer | 🟡 Re-insulate to current practice |
Attic ducts sit in the hottest part of the house, and the insulation around and above them changes how much heat they pick up. That makes attic insulation that reduces the heat load on attic ductwork part of the same conversation as sealing.
A house built under the 2018 code passed a duct test at completion. That does not guarantee comfort. Tight new homes in the Triangle can hold indoor humidity higher than owners expect during their first year or two. That is a separate problem from leakage, and it is covered in why new construction homes in Raleigh stay humid.
A duct leakage test treats the duct system like a balloon and measures how fast it loses air.
There are two versions. Total leakage measures every leak, including leaks into conditioned rooms. Leakage to the outside is measured with the house itself pressurized at the same time by a blower door, so only air escaping to the attic, crawl space, or outdoors is counted. Leakage to the outside is the part that wastes energy.
A worked example: for a 2,000-square-foot house, the 2018 code’s limits for a new home would be 100 CFM25 total and 80 CFM25 to the outside.
| Result per 100 sq ft (CFM25) | How it compares | What it suggests for an older home | Priority |
| 3 or less | Below the 3 CFM25 target Tideland EMC suggests for a quality job | Ducts are in good shape | 🟢 Maintain |
| 4 or less to outside, 5 or less total | Meets today’s new-home limits | Ducts perform like a new code-built system | 🟢 Good |
| Around 6 total | The pre-2018 limit Carolina Country reported | Typical of a reasonably built system from the 2012 era | 🟡 Seal the worst points |
| Well above 6 total | No code limit applies to an existing home, but the gap is large | Significant leakage; sealing is likely worthwhile | 🔴 Get a sealing estimate |
Existing homes are not held to these limits. They are useful as a yardstick: they tell you how your ducts compare with what the state now requires of a new house.
Duct leakage tests are performed by HERS raters, energy auditors, and some HVAC contractors who own the equipment. When you hire anyone to seal ducts, ask for a test before and after the work. The difference between the two numbers is the most honest measure of what you paid for.
ENERGY STAR lists symptoms that often point to duct problems rather than equipment problems:
In its guidance on replacing equipment, ENERGY STAR adds that humidity problems and excessive dust can also point to leaky ducts or poor insulation rather than to the equipment itself. And it notes that leaky ducts can reduce a heating and cooling system’s efficiency by as much as 20%. A system can run constantly and still leave rooms uncomfortable.
Some of the same symptoms, such as dust, are also used to justify duct cleaning. The difference between “my ducts are dirty” and “my ducts leak” matters, and a plain-language way to tell is in how to know whether your air ducts actually need cleaning.
Key Fact: ENERGY STAR estimates that in a typical house, about 20% to 30% of the air moving through the duct system is lost to leaks, holes, and poorly connected ducts, and that leaky ducts can cut system efficiency by as much as 20%.
The most common duct service sold to Raleigh homeowners is cleaning. The most common duct problem in older Raleigh homes is leakage. They are different jobs.
EPA’s guidance on duct cleaning is direct. Duct cleaning has never been shown to actually prevent health problems, and it should be done as needed rather than on a schedule. EPA lists specific conditions that justify it: substantial visible mold growth, infestation by insects or rodents, or ducts clogged with excessive dust and debris. And EPA says little evidence exists that cleaning only the ducts improves a system’s efficiency.
Sealing works on a different problem. The U.S. Department of Energy recommends sealing duct joints with mastic, butyl tape, foil tape, or another heat-approved tape, and warns against ordinary cloth-backed duct tape, which tends to fail quickly. EPA adds that ducts in attics and crawl spaces should be sealed and insulated to prevent condensation.
| Measure | Effect on leakage and efficiency | What the evidence says | Strength |
| Seal joints with mastic or foil tape | Directly reduces leakage | DOE and ENERGY STAR recommend it | 🟢 Strong |
| Insulate ducts in attic and crawl space | Reduces heat gain, heat loss, and condensation | EPA recommends it for unconditioned spaces | 🟢 Supported |
| Clean coil, blower, and drain pan | May improve efficiency | EPA says some research suggests this | 🟢 Supported |
| Replace ducts that are crushed, brittle, or poorly designed | Resets the system; full replacement outside the envelope triggers a test | Depends on the condition of the old system | 🟡 Case by case |
| Clean the ducts only | Does not seal anything | EPA says little evidence of efficiency gains | 🔴 Weak for efficiency |
When cleaning is warranted in Wake County homes, and what it should include, is covered in when duct cleaning makes sense in Wake County.
When the existing system is too far gone to seal, whether from crushed flex, failed joints, or a layout that never worked, the answer is replacement ductwork installed and sealed as a complete system. If all the ductwork outside the thermal envelope is replaced, the 2013 interpretation means the new system should be tested, and you should ask for the results.
Duke Energy Progress, which serves Raleigh and much of eastern North Carolina, filed a rate case in late 2025 and reached a proposed settlement with the Utilities Commission’s Public Staff in 2026. WRAL reported that under the settlement a typical residential customer using 1,000 kilowatt-hours a month would pay about $9.62 more per month starting January 1, 2027, and about $5.89 more in 2028. The North Carolina Department of Justice calculated the residential increase at about 9.3% over two years, and the Attorney General declined to sign the settlement. Check the Utilities Commission’s final order or your bill insert for the approved figures.
Higher rates do not make leaky ducts leak more. They make each lost cubic foot of conditioned air cost more. A house that loses a fifth or more of its airflow to the attic and crawl space pays the new rate on that loss every month the system runs.
Help with the cost may be available. Duke Energy’s Smart Saver program has offered rebates on duct sealing through participating contractors, and North Carolina’s Energy Saver NC program offers whole-home efficiency rebates scaled to energy savings and household income. Rules and amounts change, so confirm eligibility with the program before planning around it.
| Factor | What is known | Status in October 2026 |
| 🔴 Duke Energy Progress residential rates | Settlement proposes about $9.62 more per month for 1,000 kWh from January 2027 | Proposed; confirm the final order |
| 🟢 Duct leakage in older homes | ENERGY STAR estimates 20% to 30% air loss in a typical house | Measurable with a test |
| 🟡 Duke Energy Smart Saver | Duct sealing rebates through participating contractors | Check current amounts and contractor list |
| 🟡 Energy Saver NC (HOMES) | Whole-home efficiency rebates scaled to savings and income | Confirm eligibility at energysavernc.org |
The broader set of steps that keep a system running efficiently, and how 2026’s cost changes affect repair-or-replace decisions, is laid out in how to make an HVAC system last longer in North Carolina.
A few questions separate a useful duct visit from a sales call.
A fuller guide to comparing companies in the city is in what to look for in a Raleigh air duct cleaning company.
Air Flow Solutions USA inspects ductwork in attics and crawl spaces and gives a written estimate before beginning work. The company is family-owned and fully insured, and its services include duct installation, attic insulation, and crawl space work. Ask it, like any provider, whether leakage will be measured and what the quoted scope covers.
For homeowners in the city, the company’s air duct services for Raleigh homes start with that inspection.
No law requires one for an existing home. But if your Raleigh house was built before North Carolina’s 2012 energy code, its ducts were never required to pass a leakage test, and nobody may ever have measured them. A duct leakage test is the only way to put a number on how much conditioned air the system loses.
With the 2012 North Carolina Energy Conservation Code. A UNC School of Government bill summary lists January 1, 2012 as the effective date and March 1, 2012 as the mandatory compliance date. The requirement applies to new duct systems installed outside the conditioned space. The 2018 code, in effect from January 1, 2019, tightened the limits.
For a new North Carolina home under the 2018 code, total leakage must be no more than 5 CFM25 per 100 square feet of conditioned floor area, and leakage to the outside no more than 4. Those limits do not apply to existing homes, but they are a useful benchmark. Tideland EMC suggests 3 CFM25 per 100 square feet as a target for a quality job.
Sometimes. In a February 2013 interpretation, the state said a test is required when all the ductwork outside the thermal envelope is replaced to the boots, per system. Installing a partial system as part of a replacement, renovation, or addition does not require a test. Ask your contractor which applies to your job.
No. Cleaning removes debris; it does not seal joints or reconnect loose runs. EPA says little evidence exists that cleaning only the ducts improves efficiency. Sealing with mastic or foil tape, and insulating ducts in the attic and crawl space, addresses leakage directly.
ENERGY STAR estimates that a typical house loses about 20% to 30% of the air moving through its ducts to leaks, holes, and poor connections, and that leaky ducts can reduce system efficiency by as much as 20%. Your house may be better or worse. A test tells you which.
Check the year the home was permitted. For a house built under the 2012 code or later, look for the energy efficiency certificate, which records the test results, in your closing documents or near the electrical panel, and ask your local building department for the permit file. For a house built earlier, assume no test was done.
Choose a company that goes into the attic and crawl space, shows you photos, explains how it will measure or document the result, seals with mastic or foil tape, and gives a written scope and price. Air Flow Solutions USA is a family-owned, fully insured company serving the Carolinas that inspects ductwork and provides a written estimate before beginning work. It can be reached at (843) 864-4649.
North Carolina decided in 2012 that a new house’s ducts should be tested before anyone lives in it. Every Raleigh home built before then went through permitting and inspection without that measurement, and nothing since has required one. Many of those houses have ducts in a hot attic and a humid crawl space, connected with materials that have had decades to loosen.
A duct leakage test answers a question most homeowners never think to ask. If the number is good, you know where not to spend money. If it is poor, sealing and insulation are among the measures the evidence supports best, and they matter more as electricity costs rise. Cleaning has its place for the conditions EPA lists. It is not a substitute for ducts that hold air.
Raleigh homeowners can reach Air Flow Solutions USA at (843) 864-4649 or info@airflowsolutionsusa.com, Monday–Saturday 8am–8pm and Sunday 8am–2pm.
This article is for general informational purposes only and does not constitute a code interpretation, an energy audit, or financial advice. Consult qualified professionals and your local building department about your specific home.
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