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  • STUDY GUIDES
    • HERS RATER WRITTEN EXAM >
      • Section 1 Building Science Fundamentals >
        • 1a. Basic Terms & Definitions >
          • 1. Airflow in Buildings
          • 2. Equipment Efficiencies
          • 3. Power and Energy
          • 4. Effective Leakage Area
          • 5. Area Weighted R-Value
          • 6. Baseload / Seasonal Energy Use
          • 7. Driving Forces (Including Natural and Mechanical)
          • 8. Behavior of Radiation
          • 9. Thermal Resistance / Transmittance: R and U Values
          • 10. Latent / Sensible Heat
          • 11. Total Equivalent Length
          • 12. Dehumidification / Humidification
          • 13. Convert Pressure Units
          • 14. Thermal Bridges
          • 15. Pressure Boundary
          • 16. Stack Effect
          • 17. Exfiltration and Infiltration
          • 18. Natural / Mechanical Ventilation
          • 19. Net Free Area
          • 20. Input & Output Capacity
          • 21. Peak Electrical Demand
          • 22. Permeability and Perm Rating
          • 23. Standby Loss
          • 24. IAQ (indoor air quality): Moisture, CO, Dust
        • 1b. Principals of Energy, Air & Moisture Thermodynamics >
          • 1. Thermodynamics: Conduction, Convection, Radiation, ΔT
          • 2. Factors That Affect Insulation Performance
          • 3. House Pressurization/Depressurization by Various Forces
          • 4. Heat Gain / Loss
          • 5. Power and Energy
          • 6. Moisture Transport Mechanisms
          • 7. Identify Areas of Highest Relative Humidity
          • 8. Principles of Combustion
        • 1c. Combustion Safety >
          • 1. Combustion Analysis
          • 2. Carbon Monoxide (CO) Testing
          • 3. Combustion Appliance Venting, Draft, Combustion Air & Sizing
          • 4. Understand Combustion Safety Issues
      • Section 2 Buildings and Their Systems >
        • 2a. Building Components >
          • 1. Identify basic duct configurations and components
          • 2. Identify Basic Hydronic Distribution Configurations and Components
          • 3. Identify Basic Structural Components of Residential Construction
          • 4. Thermal Boundaries and Insulation Applications
          • 5. Basic Electrical Components and Safety Considerations
          • 6. Basic Fuel Delivery Systems and Safety Considerations
          • 7. Basic bulk water management components (drainage plumbing gutters sumps etc)
          • 8. Vapor barriers/retarders
          • 9. Radiant Barrier Principles and Installations
          • 10. Understand Fenestration Types and Efficiencies
          • 11. Understand Issues Involved With Basements, Crawlspaces, Slabs, Attics, Attached Garages, Interstitial Cavities, and Bypasses
          • 12. Understand Issues Involved With Ventilation Equipment
          • Understand Basic Heating / Cooling Equipment Components Controls and Operation
          • Understand Basic DHW Equipment Components Controls and Operation
          • Identify Common Mechanical Safety Controls
          • Identify Insulation Types and R-Values
          • Understand Various Mechanical Ventilation Equipment and Strategies: Spot, ERV, HRV
        • Conservation Strategies >
          • Appropriate Insulation Applications and Installation Based On Existing Conditions
          • Opportunity for ENERGY STAR Lighting and Appliances
          • Identify Duct Sealing Opportunities and Applications
          • Understand Importance of Air Leakage Control and Remediation Procedures
          • Blower Door-Guided Air Sealing Techniques
          • Water Conservation Devices and Strategies
          • Domestic Hot Water (DHW) Conservation Strategies
          • Heating & Cooling Efficiency Applications
          • Proper Use of Modeling to Determine Heating and Cooling Equipment Sizing and Appropriate Energy
          • Understand the Use of Utility History Analysis in Conservation Strategies
          • Appropriate Applications For Sealed Crawlspaces Basements and Attics
          • Identify / Understand High Density Cellulose
          • Appropriate Applications for Fenestration Upgrades Including Modification or Replacement
        • Comprehensive Building Assessment Process >
          • Determine Areas of Customer Complaints / Concerns in Interview
          • Understand / Recognize Need For Conducting Appropriate Diagnostic Procedures
          • Interaction Between Mechanical Systems, Envelope Systems and Occupant Behavior
        • Design Considerations >
          • Appropriate Insulation Applications Based On Existing Conditions
          • Understand Fire Codes as Necessary to Apply Home Performance in a Code-Approved Manner
          • Understand / Recognize Building Locations Where Opportunities for Retrofit Materials
          • Understand Climate Specific Concerns
          • Understand Indoor Environment Considerations for the Environmentally Sensitive
          • Understand Impact of Building Orientation, Landscape Drainage, and Grading
          • Opportunity Potential Renewable Energy Applications: Geothermal, Photovoltaic, Wind
          • Understand Impact of Shading on Heating / Cooling Loads
          • Awareness for Solar Gain Reduction / Solar Gain Opportunities
          • Understand Need for Modeling Various Options For Efficiency Upgrades
      • Measurement & Verification of Building Performance >
        • Measurement & Verification of Building Performance >
          • Air Leakage Test Results
          • Understand Building Shell / Envelope Leakage
          • Apply Fundamental Construction Mathematics and Unit Conversions
          • Calculate Building Tightness Levels (Minimum Ventilation Requirements)
          • Calculate Heating Degree Days and Cooling Degree Days
          • Identify Proper Appliance and Combustion Appliance Venting
          • Ventilation calculations and strategies
          • Proper methods for identifying / testing fuel leaks
          • Blower door setup, accurate measurement and interpretation of results
          • Combustion Appliance Zone (CAZ): depressurization, spillage, draft, Carbon Monoxide (ambient and flue)
          • Carbon Monoxide (CO) evaluation: ambient
          • Proper applications and use of temperature measuring devices
          • Pressure pan and room to room pressure diagnostics
          • Recognize contributing factors to comfort problems
          • Inspect for areas containing moisture or bulk water in undesirable locations
          • Understand and inspect for basic electric safety (e.g. frayed wires, open boxes, etc)
      • RESNET HERS RATER National Standards & Project Specifications >
        • Understand applicability content and intent of BPI National Standards – Do no harm, make buildings more healthy, comfortable, durable and energy efficient
        • Recognize need for a professional local/state/national codes evaluation
        • Be able to specify appropriate materials and processes needed for building performance projects
      • Analyzing Buildings Systems >
        • Recognize need for air sealing measures and their impact on other building systems
      • Conduct and Communications >
        • Conservation strategies
        • Conservation strategies
    • HERS RATER FIELD EXAM >
      • How To Put The House Under Worst Case & CAZ
      • What's What? Pa, CFM, CFM50, CAZ, Draft, Room Pressure
      • What To Know In The Attic
      • What To Know In The House
    • BLOWER DOOR TEST >
      • Manometer Setup
    • RESNET STANDARDS >
      • RESNET Standards Decoded
  • ESSENTIALS
    • HELP, I HATE MATH!
    • AUDITOR TO CREW COMMUNICATION
    • COMMON AUDITOR / CREW MISTAKES
    • RUN LIKE HELL
    • CONTACT
  • AFTER THE EXAM
    • GROW YOUR HOME PERFORMANCE BUSINESS
    • START A HOME PERFORMANCE BUSINESS
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Combustion Appliance Zone (CAZ): Depressurization, Spillage, Draft, Carbon Monoxide (Ambient and Flue)

CAZ

We need to test and check if conditions in the home can create backdrafting, spillage or flame rollout. CAZ pressures may overcome the draft pressure needed to safely exhaust hot water tanks and furnaces. To create worst case conditions, we should turn on every device that can create a negative pressure in the house and then measure the negative pressure created where the combustion appliance is located and compare that pressure to the outside (aka WRT outside).

Draft

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Draft test tells us the pressure difference between the two ends of the flue

Input A: With the water heater / atmospheric furnace turned on, measure the flue draft with the hose connected to the draft probe and record draft after appliance is fired up within the first minute of operation.  

Drill your hole between 12-inches and 24-inches from the top of the diverter on naturally vented appliances

BPI standards


  • < 10 degree F outside requires -2.5 Pa or more negative
  • 10 – 90 degrees F outside requires formula (T/40) – 2.75 Pa or more negative
  • > 90 degrees F requires -0.5 Pa or more negative
View a video of the process at the link below https://youtu.be/pt5cLet2fj8.

Depressurization

Depressurization does not just happen to a home when you run your blower door, it happens under natural conditions as well.  Think about when you have your exhaust vans running, kitchen range hood, dryer and central vacuum system… those are all mini blower doors running on depressurization.  What about natural draft chimneys and the stack effect of warm air rising and sucking in cooler air from the house… that’s depressurization.  Or finally on a windy day when one side of a house is getting hit with wind, what is happening to the other side of the house?  It’s sucking the air from the house which is the same as depressurization.  And the danger of depressurization is back drafting of CO into the home, so it’s something we want to avoid and is why we put the home under worst case conditions with all the fans on and doors closed.  We are trying to make the house fail and spill CO into the home while we are there, under controlled conditions so we can recommend and fix the problem.  

Spillage

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Spillage occurs when combustion gases spill out of a gas appliances’ flue and into the home.  This could happen because of depressurization as mentioned above, or because something is blocking the flue pipe.  Sometimes bird like to keep warm on the flue and block one side of it, or it could be clogged with twigs from their nest.  We can test spillage with a smoke pen, going 360 degrees around open diverters of water heaters and furnaces.  If at any point, the smoke from the pen or incense stick does not go up the flue, the appliance has failed the spillage test and further remediation needs to be taken.

Carbon Monoxide (CO): Ambient

One of the quickest ways to fail the BPI field exam is to forget to turn on your ambient CO meter before you walk in the house.  A CO monitor like the one shown below should be on from the moment you leave your car to walk across the front sidewalk.   The ambient CO meter tells you the presence of the deadly gas carbon monoxide (not the same as carbon dioxide, which is harmless) by a series of beeps.  The more frequent the beeps, the more CO is in the air and per BPI Standard if the ambient CO level ever gets above 35 ppm, you need to evacuate the home immediately and open the windows to ventilate the home.  You must stop your evaluation until the problem has been fixed, then and only then can you continue retesting the home.  



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Carbon Monoxide (CO): Flue

Carbon monoxide is formed from the incomplete combustion of carbon dioxide.  CO is deadly and needs to be measured in all gas appliances.  Combustion appliances with power vents like an 80% AFUE furnace can have the CO measured at the outlet terminal (outside).  Combustion appliances with open draft diverters (you can stick your fingers in the diverter) should have an undiluted CO measurement taken.  In ovens, this is in the throat of the flue as shown below.

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Next Section

3a. Applied diagnostics and troubleshooting
  1. Application of measured air leakage test results 
  2. Understand building shell/envelope leakage as a function of pressure difference and the size of holes in the air barrier 
  3. Apply fundamental construction mathematics and unit conversions 
  4. Calculate building tightness levels (minimum ventilation requirements) 
  5. Calculate heating degree days and cooling degree days 
  6. Identify proper appliance and combustion appliance venting 
  7. Ventilation calculations and strategies 
  8. Proper methods for identifying / testing fuel leaks 
  9. Blower door setup, accurate measurement and interpretation of results 
  10. Combustion Appliance Zone (CAZ): depressurization, spillage, draft, Carbon Monoxide (ambient and flue) 
  11. Carbon Monoxide (CO) evaluation: ambient 
  12. Proper applications and use of temperature measuring devices 
  13. Pressure pan and room to room pressure diagnostics 
  14. Recognize contributing factors to comfort problems 
  15. Inspect for areas containing moisture or bulk water in undesirable locations 
  16. Understand and inspect for basic electric safety (e.g. frayed wires, open boxes, etc) 
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