HRAI Residential Mechanical Ventilation Design (HRAI RMV) Overview
These study notes are designed to prepare candidates for the HRAI Residential Mechanical Ventilation Design exam. They cover building science, IAQ fundamentals, CSA F326 standard, ventilation system selection, air distribution, controls, and commissioning. All content is anchored to official sources including HRAI, CSA, ASHRAE, and ACCA. Candidates should verify specific pass marks, eligibility, and regulatory details with HRAI.
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 IAQ Fundamentals
- CSA F326 Standard and Ventilation Requirements
- Ventilation System Selection and Configuration
- Air Distribution and Duct Design
- Controls and Electrical Integration
- Commissioning, Balancing, and Verification
Exam Snapshot and Readiness Target
Format: 80 questions, 120 minutes, pass mark 70% (practice baseline; verify with HRAI)
Candidate level: Technician/Designer - residential ventilation design
Readiness target: Demonstrate competence in designing mechanical ventilation systems per CSA F326 and good engineering practice
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 IAQ Fundamentals
Syllabus Focus
- Heat and moisture transfer in buildings
- Air leakage and pressure relationships
- Indoor air quality parameters (CO2, humidity, VOCs, particulates)
- Ventilation rates and dilution principles
- Stack effect, wind effect, and mechanical pressure imbalances
Key Notes
- Building envelope airtightness affects ventilation effectiveness; tighter homes require mechanical ventilation to meet IAQ targets.
- Moisture control is critical: relative humidity should be maintained between 30-60% to prevent mold and comfort issues.
- CO2 concentration is a proxy for occupancy ventilation; ASHRAE 62.2 recommends ≤700 ppm above outdoor levels.
- Stack effect drives air movement in cold climates; mechanical ventilation must account for natural driving forces.
- Ventilation dilutes indoor pollutants; source control (e.g., exhaust for kitchens/bathrooms) is the first line of defense.
Must Know
- Understand psychrometric chart: dew point, humidity ratio, enthalpy.
- Know typical IAQ contaminants: formaldehyde, radon, combustion byproducts, mold spores.
- Calculate ventilation rates based on floor area and number of bedrooms per CSA F326.
- Recognize the impact of negative pressure on backdrafting of combustion appliances.
Field and Exam Application
- Field: Measure building airtightness using blower door test to determine required ventilation rate.
- Design: Select HRV/ERV based on climate to manage humidity while providing fresh air.
- Troubleshooting: High indoor humidity in winter indicates inadequate ventilation or excessive moisture generation.
High-Yield Distinctions
- Difference between natural ventilation, infiltration, and mechanical ventilation.
- ASHRAE 62.2 vs CSA F326: both set ventilation rates but differ in calculation methods and applicability (US vs Canada).
- Supply-only vs exhaust-only vs balanced ventilation systems and their pressure effects.
Common Pitfalls
- Assuming infiltration credits can fully meet ventilation requirements in tight homes.
- Ignoring local exhaust requirements (kitchen/bathroom) when sizing whole-house ventilation.
- Confusing ventilation rate per person vs per floor area; CSA F326 uses floor area and bedrooms.
Review Tasks
- Practice calculating required ventilation rate for a 2000 sq ft home with 3 bedrooms using CSA F326.
- Sketch a psychrometric chart and identify the effect of adding moisture or heat.
- List three common indoor pollutants and their sources.
CSA F326 Standard and Ventilation Requirements
Syllabus Focus
- Scope and application of CSA F326
- Ventilation rate calculation methods
- Local exhaust requirements (kitchen, bathroom, laundry)
- Make-up air requirements for combustion appliances
- Compliance documentation and labeling
Key Notes
- CSA F326 applies to dwelling units with a floor area ≤ 500 m² (5382 ft²) and requires continuous mechanical ventilation.
- Total required ventilation rate = (floor area × 0.01 L/s per m²) + (number of bedrooms + 1) × 5 L/s.
- Local exhaust: kitchen ≥ 50 L/s intermittent or 20 L/s continuous; bathroom ≥ 25 L/s intermittent or 10 L/s continuous.
- Make-up air must be provided for exhaust appliances (e.g., range hood > 300 L/s) to prevent negative pressure.
- Systems must have a label indicating design airflow and date of installation.
Must Know
- Memorize the ventilation rate formula and apply it to various home sizes.
- Know the difference between intermittent and continuous exhaust rates.
- Understand that CSA F326 requires a ventilation system that operates at least 60% of each hour (or continuous).
- Recognize when make-up air is required: for exhaust systems > 300 L/s or for combustion safety.
Field and Exam Application
- Design: For a 250 m² home with 4 bedrooms, calculate required ventilation: (250×0.01) + (5×5) = 2.5 + 25 = 27.5 L/s.
- Inspection: Verify that the installed system label matches design airflow and that local exhaust meets minimums.
- Retrofit: When adding a high-CFM range hood, ensure make-up air is provided to avoid backdrafting.
High-Yield Distinctions
- CSA F326 vs ASHRAE 62.2: F326 uses floor area + bedrooms; 62.2 uses floor area + bedrooms but different constants.
- Intermittent vs continuous: intermittent requires higher flow but can cycle; continuous is lower flow but always on.
- Make-up air vs ventilation air: make-up air replaces exhausted air; ventilation air provides fresh air for occupants.
Common Pitfalls
- Forgetting to include the +1 bedroom in the formula (e.g., 3 bedrooms → 4 × 5 L/s).
- Using total floor area including basement if unfinished; F326 applies to conditioned space only.
- Assuming a single exhaust fan meets both local and whole-house ventilation without proper design.
Review Tasks
- Calculate ventilation rate for a 150 m² home with 2 bedrooms.
- List the minimum exhaust rates for a bathroom (intermittent and continuous).
- Describe when make-up air is required per CSA F326.
Ventilation System Selection and Configuration
Syllabus Focus
- Types of ventilation systems: exhaust-only, supply-only, balanced, HRV/ERV
- System selection criteria based on climate, home airtightness, and budget
- HRV/ERV core types and efficiency ratings
- Ducted vs ductless systems
- Integration with existing HVAC systems
Key Notes
- Exhaust-only systems are simple and low-cost but can cause negative pressure and backdrafting; not recommended for tight homes.
- Supply-only systems pressurize the home, reducing infiltration but may introduce unconditioned air.
- Balanced systems (HRV/ERV) provide equal supply and exhaust, maintaining neutral pressure and recovering energy.
- HRV transfers sensible heat; ERV transfers both sensible and latent heat, beneficial in humid climates.
- System selection must consider local climate: HRV preferred in cold climates, ERV in hot-humid to avoid moisture overload.
Must Know
- Advantages and disadvantages of each system type.
- How to size an HRV/ERV based on required ventilation rate and manufacturer specifications.
- Understand sensible and latent recovery efficiency and how they affect energy savings.
- Know that HRV/ERV must be installed with proper drainage for defrost cycles in cold climates.
Field and Exam Application
- Design: For a tight home in Winnipeg (cold climate), select an HRV with ≥60% sensible recovery efficiency.
- Troubleshooting: If an ERV in a humid climate is not controlling indoor humidity, check latent recovery performance.
- Retrofit: When adding ventilation to an existing forced-air system, use a balanced HRV to avoid pressure imbalances.
High-Yield Distinctions
- HRV vs ERV: HRV only transfers heat; ERV transfers heat and moisture. ERV can help maintain indoor humidity in dry climates.
- Ducted vs ductless: ducted systems distribute air to multiple rooms; ductless are simpler but may not meet all room requirements.
- Central fan integrated vs standalone: central fan integration uses the furnace fan to distribute ventilation air; standalone HRV has its own ductwork.
Common Pitfalls
- Selecting an ERV for a cold climate where frost management is critical; HRV is often better.
- Undersizing the HRV/ERV to save cost, leading to inadequate ventilation.
- Installing an exhaust-only system in a tight home without make-up air, causing negative pressure and backdrafting.
Review Tasks
- Compare HRV and ERV for a home in Miami vs Edmonton.
- List three criteria for selecting a ventilation system type.
- Calculate the required HRV airflow for a home needing 50 L/s ventilation.
Air Distribution and Duct Design
Syllabus Focus
- Duct sizing methods (equal friction, velocity reduction)
- Duct materials and leakage classes
- Supply and return grille placement
- Pressure drop calculations and fan selection
- Duct insulation and vapor barriers
Key Notes
- Duct design should follow ACCA Manual D or equivalent; use friction rate of 0.1 in.wg per 100 ft (0.8 Pa/m) as a starting point.
- Flexible duct should be installed straight and taut; excessive length and bends increase pressure drop.
- Supply registers should be located to provide good air mixing; avoid short-circuiting to return grilles.
- Return air pathways must be provided in each room with doors; transfer grilles or jump ducts are common solutions.
- Duct leakage can significantly reduce ventilation effectiveness; seal ducts to Class A or B per SMACNA.
Must Know
- How to use a duct sizing chart or calculator for round and rectangular ducts.
- Understand the impact of duct length, fittings, and flex duct on static pressure.
- Know the maximum recommended velocity for supply ducts (e.g., 800 fpm for main trunks).
- Recognize the need for balancing dampers to adjust airflow to each room.
Field and Exam Application
- Design: Size a 100 ft round duct to deliver 200 CFM at 0.1 in.wg/100 ft; use chart to find 8-inch diameter.
- Field: Measure static pressure across the HRV to verify it operates within manufacturer limits.
- Troubleshooting: Low airflow from a supply register may indicate undersized duct, excessive bends, or closed damper.
High-Yield Distinctions
- Equal friction vs velocity reduction: equal friction maintains constant friction loss per length; velocity reduction reduces velocity in larger ducts.
- Rigid vs flexible duct: rigid has lower pressure drop; flexible is easier to install but must be used carefully.
- Supply vs return: supply air should be delivered to occupied zones; return air should be from central locations or each room.
Common Pitfalls
- Using flex duct with sharp bends or kinks, causing high pressure drop.
- Oversizing ducts leading to low velocity and poor air mixing.
- Neglecting to include balancing dampers, making it impossible to adjust room airflows.
Review Tasks
- Size a duct run for 150 CFM using equal friction method.
- List three causes of high static pressure in a duct system.
- Explain why return air pathways are needed in bedrooms.
Controls and Electrical Integration
Syllabus Focus
- Ventilation system controls: timers, humidistats, CO2 sensors, occupancy sensors
- Interlocking with furnace/air handler
- Electrical requirements for HRV/ERV and fans
- Wiring diagrams and sequence of operation
- Code requirements for electrical connections (CEC)
Key Notes
- Ventilation systems should have a dedicated control to ensure continuous operation per CSA F326 (e.g., a timer or manual switch).
- HRV/ERV often interlock with the furnace fan to distribute fresh air; ensure proper wiring to avoid short cycling.
- Humidistat control can modulate ventilation based on indoor humidity; setpoint typically 50-60% RH.
- CO2 sensors can be used for demand-controlled ventilation (DCV) in high-occupancy spaces.
- All electrical work must comply with the Canadian Electrical Code (CEC); use licensed electricians for hardwiring.
Must Know
- Basic wiring of a low-voltage thermostat or control for HRV.
- Understand sequence of operation: HRV runs continuously or cycles with furnace fan.
- Know that ventilation systems require a dedicated circuit per CEC unless specified otherwise.
- Recognize the function of a defrost cycle in HRV and its control logic.
Field and Exam Application
- Installation: Wire an HRV to a furnace so that the HRV fan runs whenever the furnace fan runs (interlock).
- Troubleshooting: If HRV does not run, check control voltage (24V) and thermostat wiring.
- Commissioning: Set humidistat to 45% RH to avoid condensation on windows in winter.
High-Yield Distinctions
- Continuous vs intermittent control: continuous provides constant ventilation; intermittent cycles based on timer or sensor.
- Manual vs automatic: manual switches require occupant action; automatic controls (humidistat, CO2) adjust based on conditions.
- Low-voltage vs line-voltage controls: low-voltage (24V) for thermostats; line-voltage (120V) for direct fan control.
Common Pitfalls
- Wiring HRV to run only when furnace fan runs, but furnace fan cycles on thermostat demand, leading to inadequate ventilation.
- Using a standard light switch to control ventilation; CSA F326 requires a dedicated control that indicates system status.
- Forgetting to install a condensate drain for HRV defrost, causing water damage.
Review Tasks
- Draw a simple wiring diagram for an HRV interlocked with a furnace fan.
- List three types of automatic controls for ventilation.
- Explain the purpose of a defrost cycle in an HRV.
Commissioning, Balancing, and Verification
Syllabus Focus
- Airflow measurement techniques (flow hood, pitot tube, anemometer)
- Balancing dampers and procedures
- Verification of ventilation rates per CSA F326
- Documentation and labeling requirements
- Troubleshooting common issues (low airflow, noise, frost)
Key Notes
- Commissioning must verify that installed airflow meets design values within ±10% per CSA F326.
- Use a flow hood or calibrated anemometer to measure supply and exhaust flows at registers.
- Balancing dampers should be adjusted to achieve design airflow; start with all dampers open and measure each branch.
- Document all measurements on a commissioning report and affix a label near the system with design airflow and date.
- Common issues: low airflow due to undersized ducts, dirty filters, or blocked intakes; noise from high velocity or loose components.
Must Know
- How to use a flow hood correctly: ensure tight seal against register, measure in multiple locations if needed.
- Understand the procedure for balancing a multi-branch duct system.
- Know the acceptable tolerance for airflow measurement (±10% of design).
- Recognize signs of frost in HRV: reduced airflow, ice buildup on core; check defrost cycle and drainage.
Field and Exam Application
- Field: Measure total supply airflow at HRV unit using a pitot tube in the main duct; compare to design.
- Balancing: Adjust damper in bedroom branch to increase airflow from 30 CFM to 40 CFM as designed.
- Troubleshooting: If bathroom exhaust fan measures 20 CFM instead of 50 CFM, check for blocked duct or undersized fan.
High-Yield Distinctions
- Flow hood vs pitot tube: flow hood measures volume directly at register; pitot tube measures velocity in duct, requires area calculation.
- Static pressure vs velocity pressure: static pressure indicates resistance; velocity pressure indicates airflow speed.
- Commissioning vs verification: commissioning is the initial setup; verification is periodic testing to ensure continued performance.
Common Pitfalls
- Measuring airflow without ensuring all dampers are in their final position.
- Ignoring the impact of filter condition on airflow measurement.
- Failing to document measurements, making it impossible to verify compliance later.
Review Tasks
- Describe the steps to balance a ventilation system with three supply branches.
- List three tools used for airflow measurement.
- Explain what to do if measured airflow is 15% below design.
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 CSA F326 ventilation rate calculation and local exhaust requirements.
- Practice duct sizing using equal friction method and ACCA Manual D.
- Understand HRV/ERV selection criteria based on climate and home characteristics.
- Know commissioning procedures and airflow measurement techniques.
- Review control wiring and interlock sequences for HRV with furnace.
- Be able to troubleshoot common ventilation system issues (low airflow, noise, frost).
- Verify all information with official HRAI and CSA sources; pass mark and eligibility details are subject to change.
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.