Infiltration Rate

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Infiltration Rate

What is Infiltration Rate?

The measurement of uncontrolled air leakage into a building through cracks, gaps, and other unintentional openings in the building envelope, typically expressed in air changes per hour or cubic feet per minute, critical for energy efficiency, indoor air quality, and building performance analysis.

Description

Infiltration rate is the measurement of uncontrolled air leakage into a building through cracks, gaps, and other unintentional openings in the building envelope, typically expressed in air changes per hour or cubic feet per minute, critical for energy efficiency, indoor air quality, and building performance analysis. This fundamental building science metric quantifies how much outside air enters a building without being filtered, conditioned, or controlled, directly impacting energy consumption, comfort, and indoor environmental quality. Understanding and controlling infiltration rates is essential for achieving high-performance building design and operation.

The primary significance includes direct impact on heating and cooling energy consumption, influence on indoor air quality and comfort, effect on building pressurization and ventilation effectiveness, contribution to moisture problems and condensation issues, impact on HVAC system sizing and performance, and importance for building code compliance and energy certifications.

Measurement units encompass air changes per hour (ACH) indicating complete air volume replacement frequency, cubic feet per minute (CFM) showing actual air volume flow, cubic feet per minute per square foot of building envelope area, and liters per second per square meter for international applications.

FAQs

  • What is infiltration rate?

    Infiltration rate measures uncontrolled air leakage into a building through cracks, gaps, and unintentional openings in the building envelope, typically expressed in air changes per hour or cubic feet per minute.

  • How is infiltration rate measured?

    It’s measured using blower door testing, tracer gas testing, infrared thermography, and pressure differential measurements, with blower door testing being the most common method.

  • What units are used for infiltration rate?

    Common units include air changes per hour (ACH), cubic feet per minute (CFM), CFM per square foot of envelope area, and liters per second per square meter.

  • What causes air infiltration in buildings?

    Common sources include gaps around windows and doors, electrical penetrations, plumbing openings, construction joints, attic connections, and HVAC system leaks.

  • Why is controlling infiltration rate important?

    It’s important for energy efficiency, indoor air quality, comfort, moisture control, HVAC system performance, and building code compliance.

  • What are typical infiltration rates for buildings?

    Rates vary widely: older homes may have 10–15 ACH50, newer homes 3–7 ACH50, and high-performance buildings under 1 ACH50 (measured at 50 Pascal pressure difference).

  • How can infiltration rates be reduced?

    Reduction methods include comprehensive air sealing, proper weather stripping, sealing penetrations, installing continuous air barriers, and regular maintenance of envelope components.

Fun Fact

Fun Fact: A typical older home can have air leakage equivalent to leaving a window open 24/7! The stack effect in tall buildings can create pressure differences equivalent to 30+ mph winds. Modern Passive House buildings achieve infiltration rates so low (0.6 ACH50) that they’re nearly airtight. Interestingly, reducing infiltration by just 1 ACH can save 10-20% on heating and cooling costs in most climates!

CSI Code

07 27 00

NAHB Code

725