Blower Door Inspection Calculator

ACH50 Equation:

\[ ACH50 = \frac{CFM50 \times 60}{Volume} \]

Air Changes Per Hour (ACH50):

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1. What is the ACH50 Equation?

The ACH50 (Air Changes per Hour at 50 Pascals) equation calculates the number of times the air in a building is completely replaced per hour when the building is pressurized to 50 Pa. It's a key metric in blower door tests for measuring building airtightness.

2. How Does the Calculator Work?

The calculator uses the ACH50 equation:

\[ ACH50 = \frac{CFM50 \times 60}{Volume} \]

Where:

\( CFM50 \) — Airflow in cubic feet per minute at 50 Pa pressure difference
\( Volume \) — Interior volume of the building in cubic feet
\( 60 \) — Conversion factor from minutes to hours

Explanation: The equation converts the measured airflow at 50 Pa to air changes per hour based on the building's volume.

3. Importance of ACH50 Calculation

Details: ACH50 is a critical measurement for evaluating building envelope performance, identifying air leakage, and ensuring energy efficiency and indoor air quality in residential and commercial structures.

4. Using the Calculator

Tips: Enter CFM50 value from your blower door test and the building's interior volume. Both values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a good ACH50 value?
A: For energy-efficient homes, values below 3 ACH50 are excellent, while values above 7 ACH50 indicate significant air leakage needing attention.

Q2: How does ACH50 relate to natural infiltration?
A: ACH50 is measured under pressurized conditions and is typically 10-20 times higher than natural air changes under normal weather conditions.

Q3: When should blower door testing be performed?
A: Ideal during construction for quality control, after completion for verification, and during energy audits to identify improvement opportunities.

Q4: Are there limitations to ACH50 measurement?
A: Results can be affected by weather conditions, building occupancy, and testing procedures. Always follow standardized testing protocols.

Q5: How can ACH50 results be used?
A: Results help prioritize air sealing efforts, estimate energy losses from infiltration, and verify compliance with building energy codes.