Duct Leakage Testing Lexington MA - Quick Facts
Local energy code in Lexington
- As of January 1, 2024, Lexington enforces the Massachusetts Specialized (Opt-In) Energy Code on top of the Stretch Code baseline - IECC Climate Zone 5A.
- The Opt-In code goes further than the Stretch baseline: new fossil-fuel homes must be pre-wired for electrification and include on-site solar where roof space allows.
- New all-electric homes rely on heat pumps for heat and hot water; large fossil-fuel homes over 4,000 sq ft must hit net-zero (HERS 0), and multifamily over 12,000 sq ft must be Passive House.
- Lexington also participates in the Massachusetts Municipal Fossil Fuel-Free Building Demonstration Program - new construction and major renovations must be built fossil-fuel-free (all-electric), a step beyond the Specialized Code.
Duct leakage requirement in Lexington
- Lexington permits under the Massachusetts Stretch Code cap duct leakage at 4 CFM25 per 100 sq ft of conditioned floor area.
- Testing is required unless the entire duct system and air handler sit inside conditioned space; a rough-in test and a final test may both apply.
- Results in 24-48 hours with clear pass/fail documentation, filed with the Lexington building department.
- From $350 for the first ducted system, often bundled with blower door testing and a full HERS rating.
Mass Save rebates for Lexington (2026)
- Duct and blower door results feed the HERS rating that unlocks Mass Save all-electric incentives: $7,500 to $25,000 per new single-family home and $1,000 to $3,750 per multifamily unit.
- Incentives require a Mass Save-approved, RESNET-certified HERS rater.
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Duct Leakage Testing Lexington MA
Certified duct leakage testing for Lexington, measured with a calibrated duct blaster and documented for your permit and HERS rating.
Duct Leakage Requirements in Lexington
Lexington enforces the Massachusetts Specialized (Opt-In) Code, which uses the same duct leakage limit as the Stretch Code: 4.0 CFM25 per 100 square feet of total leakage, or 3.0 at rough-in before the air handler is installed. Our raters measure your ductwork in CFM25 and document a clear pass against the 4.0 CFM25 per 100 sq ft limit.
| Project / code tier | Duct leakage limit | What is tested |
|---|---|---|
| Base energy code | 4.0 CFM25 / 100 sq ft | Total leakage (ducts outside conditioned space) |
| Stretch Code | 4 CFM25 / 100 sq ft (total) | Total leakage (leakage to outside is not a code option) |
| Rough-in test, air handler not installed | 3.0 CFM25 / 100 sq ft | Total leakage (Stretch and Specialized) |
| Ducts fully inside envelope | 8.0 CFM25 / 100 sq ft (test still required) | Air handler + ducts in conditioned space |
IECC Duct Leakage Thresholds Reference
Beyond the Massachusetts tier that applies in Lexington, these are the federal IECC duct-leakage limits across code editions. All values are CFM at 25 Pascals (CFM25) per 100 sq ft of conditioned floor area (CFA) unless noted.
2009 IECC
| Test stage | Measurement | Leakage limit |
|---|---|---|
| Postconstruction Leakage Test | Duct Leakage to Outdoors | ≤ 8 CFM25 / 100 sq ft CFA |
| Rough-in with AHU | Total Duct Leakage | ≤ 6 CFM25 / 100 sq ft CFA |
| Rough-in without AHU | Total Duct Leakage | ≤ 4 CFM25 / 100 sq ft CFA |
2012, 2015, 2018 & 2021 IECC — Prescriptive Paths
| Test stage | Measurement | Leakage limit |
|---|---|---|
| Postconstruction Leakage Test | Total Duct Leakage | ≤ 4 CFM25 / 100 sq ft CFA |
| Rough-in with AHU | Total Duct Leakage | ≤ 4 CFM25 / 100 sq ft CFA |
| Rough-in without AHU | Total Duct Leakage | ≤ 3 CFM25 / 100 sq ft CFA |
2015 & 2018 IECC — Performance Path (Cost Compliance)
Leakage testing is required unless all ducts and air handlers are located entirely within the thermal envelope. There is no pass/fail threshold for duct leakage on the performance path.
2024 IECC — Prescriptive Path
| Conditioned floor area | Condition at test | Total leakage limit |
|---|---|---|
| >1,000 sq ft CFA | Space-conditioning equipment not installed | < 3 return grilles: ≤ 3 CFM · 3+ return grilles: ≤ 4 CFM |
| >1,000 sq ft CFA | All components installed | < 3 return grilles: ≤ 4 CFM · 3+ return grilles: ≤ 6 CFM |
| >1,000 sq ft CFA | Equipment not installed, ducts entirely in conditioned space | < 3 return grilles: ≤ 6 CFM · 3+ return grilles: ≤ 8 CFM |
| >1,000 sq ft CFA | All components entirely in conditioned space | < 3 return grilles: ≤ 8 CFM · 3+ return grilles: ≤ 12 CFM |
| ≤1,000 sq ft CFA | Equipment not installed | ≤ 30 CFM |
| ≤1,000 sq ft CFA | All components installed | ≤ 40 CFM |
| ≤1,000 sq ft CFA | Equipment not installed, ductwork entirely in conditioned space | ≤ 60 CFM |
| ≤1,000 sq ft CFA | All components entirely in conditioned space | ≤ 80 CFM |
How Duct Leakage Testing Works in Lexington
A duct blaster seals off your HVAC system and pressurizes it to 25 Pascals. The airflow needed to hold that pressure is your leakage rate in CFM25 — the lower the number, the tighter the ducts.
Common Sources of Duct Leakage We Check in Lexington
Most duct leakage comes from a short list of predictable weak points. Knowing where to look is what turns a CFM25 number into a fixable list of locations.
Boot & register connections
The joint where a duct boot meets the drywall is the single most common leak point — often left unsealed behind the register grille.
Plenum & air-handler seams
Sheet-metal plenums and the cabinet of the air handler leak at seams and access panels unless mastic-sealed.
Disconnected flex runs
Flexible ducts can pull loose at collars or get crushed above insulation, dumping conditioned air into the attic.
Panned-joist returns
Return cavities framed from floor joists or wall studs are notoriously leaky and can draw in unconditioned air.
Building-cavity returns
Using framing cavities as return ducts pulls air from attics, garages, or crawlspaces instead of living space.
Trunk-line joints
Long supply trunks flex and separate at joints over time, especially where they were only taped rather than sealed with mastic.
Why Tight Ducts Keep Heat In Your Lexington Home
Ductwork is the delivery system for every dollar of heating and cooling in a Lexington home. If it leaks, that conditioned air is lost before it ever reaches a living space.
Once the ducts test tight, the heat you pay for stays in the living space, the system cycles less, and utility bills settle down.
What Your Lexington Duct Test Report Includes
You get a document your building department and HERS software will accept the first time — not just a number.
- ✓The test method used (rough-in or post-construction) per ANSI/RESNET/ICC 380
- ✓Documentation formatted for your HERS rating and building-permit file
- ✓A punch list of leak locations if a re-seal and retest is needed
- ✓Measured total duct leakage in CFM at 25 Pascals (CFM25)
- ✓Leakage normalized per 100 sq ft of conditioned floor area
- ✓Clear pass/fail against the 4.0 CFM25 limit that applies in Lexington
Best Fit for Projects Like
- Additions in Lexington where new HVAC ducts must comply with Section R403
- Builders who need a fast, permit-ready duct test scheduled around drywall
- Lexington new-construction homes needing a duct test to complete the HERS rating
- Multi-unit conversions where each system needs documented duct leakage results
- Homes switching to a heat pump where duct tightness protects the new system's output
Duct Leakage Testing Lexington MA Facts
- A duct leakage tester, or duct blaster, pairs a calibrated fan with a precise pressure sensor to quantify how leaky the ducts are.
- The U.S. Department of Energy estimates a typical home loses 20 to 30 percent of its conditioned air through duct leaks.
- The 2025 Massachusetts Technical Guidance requires HVAC ducts newly installed as part of an addition to comply with Section R403.
- A duct air-leakage test is not required where the ducts and air handler sit entirely within the conditioned space.
Trusted for Duct Leakage Testing Lexington MA
Our Massachusetts Service Locations
Serving clients from our Massachusetts locations in Everett, Somerville, and Framingham.
Everett Location
371 Main St
Everett, MA 02149
Somerville Location
519 Broadway
Somerville, MA 02145
Framingham Location
68 South St
Framingham, MA 01702
Duct Leakage Testing for Lexington Homes
Lexington is on the Specialized (Opt-In) Code, in effect since January 1, 2024, and is one of the towns in the state's Fossil Fuel Free Building Demonstration Program. Since March 21, 2024, Lexington's bylaw has required new construction, major renovations and large additions to be built without fossil fuel equipment unless the Building Commissioner grants a waiver. New homes are heated electrically, and when the heat pump is ducted, duct tightness matters even more.
The test
Every ducted system gets a total duct leakage test. The limit is 4.0 CFM25 per 100 sq ft of conditioned floor area, or 8.0 CFM25 per 100 sq ft when all ductwork and the air handler are in conditioned space; the test is still required in that case. Testing at rough-in, before drywall, finds leaks while they are easy to reach. The final test gives the number for the HERS rating.
Lexington houses
Most of Lexington's housing is single-family, 85% per the town's 2014 Housing Production Plan, and that plan found 78% of new single-family homes built from 2000 to 2011 replaced teardowns. For additions and renovations on older houses, new ducts frequently pass through attics and basements. The leaks we chase: register boots open to the wall or ceiling cavity, air handler panels, flex connections and unsealed trunk seams.
Why it matters for a heat pump
A heat pump delivers air at lower temperatures than a furnace, so a leak is felt as a slow-to-heat room, and leakage also raises the HERS score. Electric service is Eversource and gas is National Grid, both Mass Save sponsors.
Lexington's Building Office takes permits through its OpenGov ViewPoint Cloud system. Building inspections are requested by phone and can be scheduled for the following business day. Our nearest office is in Somerville at 519 Broadway.
Real duct leakage tests by HEEC for Lexington projects
These are photos from Home Energy Efficiency Consultants duct leakage testing jobs in Massachusetts — the same equipment and setup our certified raters bring to Lexington homes.
Duct Leakage Testing Lexington MA FAQ
Duct Leakage Test Requirements for Lexington Projects
Lexington is one of the 60 Massachusetts communities on the Specialized (Opt-In) Code. New homes there are built on the same 225 CMR 22.00 testing requirements below, plus net-zero-ready provisions.
| Test | Limit (CFM25 per 100 sq ft of conditioned floor area) | Notes |
|---|---|---|
| Rough-in, air handler installed | 4.0 total leakage | ANSI/RESNET/ICC 380 or ASTM E1554 |
| Rough-in, air handler not installed | 3.0 total leakage | Air handler added later |
| Post-construction | 4.0 total leakage | Final test with the system complete |
| Ducts and air handler entirely inside the thermal envelope | 8.0 total leakage | Test is still required |
| Ventilation-only ducts | Exempt | Only if not tied into heating or cooling ducts |
Massachusetts measures total duct leakage; "leakage to outside" is not a code option. Under the Massachusetts amendment to R403.3.5, the test must be done by a HERS Rater, HERS Rating Field Inspector or BPI Certified Professional, with a signed report to the Lexington building department. Mechanical ventilation airflow must also be tested and verified by a HERS Rater under R403.6.3.
Sources: 225 CMR 22.00 (2025 edition) and the 2021 IECC sections listed. Lexington is in Middlesex County, served from our Somerville (519 Broadway) office.
Duct Leakage Questions from Lexington Builders
What is the duct leakage limit for a new home in Lexington?
4.0 CFM25 of total leakage per 100 square feet of conditioned floor area, at rough-in or after construction. If the air handler is not installed at rough-in the limit is 3.0, and if every duct and the air handler are inside the thermal envelope the limit is 8.0.
Can leakage to outside be used instead of total leakage?
No. The Massachusetts code (225 CMR 22.00 R403.3.5) measures total duct leakage. Leakage-to-outside tests are used by some programs, but not for code compliance here.
Who can perform the duct test in Massachusetts?
A HERS Rater, a HERS Rating Field Inspector or a BPI Certified Professional, under the Massachusetts amendment to R403.3.5. The tester signs a written report for the code official.
Is a duct test required if all ducts are inside conditioned space?
Yes. Massachusetts follows the 2021 IECC, which still requires the test but allows up to 8.0 CFM25 per 100 square feet when the ducts and air handler are entirely inside the thermal envelope.
Rough-in or final: which test is better?
A rough-in test catches leaks while every joint is still reachable, so fixes are cheap. A post-construction test confirms the finished system. Many builders do both to avoid surprises at final.
How much does duct leakage testing cost in Lexington?
Our duct testing is $350 for the first ducted system and $250 for each additional system at the same address. It can be done in the same visit as the blower door test and HERS inspection.
Related: Blower door testing in Lexington · HERS rating in Lexington · Stretch Code help in Lexington
Get Started With Duct Leakage Testing Lexington MA
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HERS Ratings Across Lexington and Nearby Communities
Home Energy Efficiency Consultants rates new homes, additions, and major renovations throughout Lexington — including Lexington Center, East Lexington, and Munroe. Every Lexington project is filed with the Town of Lexington Building Department, and we handle the energy model, blower door and duct leakage testing, and the compliance paperwork from start to finish.
We also serve the communities right around Lexington, including Arlington, Bedford, Burlington, Winchester, and Lincoln. Our Somerville office at 519 Broadway is the closest of our four Massachusetts locations — see our Somerville office or call (617) 501-6788 to get a Lexington rating on the schedule.
Lexington Specialized Energy Code — HERS Index Targets
Lexington enforces the Massachusetts Specialized (Opt-In) Energy Code. The required HERS score depends on fuel type and project scope — a lower index is stricter. As a fossil-fuel-free community, new construction in Lexington must be built all-electric, so the all-electric columns apply.
| Project type | Mixed-fuel | Mixed-fuel + solar | All-electric | All-electric + solar |
|---|---|---|---|---|
| New construction | HERS 42 | 42 | 45 | 45 |
| New construction — embodied-carbon credit | 45 | 45 | 48 | 48 |
| Accessory dwelling unit (ADU) | 52 | 55 | 55 | 58 |
| Major alteration / renovation / change of use | 65 | 70 | 70 | 75 |
A HERS rating is triggered by new construction, additions over 1,000 sq ft (or more than 100% of the existing conditioned area), and Level 3 alterations over 1,000 sq ft affecting more than 50% of the home. New homes must also pass a blower-door test at 3.0 ACH50 and include electrification-ready wiring for heat pumps, EV charging, and solar. We model your Lexington project up front so you know the exact target and the fastest path to hit it — call (617) 501-6788.
