Marion County Blower Door Requirements: ACH50 Limits, Florida 2023 Code, and What Permit Reviewers Check

Florida new construction has required blower door testing on every new residential build since 2020, and the 2023 Florida Building Code, Energy Conservation chapter tightened the requirements further. For Marion County projects — including Ocala, Belleview, Dunnellon, and the rest of the county — the blower door test is one of the final pre-occupancy checks before the building department issues a certificate of occupancy.

This article covers the specific code requirements, how the test is performed, what limit your project has to hit, and what Marion County reviewers actually check. For the broader picture of all testing required for new construction, see our new construction energy testing guide for Marion County.

What a Blower Door Test Measures

A blower door is a calibrated fan that gets installed in an exterior doorway. It pressurizes (or depressurizes) the house to a standard reference pressure — 50 Pascals — and measures how much air the fan has to move to maintain that pressure. The result is reported in either:

• CFM50 — cubic feet per minute of airflow at 50 Pa
• ACH50 — air changes per hour at 50 Pa (CFM50 × 60 ÷ house volume)

ACH50 is the more useful metric because it normalizes for house size. A 5,000 sq ft home and an 1,800 sq ft home can be compared on the same scale.

The Florida Energy Code uses ACH50 as the compliance metric. For the broader technical detail on both blower door and duct leakage testing, see our envelope leakage testing guide.

The Florida Code Limit for New Construction

Florida Building Code, Energy Conservation 8th Edition (2023), Section R402.4.1.2 sets three numbers that matter for Climate Zone 2 (all of Marion County):

≤7 ACH50 — the prescriptive testing maximum for Climate Zones 1 and 2.

≤5.0 ACH50 — the absolute ceiling for any dwelling unit under any compliance path. This is the number builders actually need to hit. Even projects using the performance path or ERI path cannot exceed 5.0 ACH50.

<3 ACH50 — when a unit tests below this threshold, FBC-EC R403.6.1 requires the building department to verify that whole-house mechanical ventilation has been installed per Section M1507.3 of the Florida Building Code, Residential.

In practice, 5.0 ACH50 is the working target across the industry. Test under it and you pass; test under 3 and you need verified mechanical ventilation.

For comparison:

• Older Florida homes built before the 2010 code changes often test at 8–15 ACH50 (very leaky)
• Code-compliant new construction targets ≤5.0 ACH50 (Florida code ceiling)
• High-performance new construction can hit 2.0–4.0 ACH50 (very tight)
• Below 3 ACH50 triggers the mechanical ventilation verification requirement

Who Has to Test and When

The 2023 Florida Energy Code requires blower door testing for all new residential construction, including:

• Single-family detached homes
• Townhouses
• Duplexes
• Manufactured / modular homes (in many cases)
• Substantial additions (>50% of original conditioned area, in many cases)

The test is typically performed after drywall and before final inspection — usually when the house is at the trim-out / paint-ready stage. Testing too early (before drywall) gives an inaccurate result because too many penetrations are still open. Testing too late doesn’t help if the result is over limit and you have to find and fix leaks.

How the Test Is Performed

A standard blower door test in Marion County follows ANSI/RESNET/ICC 380 procedures:

1. House preparation. All exterior doors and windows closed. Interior doors open. HVAC system off. Fireplace dampers closed. Range hoods and bath fans off. Bath fan and dryer ducts taped over (per protocol).

2. Blower door installation. The blower door is set up in an exterior doorway with a calibrated fan and a digital pressure gauge.

3. Pre-test conditions. Outdoor temperature, wind speed, and indoor temperature are recorded. Test cannot be performed in very high winds or in extreme temperature differentials without correction factors.

4. Depressurization test. The fan pulls air out of the house, creating negative pressure inside. Fan speed is adjusted until the pressure gauge reads exactly -50 Pa. The fan’s CFM at that pressure is the CFM50 result.

5. Conversion to ACH50. CFM50 × 60 ÷ house conditioned volume = ACH50.

6. Documentation. Result is recorded, signed by the technician, and attached to the project file.

A single test takes about 30–60 minutes once the house is prepared. If the result is above 5.0 ACH50, the technician usually performs a leak-finding pass using smoke pencils or infrared thermal imaging to identify where the major air leakage is happening.

What Causes a Marion County Home to Fail

The most common failure patterns in Ocala new construction:

Penetrations not sealed. Plumbing stacks, electrical chases, HVAC line sets, exhaust ducts. Each one is a hole through the envelope. If they’re not sealed with the appropriate gasket, foam, or caulk, they leak.

Top plate gap. Where the wall meets the ceiling, there’s typically a small gap between the top plate and the drywall. In conditioned-attic builds this isn’t an issue, but in vented-attic builds the gap leaks directly to the attic.

Recessed lighting (can lights). Unless rated IC-AT (insulation contact, air tight), can lights are major leak points. New construction increasingly uses IC-AT cans, but older builds may have legacy fixtures.

Attic access panels. Pull-down stairs and attic hatches with poor weatherstripping leak significantly. ~15 CFM50 per typical hatch isn’t unusual.

Bath fan ducts that terminate in the attic. Code requires they terminate outside. Some installations terminate in the soffit, which essentially terminates in the attic. Each one is a 30+ CFM50 leak.

For a detailed walkthrough of all the failure patterns and how to fix each one, see our article on why Ocala homes fail blower door tests.

How the Test Connects to Your Manual J

The Manual J load calculation uses an assumed infiltration rate. For Florida new construction, that assumption is typically derived from a 5.0 ACH50 target.

If your blower door test comes back at 7.0 ACH50, the actual infiltration is higher than the Manual J assumed. This means:

• Cooling load is higher than calculated
• Heating load is higher than calculated
• The selected HVAC equipment may now be undersized for the actual envelope performance

The fix is to seal the envelope to hit the 5.0 ACH50 target, which the Manual J was based on. Re-engineering the equipment is rare — it’s much cheaper to find and fix the leaks.

What Marion County Reviewers Check

When a blower door test report is submitted with the certificate of occupancy package, Marion County reviewers check:

• Test was performed by qualified technician. The signature on the report should be from someone certified to perform blower door testing.
• Test was performed per ANSI/RESNET/ICC 380. The standard methodology must be followed.
• Result is ≤5.0 ACH50 (or meets the project’s specific performance-path target).
• Result documentation includes date, address, square footage, conditioned volume, and CFM50.
• The infiltration value used in the Form R405-2023 matches the test result (or is conservative — i.e., the Form assumes worse, the test was better).

How B&I Testing Handles Blower Door Tests for Marion County

B&I Testing performs blower door tests throughout Marion County using calibrated Energy Conservatory equipment (the industry standard) and ANSI/RESNET/ICC 380 methodology. We provide the certified test report builders need for certificate of occupancy approval.

If your home fails the initial test, we can perform a leak-finding pass on the same visit to help identify where to seal — saving you a second trip and a second test fee.

If you need a blower door test for an Ocala or Marion County project, call (352) 756-2986, email brandon@banditesting.com, or reach us through the contact form.

Frequently Asked Questions

What’s the maximum ACH50 for Marion County new construction? 5.0 ACH50 is the absolute ceiling under any compliance path per FBC-EC R402.4.1.2. The prescriptive testing limit for Climate Zones 1 and 2 is 7 ACH50, but the 5.0 ceiling overrides it. Below 3 ACH50, the building department verifies that whole-house mechanical ventilation has been installed.

When is the test performed? After drywall, before final inspection. Usually at the trim-out / paint-ready stage.

What if my house fails the test? We perform a leak-finding pass to identify the major air leakage locations. After your team seals those areas, we re-test. Many homes pass on the second test once obvious penetrations are sealed.

How long does a blower door test take? About 30–60 minutes once the house is prepared. House preparation (closing windows, turning off fans, sealing required vents per protocol) takes another 15 minutes.

Do I need a blower door test for a renovation or addition? Substantial additions (typically >50% of original conditioned area) require testing. Smaller renovations may not, depending on scope. Call (352) 756-2986 to discuss your specific project.