Blower Door Testing in Eastern Iowa

What a Blower Door Test Measures

A blower door is a calibrated fan that temporarily replaces one of your exterior doors. We seal the fan into the opening, turn it on, and pull air out of the house until the inside is at a 50-Pascal pressure difference from the outside. At that point, every gap, crack, and unsealed penetration in the building envelope is trying to pull outside air in. The fan measures how much air has to move to hold that pressure difference — and that number tells us how leaky the house is.

Two numbers come out of the test:

• CFM50 — Cubic Feet per Minute at 50 Pascals. The raw airflow through the fan: a direct measure of how much air the house is leaking.
• ACH50 — Air Changes per Hour at 50 Pascals. CFM50 normalized to the size of your house. It tells you how many times the entire volume of air inside the home would be replaced in one hour at test pressure. ACH50 is the number most codes, programs, and energy raters use.

CFM50 is how much air is moving. ACH50 is how fast the house loses its air relative to its size. A small tight house and a large loose house can share a CFM50 and have very different ACH50 numbers — which is why we report both.

When You Need a Blower Door Test

There are four common reasons homeowners and builders in Eastern Iowa call us for a blower door test:

1. New Construction Code Compliance

The Iowa energy code requires a blower door test on every new home, with a maximum leakage of 4.0 ACH50. For a builder, the test is a final check before the certificate of occupancy. For a homeowner having a house built, it is independent verification that the envelope was actually built tight, not just drawn tight.

2. Pre-Purchase Inspection

A standard home inspection will tell you the furnace is 12 years old. It will not tell you the house leaks like a sieve. A blower door test before closing gives you a real number for what you are buying and, more importantly, a preview of what the winter gas bill will look like. For older homes around Cedar Rapids and Iowa City, this is often the most useful pre-purchase test a buyer can order.

3. Post-Retrofit Verification

If you just had air sealing, insulation, or a major renovation done, the only way to know it worked is to measure. A before-and-after blower door test quantifies the improvement as a number. This is also required for most utility rebate programs and for any project that needs an updated HERS rating.

4. Diagnosing Comfort Problems

Cold bedroom over the garage. Drafty floors. A furnace that runs constantly. These are almost always envelope and air leakage problems, and a blower door is the single best tool for finding where the house is leaking. Combined with infrared imaging during the test, we can point directly at the top band joists, recessed lights, attic hatches, and duct chases, driving the problem.

What Happens During the Test

A standalone blower door test typically takes about two hours. Here is what the appointment looks like:

1. Setup and walkthrough (20–30 minutes). We review the house with you, identify the conditioned volume (basements and conditioned crawlspaces count as inside the envelope), close all exterior windows and doors, open all interior doors, and check combustion appliances. Exhaust fans, dryers, and HVAC systems get turned off or covered so they do not influence the test.
2. Fan installation (10 minutes). The blower door assembly goes into an exterior door opening — usually the front door. An adjustable frame seals the opening, and the calibrated fan mounts into the panel.
3. The test (10 minutes). We depressurize the house to 50 Pascals and record the airflow, typically taking multiple readings and sometimes running the fan at lower pressures to generate a full leakage curve.
4. Leak identification (30–45 minutes). While the house is under pressure, leaks are easy to find. We walk through with a smoke pencil, a thermal camera, or the back of a hand to identify the biggest leakage points. This is the part of the test that actually tells you what to do next.
5. Breakdown and report (15 minutes). The fan comes out, the house goes back to normal, and we review results with you on the spot. A written report follows.

What the Results Mean

Once we have your ACH50 number, here is roughly how to read it in an Iowa climate:

• Below 3.0 ACH50 — Tight. ENERGY STAR territory and the target for high-performance new construction. Mechanical ventilation is required at this tightness to maintain indoor air quality.
• 3.0 to 4.0 ACH50 — Code-compliant new construction. The 4.0 ACH50 target is the current Iowa new-construction ceiling.
• 4.0 to 7.0 ACH50 — Typical of well-built homes from the last 20 years or older homes that have been air sealed.
• 7.0 to 10.0 ACH50 — Typical of an average existing home in Eastern Iowa. Usually, a strong candidate for air sealing.
• Above 10.0 ACH50 — Leaky. Often, an older home with no air sealing work done, and a house that will see the biggest improvement from a weatherization project.

The number alone is not the point. What matters is the combination of the number and the walkthrough — knowing where the leaks are is what lets you prioritize the work that will actually move the number.

Cost

If your blower door test is part of a larger service — a DOE Home Energy Score, a RESNET HERS rating, or a BPI energy audit — the blower door is almost always included in the price of that service rather than billed separately.

Calibration and Credentials

Blower door numbers are only as good as the equipment and the protocol. We run calibrated Retrotec systems — the industry-standard manufacturer — and maintain them on the manufacturer’s recalibration schedule.

Testing follows BPI (Building Performance Institute) protocols. Home Star Iowa is a BPI Testing Center, and the owner, Rob Novak, has been a BPI Certified Building Analyst and BPI Certified Trainer since 2009. We are also a RESNET HERS Rater and a DOE Home Energy Score Assessor — a combination of credentials that is unusual in the Eastern Iowa market and means your test results are accepted by code officials, utility rebate programs, real estate professionals, and the ENERGY STAR program.

Service Area

We provide blower door testing throughout Eastern Iowa, including Cedar Rapids, Marion, Hiawatha, Iowa City, Coralville, North Liberty, Waterloo, and Cedar Falls, along with the smaller communities in between. If you are not sure whether your address is in range, call or email and ask — we are usually able to accommodate.

Frequently Asked Questions

Schedule a Blower Door Test

Ready to get a number on your house — or verify a new build meets code? Contact Home Star Iowa to schedule a blower door test anywhere in Eastern Iowa. If you are not sure whether a standalone test or a full energy audit is the right fit, call and ask. We will walk you through the options.

Every assessment is performed by Rob Novak, BPI-certified since 2009 →