HRV Sizing Calculator

EN 13053ASHRAE
Calculator Input
Enter space specifications and HRV parameters
m²

Total floor area of the space

Total number of people in the space

m

Height from floor to ceiling

%

Efficiency of the HRV unit

°C

Indoor - outdoor temperature difference

Frequently Asked Questions

Common questions about this calculator

A Heat Recovery Ventilator (HRV) exchanges stale indoor air with fresh outdoor air while recovering 70-90% of heat energy. A heat exchanger core transfers thermal energy between outgoing and incoming airstreams without mixing them. This provides ventilation without wasting heating/cooling energy.

HRV (Heat Recovery Ventilator) transfers only sensible heat (temperature). ERV (Energy Recovery Ventilator) transfers both sensible and latent heat (moisture). Use HRV in cold, dry climates where humidity control isn't needed. Use ERV in humid climates or where maintaining indoor humidity is important.

Size based on larger of: (1) ASHRAE 62.2 continuous ventilation rate = 3.5 L/s + 0.35 L/s per m² floor area, or (2) 0.5 ACH of total home volume. A 200 m² home needs approximately 75-100 L/s (150-200 m³/h). Add capacity for boost mode in kitchens/bathrooms (2-3× base rate).

Sensible heat recovery efficiency = (T_supply - T_outdoor) / (T_exhaust - T_outdoor) × 100%. Good units achieve 75-90%. At -20°C outdoor with 20°C indoor, 80% efficiency means supply air enters at 12°C instead of -20°C. Higher efficiency means less supplemental heating needed.

Install the main unit in a utility room, basement, or attic with access for filter maintenance. Exhaust from bathrooms, kitchen, and utility rooms. Supply to bedrooms and living areas. Balance supply and exhaust flows. Insulate all ductwork in unconditioned spaces. Include condensate drain for the heat exchanger.

Clean or replace filters every 1-3 months depending on air quality. Clean heat exchanger core annually—most can be removed and washed. Check condensate drain for blockages. Verify fan operation and balance. Clean or vacuum intake/exhaust hoods. Annual professional inspection recommended.

Learn More

Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) are mechanical ventilation systems recovering thermal energy from exhaust air to precondition incoming outdoor air, significantly reducing heating and cooling loads associated with ventilation while maintaining acceptable indoor air quality. These systems are essential in energy-efficient building design, particularly in climates with extreme temperatures where conditioning outdoor air cost is substantial. HRVs and ERVs provide continuous balanced ventilation (equal supply and exhaust airflows), replacing uncontrolled infiltration and exfiltration with controlled, filtered, energy-efficient outdoor air delivery.

HRV vs. ERV Distinction: HRVs transfer only sensible heat (temperature) between exhaust and outdoor air streams using aluminum or plastic plate heat exchangers allowing thermal conduction but preventing moisture transfer. Ideal for cold, dry climates where indoor humidity control is desired during winter—HRV prevents moisture from humid indoor air transferring to dry incoming outdoor air, maintaining comfortable humidity levels. ERVs transfer both sensible and latent heat (moisture) using desiccant-coated enthalpy wheels or permeable membranes transferring water vapor with temperature. Preferred in hot-humid climates (summer dehumidification benefit) and spaces with high indoor moisture generation (bathrooms, kitchens, swimming pools) where moisture recovery during winter reduces excessive dryness.

Heat Exchanger Effectiveness and Types: Sensible effectiveness εs measures temperature recovery: εs = (Tsupply - Toutdoor) / (Texhaust - Toutdoor). For ERVs, total effectiveness εt includes both sensible and latent recovery. Residential HRVs typically achieve 60-75% sensible effectiveness, high-performance units 80-90%, best passive house systems exceed 90%. Commercial ERVs range 65-80% total effectiveness. Heat exchanger types include: counter-flow plate (80-95% effectiveness, highest performance, common in passive house), cross-flow plate (60-75%, lower cost, standard residential), rotary enthalpy wheels (70-85%, widely used commercial ERVs), heat pipes/run-around coils (50-65%, useful when ducts not adjacent), and fixed plate ERVs with permeable membranes (65-75%, no moving parts). Higher effectiveness means greater energy recovery but also higher first costs, larger space requirements, and increased pressure drop.

Sizing and Energy Savings: Size HRVs/ERVs per ASHRAE 62.2 residential (Qtot = 0.15 × Afloor + 3.5 × (Nbr + 1)) or ASHRAE 62.1 commercial ventilation rate procedure. Example: 185m², 3-bedroom home requires 41.75 L/s (89 CFM), add 10-15% for duct losses, select HRV rated 45-50 L/s. Commercial units range 500-50,000 CFM. Proper sizing avoids undersizing (inadequate ventilation, IAQ problems) and oversizing (excessive first cost, poor part-load efficiency). Energy savings substantial—residential system with 45 L/s, 75% effectiveness, 30°C winter temperature difference recovers 1,218W continuous heating (6,090 kWh annually). Subtracting fan power (50-80W) and maintenance, net annual energy savings 5,500-6,000 kWh. Energy recovery periods typically range 2.6-7.5 years. Commercial buildings with higher ventilation rates have shorter recovery periods (2-5 years).

Frost Control and ASHRAE 90.1 Requirements: When outdoor air below -10°C to -25°C, moisture condenses and freezes on cold side of heat exchanger, blocking airflow and reducing effectiveness. Frost control strategies include defrost cycles (periodically close outdoor damper, run exhaust through both sides to melt ice, 5-10 minutes every 30-60 minutes when <-15°C), preheating outdoor air (electric/hydronic coil), recirculating warm supply air, or modulating airflow. High-performance passive house HRVs operate effectively to -30°C or colder. ASHRAE 90.1 Section 6.5.6.1 mandates energy recovery for systems exceeding thresholds varying by climate zone and percent outdoor air—Climate Zone 3B requires ERV if outdoor air >70% of supply and capacity >11,000 L/s; Climate Zone 6A requires ERV if outdoor air >30% of supply and capacity >2,350 L/s.

Control Integration and Maintenance: Demand-controlled ventilation using CO₂ sensors modulates fan speed based on occupancy, reducing ventilation during low-occupancy periods (saving fan energy). Economizer lockout disables energy recovery when outdoor conditions favorable for free cooling, allowing 100% outdoor air bypass. Schedule-based control reduces ventilation to code minimums during unoccupied hours. Airflow balancing maintains equal supply and exhaust flows (±5-10%) ensuring neutral building pressure and optimal heat exchanger performance. Maintenance includes regular filter changes (3-6 months residential, 1-3 months commercial), heat exchanger core cleaning (annually residential, semi-annually commercial), condensate drain inspection, and fan inspection. HRV/ERV lifespan typically 15-25 years with proper maintenance.

Standards Reference: ASHRAE 62.2 specifies residential ventilation requirements. ASHRAE 62.1 governs commercial ventilation. ASHRAE 90.1 Section 6.5.6.1 mandates energy recovery for specific applications by climate zone and system capacity. Passive House Institute (PHI) certification requires ventilation heat recovery efficiency ≥\geq75% for extreme climates.

Passive House - High-Performance Residential HRV

Size HRV for passive house with continuous balanced ventilation and superior heat recovery

1
Floor Area: 185 m²
2
Occupants: 4
3
Ceiling Height: 2.6 m
4
Air Tightness: 0.6 ACH@50Pa
5
Heat Recovery Efficiency: 85%

Result

Required HRV capacity:
150 m³/h

Calculations

  • •
    Building volume: 185m² × 2.6m = 481 m³
  • •
    ASHRAE 62.2 ventilation rate: 0.15 L/s/m² × 185m² + 3.5 L/s/person × 4 = 41.75 L/s = 150 m³/h minimum
  • •
    Passive House standard 0.3 ACH = 481m³ × 0.3 = 144 m³/h
  • •
    Select larger value: 150 m³/h rated capacity

Energy Savings

  • •
    Without HRV: Heating outdoor air -10°C to 20°C requires Q=150×1.2×1.005×30/3.6=1,506Q = 150 \times 1.2 \times 1.005 \times 30 / 3.6 = 1{,}506 W continuous
  • •
    With 85% efficient HRV: Heat recovered 1,280W, supplemental heating 226W (85% energy savings)
  • •
    Annual savings: 1,280W × 5,000 heating degree hours = 6,400 kWh/year recovered

Equipment

  • •
    Zehnder ComfoAir 200 or equivalent: 150-250 m³/h capacity (boost mode for kitchen/bathroom)
  • •
    Counter-flow aluminum heat exchanger (no cross-contamination, frost protection to -25°C)
  • •
    EC motors 30-60W, sound level below 25 dB(A)

Installation

  • •
    Ductwork 100-125mm insulated semi-rigid to supply grilles (bedrooms, living) and return grilles (bathrooms, kitchen)
  • •
    Duct runs below 15m minimize pressure drop

Controls

  • •
    Continuous low speed (0.3 ACH background)
  • •
    Boost button (0.5-0.7 ACH for moisture/odor, 20-30 min timer)
  • •
    Optional CO₂ sensor for demand-controlled ventilation

Financial

  • •
    Energy recovery period: 3.6-5.5 years

Additional Notes

Per ASHRAE 62.2, HRV size based on required ventilation rate: typically 50-200 CFM residential (0.35 air changes per hour). Effectiveness: 60-85% sensible heat recovery typical for residential units, 70-90% for commercial. Higher effectiveness reduces heating/cooling penalty but costs more. Install in unconditioned space (basement/mechanical room), duct outdoor air intake away from exhausts, balance airflows (supply = exhaust ±10%).

Commercial Office - ERV with Demand Control Ventilation

Size ERV for commercial office with variable occupancy and energy-efficient demand-controlled ventilation

1
Floor Area: 850 m²
2
Occupants: 80
3
Ceiling Height: 2.8 m
4
Heat Recovery Efficiency: 75%
5
Ventilation Standard: ASHRAE 62.1

Result

Required ERV capacity:
1,600 m³/h

Calculations

  • •
    ASHRAE 62.1 ventilation: 0.3 L/s/m2×850 m2+2.5 L/s/person×80=455 L/s=1,638 m3/h0.3 \text{ L/s/m}^2 \times 850 \text{ m}^2 + 2.5 \text{ L/s/person} \times 80 = 455 \text{ L/s} = 1{,}638 \text{ m}^3/\text{h}
  • •
    With 15% diversity factor (hybrid work): 1,392 m³/h average demand
  • •
    Specify 1,600 m³/h capacity (allows peak occupancy + filtration pressure drop)

Controls (DCV)

  • •
    6 CO₂ sensors distributed across open office (one per 140 m² zone)
  • •
    BAS modulates fan speed 40-100% to maintain CO₂ below 1,000 ppm
  • •
    Low occupancy: 600-800 m³/h (40-50% speed)
  • •
    High occupancy: 1,600 m³/h (100% speed)
  • •
    Annual average 65% speed = 27% fan energy (cubic law)

Energy Savings

  • •
    Heating season (180 days): 12.6 kW load, 75% recovered = 2,227 USD/year savings
  • •
    Cooling season (120 days): 18.0 kW load (sensible + latent), 75% recovered = 4,212 USD/year savings
  • •
    Fan energy cost: 263 USD/year
  • •
    Net annual savings: 6,176 USD/year

Equipment

  • •
    Daikin or Carrier ERV unit 1,600 m³/h (rotating enthalpy wheel 75% effectiveness)
  • •
    EC motors VFD-controlled, MERV 11 supply / MERV 8 exhaust filters
  • •
    6× Veris or Telaire CO₂ sensors (0-2,000 ppm, ±50 ppm accuracy)
  • •
    Tridium Niagara or Johnson Controls BAS integration
  • •
    450mm diameter supply/exhaust ductwork through ceiling plenum

Financial

  • •
    Installed cost: 28,000-38,000 USD (ERV 18,000-24,000 + sensors/BAS 4,500-6,500 + ductwork 5,500-7,500)
  • •
    Simple payback: 3.6 years (22,000 USD premium / 6,176 USD/year)
  • •
    20-year lifecycle benefit: 123,520 USD (PV @ 4%: 84,000 USD)
  • •
    ROI: 282%

Additional Notes

Commercial HRV/ERV systems per ASHRAE 90.1 mandatory in climate zones with >5000 HDD or CDD for systems >5000 CFM outdoor air. ERV (energy recovery ventilator) transfers both sensible and latent heat—recommended for humid climates or moisture-generating spaces. Sizing: Match required outdoor air per ASHRAE 62.1. Control integration: Modulate with building occupancy, lockout during economizer operation. Maintenance: Replace filters quarterly, clean heat exchanger cores annually.

School Building - High-Capacity ERV with IAQ Monitoring

Design large-capacity ERV system for K-12 school with enhanced IAQ monitoring and code-compliant ventilation rates

1
Floor Area: 2,400 m²
2
Occupants: 525
3
Ceiling Height: 3.2 m
4
Heat Recovery Efficiency: 80%
5
Ventilation Standard: ASHRAE 62.1

Result

Required ERV capacity:
10,500 m³/h

Calculations

  • •
    ASHRAE 62.1 ventilation: 0.3 L/s/m2×2,400 m2+4.0 L/s/person×525=2,820 L/s=10,152 m3/h0.3 \text{ L/s/m}^2 \times 2{,}400 \text{ m}^2 + 4.0 \text{ L/s/person} \times 525 = 2{,}820 \text{ L/s} = 10{,}152 \text{ m}^3/\text{h}
  • •
    Higher occupant rate (4.0 vs 2.5 L/s/person) for children's metabolic rate
  • •
    Specify 10,500 m³/h (margin for filtration and future growth)

Equipment

  • •
    Two parallel ERV units (5,250 m³/h each, N+1 redundancy)
  • •
    Rotating enthalpy wheel 80% effectiveness, EC motors 7.5 kW each
  • •
    VFD modulation 50-100% speed, MERV 13 supply / MERV 8 exhaust filters
  • •
    N+1 allows 50% operation if one unit fails (avoids school closure)

IAQ Monitoring

  • •
    40 sensors total (2 per classroom × 20 classrooms)
  • •
    Each measures: CO₂ (0-2,000 ppm), VOC (0-5,000 ppb), PM2.5 (0-500 μg/m³), temp, RH
  • •
    Johnson Controls Metasys or Siemens Desigo BAS integration
  • •
    Real-time dashboards for facility management and parent transparency

Controls

  • •
    Pre-occupancy (6-7 AM): 50% speed for building purge
  • •
    Occupied hours (7 AM-3:30 PM): 70-100% modulated by CO₂ sensors
  • •
    After-hours (3:30-5 PM): 30% for custodial staff
  • •
    Off 5 PM-6 AM (no occupancy)
  • •
    Annual average 72% speed = 37% fan energy (cubic law)

Energy Savings

  • •
    Heating (180 days, 1,800 hr): 111.5 kW load, 80% recovered = 10,008 USD/year
  • •
    Cooling (90 days, 900 hr): 101.6 kW load (sensible + latent), 80% recovered = 10,242 USD/year
  • •
    Fan energy: 2,797 USD/year
  • •
    Net annual savings: 17,453 USD/year

Financial

  • •
    Installed cost: 185,000-245,000 USD (ERV units 110,000-145,000 + IAQ sensors 28,000-38,000 + BAS 22,000-32,000 + ductwork 25,000-30,000)
  • •
    ERV premium vs ventilation-only: 95,000-125,000 USD
  • •
    Simple payback: 6.3 years (within 10-15 year district threshold)
  • •
    20-year lifecycle benefit: 349,060 USD (PV @ 3%: 260,000 USD)
  • •
    ROI: 136%

Health Benefits

  • •
    Lower CO₂ below 950 ppm improves cognitive performance +10-15% (Harvard studies)
  • •
    Reduced absenteeism 15-25% (CDC K-12 guidance)
  • •
    MERV 13 removes allergens and respiratory droplets
  • •
    Meets ASHRAE 241 Infection Risk Management Mode

Additional Notes

Industrial HRVs for process ventilation recover heat from high-temperature exhaust streams. Rotary heat exchangers: 75-85% effectiveness, handle large airflows (>50,000 CFM). Plate exchangers: No cross-contamination between air streams (required for labs, food processing). Run-around loops: Allow separated supply/exhaust locations. Size based on: exhaust temperature (efficiency decreases at higher temps), airflow balance (exhaust typically >supply to maintain slight negative pressure). Fouling potential (process exhaust may require frequent cleaning).

ASHRAE 62.1 - Ventilation for Acceptable Indoor Air Quality

ASHRAE 62.1-2022 (2022)

ASHRAEstandard

ASHRAE 90.1 - Energy Standard for Buildings

ASHRAE 90.1-2022 (2022)

ASHRAEstandard

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