If you are building a new home or finishing a major renovation in Massachusetts, a blower door test stands between you and your certificate of occupancy. Here is what the test measures, the score your project needs in 2026, what happens on test day, and what to do if a house misses the target — from the RESNET-certified team that runs these tests every day across the state.
What Is Blower Door Testing?
A blower door test measures how airtight a building is by depressurizing it with a calibrated fan mounted in an exterior doorway. As the fan pulls air out of the home, we measure how much air leaks back in through gaps, cracks, and penetrations in the building envelope. The result is expressed as ACH50 — air changes per hour at 50 Pascals of pressure, roughly the force of a 20 mph wind on every surface of the house.
What Score Do You Need in Massachusetts?
| Project type | Max ACH50 |
|---|---|
| New construction (Stretch Code) | 3.0 or lower |
| Remodel / alteration | 5.0 (realistic target for existing assemblies) |
| Addition under 1,000 sq ft | May be exempt — confirm with your building department |
| Passive House / Specialized | 0.6 (whole-building protocol) |
More than 300 Massachusetts municipalities enforce the Stretch Energy Code, which makes the 3.0 ACH50 blower door test mandatory for new residential construction. Blower door results also feed directly into your HERS rating, Mass Save rebate eligibility, and the federal 45L tax credit.
What Happens During the Test
- Preparation — exterior doors and windows closed, interior doors opened, combustion appliances off, dampers closed
- Setup — the calibrated fan is mounted in an exterior door frame with an airtight fabric panel
- Depressurization — the fan holds the home at 50 Pascals below outdoor pressure
- Measurement — airflow through the fan equals the leakage of the envelope; we convert CFM50 to ACH50 using the home’s volume
- Leak hunting — if results are marginal, smoke pencils and infrared imaging pinpoint exactly where the air is getting in
The test itself takes about 30–60 minutes. You get preliminary numbers on the spot and a permit-ready report within 24–48 hours.
What If the House Fails?
A first-test miss is common and fixable. The usual culprits are rim joists, attic hatches, recessed lights, plumbing and wiring penetrations, and unsealed duct boots. Because we test with diagnostic tools running, you leave with a prioritized fail-fix list — seal these specific leaks, in this order, and retest. Most homes that miss by a few tenths pass after a day of targeted air sealing.
How to Prepare for Test Day
- Envelope complete: windows, exterior doors, and weatherstripping installed
- Drywall finished and penetrations sealed (test after air barrier is done, before you run out of schedule)
- HVAC registers installed; fireplace dampers closable
- Power available on site
Frequently Asked Questions
How much does a blower door test cost?
Blower door testing is bundled into our HERS rating packages ($600–$2,500 depending on project size and type). See our full 2026 pricing guide or call for a flat-rate quote.
When in construction should I schedule it?
The final test happens once the envelope is complete — typically just before the certificate of occupancy. Smart builders also book a pre-drywall inspection so leaks get sealed while they are still accessible.
Do I need duct testing too?
If any ductwork runs outside conditioned space, yes — Massachusetts caps duct leakage at 4 CFM25 per 100 sq ft of conditioned floor area. We run both tests in one visit.
Schedule a Blower Door Test
We test across Massachusetts — including Boston, Cambridge, Worcester, and Waltham — with same-day preliminary results. Call (617) 501-6788 or request a quote online.
