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CFM50 Calculation:
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CFM50 (Cubic Feet per Minute at 50 Pascals) is a standard measurement of air leakage rate in building envelope testing. It quantifies the amount of air flowing through a building's envelope at a pressure difference of 50 Pascals.
The calculator uses the CFM50 conversion formula:
Where:
Explanation: The formula converts airflow measurements at various pressure differences to the standardized 50 Pa reference pressure using the square root relationship between airflow and pressure.
Details: CFM50 measurement is essential for evaluating building airtightness, energy efficiency, and indoor air quality. It helps identify air leakage paths and quantify infiltration rates for energy modeling and ventilation system design.
Tips: Enter the measured flow rate in CFM and the corresponding pressure measurement in Pascals. Both values must be positive numbers measured during a blower door test.
Q1: Why use 50 Pascals as the reference pressure?
A: 50 Pa is a standard reference pressure that provides a measurable pressure difference while maintaining test safety and equipment limitations.
Q2: What is a good CFM50 value for a typical home?
A: Values vary by climate and house size, but generally, lower CFM50 values indicate tighter construction. New energy-efficient homes typically range from 500-1500 CFM50.
Q3: How does CFM50 relate to ACH50?
A: ACH50 (Air Changes per Hour at 50 Pa) is calculated by dividing CFM50 by the building volume and converting to hourly rate. ACH50 = (CFM50 × 60) / Volume.
Q4: When should blower door testing be performed?
A: Ideal times include during construction before drywall installation, after completion to verify airtightness, and during energy audits to identify air leakage issues.
Q5: Are there limitations to CFM50 measurements?
A: CFM50 represents artificial conditions and doesn't directly equate to natural infiltration rates, but it provides a valuable comparative metric for building performance.