Your blower door report just landed with an ACH50 number on it, and nobody told you whether that number is good or bad for a house like yours. There is no single passing score. What counts as tight depends heavily on when your house was framed, and a number that would be excellent for a 1965 ranch in Freehold Township would be a failing grade on a brand new build. Novus Mechanical runs this test across Monmouth County and reads the result against your house's actual era, not a chart built for new construction. Lower is better, generally, but there is also a point where tighter stops helping and starts creating problems of its own.
A blower door is a calibrated fan that seals into an exterior doorway and pulls the house down to 50 pascals of pressure, roughly the suction of a stiff wind hitting every side of the house at once. Two numbers come out of that pull. CFM50 is the raw airflow, the cubic feet of air per minute the house is losing at that pressure. ACH50, air changes per hour at 50 pascals, divides that same leakage by the volume of the house, so a small ranch and a big colonial can be compared fairly. We measure both with Retrotec equipment.
CFM50 tells you how much a specific fan or duct system has to fight. ACH50 is the number worth remembering, because it is the one that scales, and it is the one every era comparison in this guide uses.
There is no universal target, but there is a realistic range for each era of construction in this county, based on what typically shows up before any sealing work has been done. Treat these as starting points to judge your result against, not a promise about your specific house.
| Home era | Typical ACH50 before sealing work | What's usually driving it |
|---|---|---|
| 1950s to 1960s ranch | 15 to 25 or higher | Balloon-framed walls open straight to the attic, no house wrap, one furnace swap over 60 years but never a duct or envelope change |
| 1970s split level | 12 to 20 | Multiple roof lines and knee walls that back straight onto unconditioned attic pockets |
| 1980s colonial | 10 to 18 | Better windows than the ranches around it, but still no dedicated air sealing anywhere in the shell |
| 2000s build | 7 to 12 | Built to the energy code of its decade, which did not require a blower door test to close the permit |
| Current new build | 3 or tighter, and it's checked | New Jersey's current energy code requires the number and verifies it with a mandatory test |
A 1970s split level testing at 16 ACH50 is not a bad result. It is close to normal for the type. The same number on a house built last year would mean something went wrong.
New Jersey adopted the 2021 IECC as its residential energy code, and that code sets a specific air leakage target for new single-family construction, checked with a mandatory blower door test before the permit closes. That number is a new-construction requirement, not a grade applied to a house that was already standing when the code took effect. Nobody is failing a 1978 split level against a rule written for a house being framed this year.
If you are pulling a permit for an addition or a gut renovation, the code may reach into that specific scope of work, and the exact figure depends on the cycle in effect when the permit is filed. Your municipal construction official has the number that applies to your project. For everyone else, the honest read of an older house's score is simply how it compares to homes of its own era, and how far it has to travel to get comfortable and efficient.
Yes, and this is the part most sealing pitches skip. As a house gets tighter, it stops getting enough fresh air from ordinary leakage, and the industry ventilation standard, ASHRAE 62.2, expects mechanical ventilation to take over once a home approaches roughly 3 ACH50. Below that, you're not relying on random gaps to trade stale air for fresh air anymore. Something has to do that job on purpose, whether that's a bath fan on a timer or a dedicated fresh-air system.
Sealing also changes how combustion equipment behaves. A natural draft water heater or an older furnace on a standing pilot depends on a certain amount of house leakage to draft properly and vent exhaust outside. Tighten the house without checking that, and you can end up with a water heater that spills combustion gases into the basement instead of up the flue. Any sealing job on a house with atmospheric-vent equipment should include a combustion safety test, not skip straight to caulk and foam.
Monmouth County sits in EPA Radon Zone 1, the agency's highest risk category, and that matters the moment you start sealing a basement. Radon gas moves up out of the soil through the slab and foundation walls, and a leakier house dilutes that gas with more outside air, whether or not that was ever the plan.
Seal the basement tighter without addressing radon, and the concentration inside can climb, since there's less air exchange doing the diluting. The fix is not to leave the basement leaky on purpose. It's to test for radon before or alongside the sealing work, and if the number comes back high, pair the air sealing with a mitigation system rather than treating them as two unrelated projects. A blower door test tells us how the house breathes, and that's exactly the information a radon mitigation plan needs too.
We run blower door testing across Freehold, Marlboro, Manalapan, Colts Neck, Holmdel, Howell, and the surrounding parts of Monmouth County. Residential homes only. This test feeds directly into a full home energy audit when you want the whole picture, and it's also the number behind an accurate Manual J load calculation if you're pricing new equipment. See what the test actually finds room by room, or read the case for sealing before insulating if you're planning both.
Technicians are on site Monday through Friday, 8 AM to 6 PM, and the phone is answered any time so you can get on the schedule. A blower door test starts at $350. Call and we'll walk you through what your number means for a house like yours before we schedule anything.
There is no universal number, only a realistic range for each era. A 1950s or 1960s ranch commonly tests at 15 to 25 ACH50 or higher before any sealing work, a 1970s split level at 12 to 20, and a 1980s colonial at 10 to 18. A 2000s build usually lands around 7 to 12. A current new build in New Jersey has to hit roughly 3 ACH50 or tighter, verified with a mandatory blower door test. Judge your result against your house's own era, not against new construction.
For new construction built with air sealing in mind, not hard. The New Jersey requirement is 3 ACH50, and builders who detail the air barrier as they go clear it routinely. It gets hard when sealing is treated as a final step, because by then the penetrations are buried behind drywall. Existing homes are a different conversation: there is no passing score for a house that already stands, only a number to improve on.
Start with ACH50, the number of times the house's full volume of air leaks out per hour at the test pressure, and compare it to the range for your home's era rather than to new construction. Then look at CFM50, the raw airflow, which tells you the size of the hole you are dealing with instead of how it compares to house volume. The most useful part is not the score at all: it is the list of where the leakage was found, because that is the part you can act on.
It depends entirely on house size, which is exactly why ACH50 exists. As a rough anchor, a 2,000 square foot house with 8 foot ceilings holds about 16,000 cubic feet, so 3 ACH50 works out to roughly 800 CFM50, while a leaky older house of the same size can read 3,000 CFM50 or more. Compare CFM50 only between houses of similar volume. Otherwise use ACH50.
We measure your home, explain what we find, and hand you one clear price. Book a consultation in Freehold or Monmouth County.
Updated August 2026 by Novus Mechanical, Freehold, NJ
