Blower Door Testing Shrewsbury MA - Quick Facts
Local energy code in Shrewsbury
- Shrewsbury enforces the Massachusetts Stretch Energy Code for new construction and major renovations. IECC Climate Zone 5A.
- Massachusetts has three energy-code levels - base (2021 IECC), Stretch, and Specialized (Opt-In) - and Shrewsbury is on the Stretch Code.
Blower door requirement in Shrewsbury
- New homes in Shrewsbury must test at 3.0 ACH50 or tighter under the Massachusetts Stretch Code.
- Air-leakage testing is mandatory, measured with a calibrated blower-door fan to the RESNET / ASTM protocol - there is no inspection-only substitute for the result.
- Companion duct leakage limit: 4.0 CFM25 per 100 sq ft of conditioned floor area total leakage (8.0 when all ducts are inside conditioned space - the test is still required).
- Same-day preliminary results; final report in 24-48 hours, filed with the Shrewsbury building department.
2026 Mass Save incentives in Shrewsbury
- A tight result unlocks Mass Save all-electric incentives ($7,500 to $25,000 per new single-family home); an all-electric renovation testing at 3.0 ACH50 or better reaches the Level 2 tier, up to $30,000.
- Incentives require a Mass Save-approved, RESNET-certified HERS rater.
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Blower Door Testing Shrewsbury MA
Certified blower door testing in Shrewsbury - we measure your home's air-tightness in ACH50, pinpoint leaks, and document a passing result for your building permit.
Air-tightness at a glance
Blower Door Testing Shrewsbury MA
A blower door test is the code-required way to prove how airtight a home in Shrewsbury really is. A calibrated fan depressurizes the house to 50 Pascals so we can measure exactly how much air leaks through the envelope, reported as air changes per hour (ACH50). New construction must reach 3.0 ACH50 or lower, and no home on any compliance path may exceed 5.0 ACH50 (IECC 2021 R402.4.1.2).
| Project type | Max ACH50 | Notes |
|---|---|---|
| New construction | 3.0 or lower | Mandatory blower-door test under R402.4.1.2 |
| Maximum on any compliance path | 5.0 | Code cap under IECC 2021 R402.4.1.2 |
| Addition < 1,000 sq ft | Exempt* | May be exempt from testing (R502.3.1) |
| Passive House (PHI; Phius uses 0.06 CFM50/sq ft) | 0.6 | Whole-building test, Phius/PHI protocol |
*Confirm with your local building department. Requirements per the 2025 MA Stretch Energy Code Technical Guidance.
How Blower Door Testing Works in Shrewsbury
The fan mounts in an exterior doorway and holds the home at a fixed 50-Pascal pressure difference - about what a 20 mph wind would exert. The airflow required to maintain that pressure, in CFM, converts to ACH50 using the home's conditioned volume.
The code converts the result to Q50 (CFM at 50 Pa) with Q50 = (Volume × ACH50) ÷ 60. A 2,700 sq ft home at 2 ACH50 works out to roughly 810 CFM50.
Keeping Heat In During Shrewsbury Cold Spells
During a New England cold snap the stack effect goes to work: warm indoor air rises and slips out near the top of the house, and that pulls cold outdoor air in through gaps down low. The colder it gets, the harder this effect pushes - so a leaky home loses the most heat exactly when it can least afford to.
A tight, tested envelope shrinks the infiltration share of your heating load. That lets the equipment keep up during cold spells, holds rooms at a steadier temperature between cycles, and often lets a designer right-size the heating system rather than oversizing it to cover leakage.
Lower heating load
Less infiltration means a smaller winter heat-loss load and equipment that can keep up.
Retain paid-for heat
Warm air stays in the living space instead of escaping out the top of the house.
Steadier comfort
Fewer cold-floor drafts and a temperature that holds between heating cycles.
Where Shrewsbury Homes Leak Air
During depressurization the leaks are exaggerated, making them easy to find. In Worcester County's older housing stock the usual suspects are rim joists, top plates, attic hatches, recessed lights, and penetrations for plumbing and wiring. Coastal and exposed sites feel wind-driven infiltration most, so a tight, verified envelope pays back quickly here.
Best Fit for Projects Like
- Multi-family and townhouse units
- Additions over 1,000 sq ft that trigger testing
- New single-family homes needing a code compliance test
- Mass Save incentive and rebate projects
- Drafty existing homes seeking targeted air sealing
Blower Door Testing Shrewsbury MA Facts
The reference scale
For perspective, a very leaky older home can exceed 11 ACH50, current code sits at 3.0 for new builds, and certified Passive House projects reach 0.2 to 0.6 ACH50.
Right-sizing equipment
A verified-tight envelope lets a designer right-size the furnace, boiler, or heat pump instead of oversizing for leakage - lowering both equipment cost and running cost.
Comfort, not just code
Beyond passing code, a tight envelope removes drafts, stabilizes room-to-room temperatures, and reduces the dust and outdoor pollen pulled in through gaps.
Documentation for permits
Passing results are recorded on a RESNET/HERS-style form that becomes part of the building permit and certificate of occupancy file.
Trusted for Blower Door Testing Shrewsbury MA
Dominic did an excellent job guiding me through the HERS rating process, and it's clear he genuinely had my best interests in mind.
Knowledgeable and professional. Highly recommend them if you want a thorough efficiency assessment.
When I was going to pull my building permit I was confused about documentation to meet the Massachusetts stretch energy code, but Home Energy was extremely helpful in explaining the HERS rating process and helping me apply for Mass Save rebates.
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
Blower Door Testing in Shrewsbury: What to Expect
Shrewsbury has been on the Stretch Code since January 1, 2018 according to the state's adoption list and has not adopted the Specialized (Opt-In) Code. New homes in town must pass a blower door test at 3.0 ACH50 or lower when construction is finished, before the certificate of occupancy. Passive House and Phius homes are held to much tighter limits.
Working with the Building Inspector's office
Shrewsbury's Building Inspector's office (508-841-8512) keeps short public hours, by appointment only: 8 to 9 a.m. and 3 to 4:30 p.m. Monday through Thursday, and 8 to 9 a.m. on Friday. Permits are applied for online. Electric service comes from the town's municipal utility, SELCO, which requires a work request number for electrical permits. Plan the blower door test before you call for the final so the report is ready.
Mostly single-family homes
A 2019 town housing plan (using ACS 2012-2016 data) found about 64% of Shrewsbury's homes are single-family detached, with a median year built of 1974. In new single-family houses the leaks we find most are at rim joists, attic hatches, recessed lights, and plumbing and wiring penetrations. Older houses that are opened up for a rebuild add sill plates and top plates to the list, which is why a pre-drywall check is worth booking.
Prep and retests
- Windows and exterior doors closed, interior doors open.
- Heating, cooling and ventilation off.
- Water poured into every drain trap.
- Exhaust and ventilation openings sealed only where the test protocol allows.
If the house fails, we keep the fan running, find the leaks, and retest after sealing. Shrewsbury is served from our Marlborough office at 272 Lincoln St C1.
Real blower door tests by HEEC for Shrewsbury projects
These are photos from Home Energy Efficiency Consultants blower door testing jobs in Massachusetts — the same equipment and setup our certified raters bring to Shrewsbury homes.
FAQ About Blower Door Testing Shrewsbury MA
What documentation do I receive?
You receive the measured ACH50 result on a RESNET/HERS-style report suitable for the building department, plus notes on any sealing performed.
What ACH50 does new construction need to pass?
New residential construction in Massachusetts must measure 3.0 ACH50 or lower. Many high-performance homes come in well below that figure.
How long does a blower door test take?
For a typical single-family home the test itself usually takes well under an hour once the fan is set up and the home is prepared.
How is ACH50 converted to CFM?
The code uses Q50 = (conditioned volume x ACH50) / 60. For example, a 2,700 sq ft home with 9 ft ceilings at 2 ACH50 equals about 810 CFM50.
Does a tighter house need mechanical ventilation?
Yes. A tight home relies on balanced mechanical ventilation for fresh air, and the code sizes that ventilation (R403.6 / ASHRAE 62.2) using your verified blower-door rate.
What is a blower door test?
It is a diagnostic that measures how airtight a building is. A calibrated fan mounted in a doorway pressurizes or depressurizes the home to 50 Pascals and measures the airflow needed to hold that pressure, which is reported as ACH50.
What are the Shrewsbury Building Inspector's office hours?
Appointments are required. The office is open 8:00 to 9:00 a.m. and 3:00 to 4:30 p.m. Monday through Thursday, and 8:00 to 9:00 a.m. on Friday. The phone number is 508-841-8512.
Do Shrewsbury electrical permits need anything from SELCO?
Yes. SELCO, Shrewsbury's municipal utility, says electrical permits need a SELCO work request number, which is obtained through the town's online portal.
Blower Door Test Requirements for Shrewsbury Projects
Shrewsbury is not on the Specialized Code list. It has been on the Massachusetts Stretch Code (225 CMR 22.00) since January 1, 2018, according to the state's adoption list. The testing requirements below come from 225 CMR 22.00 and the 2021 IECC it amends.
| Requirement | Limit | Source |
|---|---|---|
| New home, prescriptive path | 3.0 ACH50 or lower | IECC 2021 R402.4.1.3 (Climate Zone 5, all of Massachusetts) |
| Maximum on any compliance path | 5.0 ACH50 or 0.28 CFM50 per sq ft of enclosure | IECC 2021 R402.4.1.2 |
| Attached homes and apartments tested unit by unit | 0.30 CFM50 per sq ft of unit enclosure (alternative) | IECC 2021 R402.4.1.2 exception |
| Mass Save ENERGY STAR tier | 1.5 ACH50 or lower | Mass Save new construction program |
| Passive House (PHI) | 0.6 ACH50 or lower | Passive House Institute |
| Passive House (Phius) | 0.06 CFM50 per sq ft of enclosure (0.08 for non-combustible 5+ stories) | Phius 2024 Certification Guidebook |
How the house is set up for the test
- Exterior windows and doors closed, with no sealing beyond normal weatherstripping
- Dampers closed but not taped, and interior doors open
- Exterior ventilation openings sealed, heating and cooling turned off, supply and return registers open
- Tested at 50 Pascals per ANSI/RESNET/ICC 380, ASTM E779 or ASTM E1827, with a signed report for the Shrewsbury building department
Sources: 225 CMR 22.00 (2025 edition) and the 2021 IECC sections listed. Shrewsbury is in Worcester County, served from our Marlborough (272 Lincoln St) office.
Blower Door Questions from Shrewsbury Builders
What blower door number does a new home in Shrewsbury need?
On the prescriptive path the 2021 IECC requires 3.0 ACH50 or lower in Massachusetts, and no home on any path may exceed 5.0 ACH50. Homes on the HERS path are tested the same way, and the result goes into the HERS model, so a tighter house earns a lower HERS score.
What is ACH50?
Air changes per hour at 50 Pascals: how many times the home's air volume leaks out each hour while a blower door holds the house at 50 Pa. ACH50 = CFM50 × 60 ÷ conditioned volume.
How are townhouses and apartments tested?
Each dwelling unit can be tested on its own and meet 0.30 CFM50 per square foot of the unit's enclosure, which counts walls, floor and ceiling shared with neighbors. Large buildings may also get a whole-building test.
What gets taped or closed during the test?
Windows and exterior doors are closed, dampers are closed but not sealed, and exterior ventilation openings such as bath fan and ERV/HRV terminations are sealed. Interior doors stay open and the heating and cooling system is off.
When should the blower door test happen?
The code test happens at the end of construction. We recommend a pre-drywall test once the air barrier is complete, when leaks are cheap to find and fix, so the final test is a formality.
How much does blower door testing cost in Shrewsbury?
Pricing depends on the size of the building and the number of units. Send your plans or address and we will quote the test, or bundle it with your HERS rating and duct test in one visit.
Related: Duct leakage testing in Shrewsbury · HERS rating in Shrewsbury · Stretch Code help in Shrewsbury
Get Started With Blower Door Testing Shrewsbury MA
Book a certified blower door test and get a permit-ready air-tightness report. Call 617-501-6788.
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HERS Ratings Across Shrewsbury and Nearby Communities
Home Energy Efficiency Consultants rates new homes, additions, and major renovations throughout Shrewsbury — including Shrewsbury Center, Edgemere, and White City. Every Shrewsbury project is filed with the Town of Shrewsbury 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 Shrewsbury, including Worcester, Westborough, Northborough, Grafton, and Boylston. Our Marlborough office at 272 Lincoln St is the closest of our four Massachusetts locations — see our Marlborough office or call (617) 501-6788 to get a Shrewsbury rating on the schedule.
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