BPI Infiltration and Duct Leakage (IDL) Overview
These study notes are designed to prepare candidates for the BPI Infiltration and Duct Leakage (IDL) certification exam. The notes cover building science fundamentals, blower door testing, duct leakage testing, zone pressure diagnostics, combustion safety, mechanical ventilation, and air sealing/duct repair strategies. All content is grounded in official sources including ASHRAE, ICC codes, ACCA manuals, and BPI standards. Candidates should verify specific pass marks, fees, and eligibility with BPI directly.
For Technical Conquer practice planning, this module is tracked as 80 questions over about 120 minutes with a listed pass mark of 70%. Treat those numbers as practice baselines and verify the current official format before scheduling.
How This Guide Is Organized
The sections below turn the syllabus into studyable subject blocks. Read a subject first, explain the must-know ideas without notes, then use questions, flashcards, and mind maps to test whether the knowledge holds under field-style pressure.
- Building Science and Airflow Fundamentals
- Blower Door Testing and Infiltration Analysis
- Duct Leakage Testing Methodologies
- Zone Pressure Diagnostics (ZPD)
- Combustion Safety and Mechanical Ventilation
- Air Sealing and Duct Repair Strategies
Exam Snapshot and Readiness Target
Format: 80 questions, 120 minutes, pass mark 70% (practice baseline; verify with BPI)
Candidate level: Entry-level to technician; suitable for energy auditors, weatherization technicians, and HVAC professionals
Readiness target: Demonstrate knowledge of building science, diagnostic testing, safety, and repair strategies for infiltration and duct leakage
Most candidates should budget at least 36+ focused study hours, then adjust upward for unfamiliar equipment, code, regulatory, commissioning, controls, or calculation-heavy content.
Building Science and Airflow Fundamentals
Syllabus Focus
- Stack effect
- Wind effect
- Mechanical ventilation
- Air barriers and thermal boundaries
- Pressure relationships
Key Notes
- Stack effect: warm air rises, creating positive pressure at top and negative at bottom; magnitude depends on building height and indoor-outdoor temperature difference.
- Wind effect: windward side positive pressure, leeward side negative; pressure differences drive infiltration.
- Mechanical ventilation: balanced, supply-only, or exhaust-only systems affect building pressure and infiltration.
- Air barriers must be continuous and aligned with thermal boundary to prevent condensation and energy loss.
- Building envelope leakage is quantified by ACH50 (air changes per hour at 50 Pa) or CFM50 (cubic feet per minute at 50 Pa).
- Neutral pressure plane (NPP) is the level where indoor pressure equals outdoor; moves with temperature and wind.
Must Know
- Define ACH50 and CFM50 and how they relate to building tightness.
- Explain stack effect and wind effect on infiltration.
- Identify the difference between air barrier and vapor retarder.
- Understand how mechanical systems affect building pressure.
Field and Exam Application
- Use blower door to measure building leakage and calculate ACH50.
- Diagnose comfort complaints due to stack effect in multi-story buildings.
- Evaluate ventilation needs based on building tightness.
High-Yield Distinctions
- ACH50 vs. natural ACH: natural ACH is typically ACH50 divided by 20 (rule of thumb).
- Air barrier vs. thermal barrier: air barrier stops airflow; thermal barrier stops heat flow.
- Stack effect vs. wind effect: stack effect is temperature-driven; wind effect is pressure-driven.
Common Pitfalls
- Confusing ACH50 with natural infiltration rate.
- Assuming air barrier and vapor retarder are the same.
- Ignoring mechanical system impacts on building pressure.
Review Tasks
- Calculate ACH50 from CFM50 and building volume.
- Sketch pressure zones in a two-story house during winter.
- List three factors that affect neutral pressure plane.
Blower Door Testing and Infiltration Analysis
Syllabus Focus
- Blower door components and setup
- Test procedures (pressurization/depressurization)
- Multi-point vs. single-point tests
- Data interpretation
- Limitations and corrections
Key Notes
- Blower door consists of a calibrated fan, pressure gauge, and mounting frame; measures airflow at a given pressure difference.
- Standard test pressure is 50 Pa (0.2 in w.c.) for building leakage; results reported as CFM50 or ACH50.
- Depressurization is preferred to avoid opening doors/windows; pressurization may be used for verification.
- Multi-point test measures leakage at several pressures to calculate C and n coefficients (flow exponent).
- Single-point test assumes n=0.65; less accurate but faster.
- Corrections: temperature, altitude, and wind affect readings; use manufacturer corrections.
Must Know
- Steps to set up and operate a blower door.
- How to calculate ACH50 from CFM50 and building volume.
- Difference between single-point and multi-point tests.
- When to use pressurization vs. depressurization.
Field and Exam Application
- Conduct a blower door test to determine building tightness.
- Identify leakage sites using smoke pencil during test.
- Use results to prioritize air sealing measures.
High-Yield Distinctions
- CFM50 vs. CFM25: CFM50 is standard; CFM25 used for duct leakage.
- n exponent: 0.5 (turbulent) to 1.0 (laminar); typical building n=0.65.
- Effective leakage area (ELA) vs. CFM50: ELA is calculated from flow and pressure.
Common Pitfalls
- Testing with windows open or exhaust fans running.
- Ignoring wind speed limits (typically <5 mph).
- Using wrong building volume (include all conditioned space).
Review Tasks
- Calculate ACH50 for a 2000 ft² house with 8 ft ceilings and CFM50=1500.
- List three conditions that invalidate a blower door test.
- Explain why depressurization is preferred.
Duct Leakage Testing Methodologies
Syllabus Focus
- Duct leakage to outside vs. total leakage
- Duct blaster setup and operation
- Test procedures (pressurization/depressurization)
- Leakage classification
- Code requirements (IMC, IECC)
Key Notes
- Duct leakage is measured at 25 Pa (0.1 in w.c.) for residential; total leakage includes all leaks, leakage to outside only those to unconditioned space.
- Duct blaster is a calibrated fan connected to duct system; measures airflow at test pressure.
- Two methods: total leakage test (all registers sealed) and leakage to outside test (registers unsealed, house pressurized).
- IMC requires duct leakage to outside ≤ 4% of total airflow for new construction (or ≤ 8% if total leakage tested).
- IECC requires duct leakage to outside ≤ 4% for new systems; existing systems ≤ 10%.
- Leakage classification: A (tight), B (moderate), C (leaky) based on CFM25 per 100 ft² of floor area.
Must Know
- Difference between total leakage and leakage to outside.
- How to set up and operate a duct blaster.
- Code thresholds for duct leakage (IMC and IECC).
- How to calculate leakage percentage.
Field and Exam Application
- Test duct leakage to outside to verify code compliance.
- Identify leak locations using smoke or pressure pan.
- Prioritize duct sealing based on leakage severity.
High-Yield Distinctions
- Total leakage vs. leakage to outside: total includes leaks inside conditioned space; leakage to outside is energy-relevant.
- Duct blaster vs. blower door: duct blaster tests ducts; blower door tests building envelope.
- CFM25 vs. CFM50: duct leakage tested at 25 Pa; building leakage at 50 Pa.
Common Pitfalls
- Testing ducts with HVAC system running (should be off).
- Sealing all registers for total leakage test but forgetting to seal returns.
- Confusing leakage percentage with CFM25.
Review Tasks
- Calculate leakage percentage if duct blaster reads 200 CFM25 and system airflow is 1200 CFM.
- List steps for a leakage-to-outside test.
- Compare IMC and IECC duct leakage requirements.
Zone Pressure Diagnostics (ZPD)
Syllabus Focus
- Pressure measurements in rooms and zones
- Identifying pressure imbalances
- Diagnosing duct system problems
- Combustion appliance zone (CAZ) testing
- Pressure limits for safety
Key Notes
- ZPD measures pressure difference between rooms and reference (e.g., outdoors or main body) to identify imbalances.
- Common causes: closed doors, undersized returns, blocked ducts, or unbalanced supply.
- CAZ testing: measure pressure in room containing combustion appliances; limit is -5 Pa relative to outdoors (or -3 Pa per BPI).
- Pressure imbalances can cause backdrafting of combustion appliances, comfort issues, and energy loss.
- Use digital manometer with range ±25 Pa; record pressures with all doors open and closed.
- Diagnostic steps: measure baseline, then operate HVAC, then operate exhaust fans.
Must Know
- How to measure zone pressure with a manometer.
- Maximum allowable negative pressure in CAZ.
- How to interpret pressure readings to diagnose duct issues.
- Steps for CAZ testing.
Field and Exam Application
- Diagnose a room that is too hot or cold using ZPD.
- Test CAZ pressure to ensure combustion safety.
- Identify undersized return ducts causing negative pressure.
High-Yield Distinctions
- ZPD vs. blower door: ZPD measures pressure differences; blower door measures leakage.
- CAZ limit: -5 Pa (some codes) vs. -3 Pa (BPI).
- Pressure with doors open vs. closed: closed doors often reveal imbalances.
Common Pitfalls
- Measuring pressure with HVAC off when system is the cause.
- Ignoring reference point (should be outdoors or neutral zone).
- Not checking for backdrafting after ZPD.
Review Tasks
- Measure pressure in a bedroom with door closed and HVAC running; interpret if reading is -2 Pa.
- List three causes of negative pressure in a CAZ.
- Explain why -5 Pa is a safety limit.
Combustion Safety and Mechanical Ventilation
Syllabus Focus
- Combustion appliance types (atmospheric, sealed, power-vented)
- Spillage and backdrafting
- Carbon monoxide (CO) testing
- Ventilation standards (ASHRAE 62.2)
- Interaction between tight buildings and ventilation
Key Notes
- Atmospheric combustion appliances rely on natural draft; can spill or backdraft if depressurized.
- Sealed combustion and power-vented appliances are safer in tight homes.
- CO testing: measure ambient CO and flue gas CO; action levels: 9 ppm ambient (EPA), 25 ppm flue (BPI).
- ASHRAE 62.2 requires mechanical ventilation for homes with infiltration rate below 0.35 ACH natural.
- Ventilation rate: CFM = 0.01 × floor area (ft²) + 7.5 × (bedrooms + 1).
- Tight buildings need controlled ventilation to maintain indoor air quality.
Must Know
- Difference between atmospheric and sealed combustion.
- CO action levels and testing procedure.
- ASHRAE 62.2 ventilation rate formula.
- How to test for spillage and backdrafting.
Field and Exam Application
- Test for backdrafting after air sealing.
- Calculate required ventilation for a 2000 ft² home with 3 bedrooms.
- Install CO alarms in homes with combustion appliances.
High-Yield Distinctions
- Spillage vs. backdrafting: spillage is temporary; backdrafting is continuous reversal of flue gases.
- Atmospheric vs. sealed combustion: sealed combustion draws air from outside.
- ASHRAE 62.2 vs. local codes: local codes may be more stringent.
Common Pitfalls
- Assuming all combustion appliances are safe in tight homes.
- Not testing CO after weatherization.
- Oversizing ventilation leading to energy waste.
Review Tasks
- Calculate ventilation CFM for a 1500 ft² home with 2 bedrooms.
- List steps for a spillage test on a water heater.
- Explain why CO testing is critical after air sealing.
Air Sealing and Duct Repair Strategies
Syllabus Focus
- Air sealing materials and methods
- Duct sealing materials (mastic, tape, aerosol)
- Prioritizing leaks
- Safety considerations
- Code compliance for repairs
Key Notes
- Air sealing: caulk, spray foam, weatherstripping, and rigid materials for large gaps.
- Duct sealing: mastic (preferred), UL-181 tape, or aerosol-based sealing; avoid standard duct tape.
- Prioritize leaks: attic-to-house leaks, rim joists, duct connections, and penetrations.
- Safety: avoid sealing around combustion appliance flues; maintain combustion air openings.
- Code: repairs must meet IMC and IECC requirements; duct sealing must be permanent.
- After sealing, retest to verify leakage reduction.
Must Know
- Appropriate materials for air sealing different gaps.
- Why mastic is preferred over duct tape.
- How to prioritize air sealing for maximum energy savings.
- Safety rules when sealing near combustion appliances.
Field and Exam Application
- Seal attic bypasses to reduce stack effect.
- Apply mastic to duct joints to reduce leakage.
- Use blower door to verify air sealing effectiveness.
High-Yield Distinctions
- Mastic vs. tape: mastic is more durable and code-compliant for ducts.
- Air sealing vs. insulation: air sealing stops airflow; insulation stops heat flow.
- Permanent vs. temporary repairs: code requires permanent sealing.
Common Pitfalls
- Using duct tape on ducts (fails quickly).
- Sealing combustion air openings.
- Not retesting after sealing to confirm improvement.
Review Tasks
- List three materials for air sealing and their best applications.
- Explain why mastic is preferred for duct sealing.
- Describe the steps to seal a duct joint properly.
How To Use These Notes With Practice Questions
Do not jump straight from reading to a full mock. Work by subject first: review the key notes, make a short recall sheet from memory, then answer a focused question set. After each miss, decide whether the problem was missing theory, weak code/source recall, poor measurement setup, calculation error, or a field sequence you did not visualize.
Technical Conquer's question bank, flashcards, mind maps, and spaced review tools are most useful after this instruction layer because they reveal which parts of the notes are not yet retrievable.
Final Review Checklist
- Review building science fundamentals: stack effect, wind effect, and pressure relationships.
- Practice blower door setup and calculation of ACH50.
- Understand duct leakage testing methods and code thresholds.
- Master zone pressure diagnostics and CAZ safety limits.
- Know combustion safety testing and ASHRAE 62.2 ventilation requirements.
- Familiarize with air sealing materials and duct repair best practices.
- Verify all code references with current IMC, IECC, and BPI standards.
- Take practice exams to assess readiness; aim for 80%+ before exam day.
Official Sources and Further Reading
Use these sources as the final authority for format, eligibility, rules, regulatory limits, and exam updates. Study notes are a preparation layer, not a replacement for official candidate guidance.