HRV / ERV Effectiveness Calculator — Free Online Calculator
Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) pre-condition incoming fresh air using energy from the exhaust stream. Effectiveness — the fraction of maximum possible heat transfer actually achieved — is the key performance metric under ASHRAE Standard 84. Enter supply and exhaust airflow rates and temperatures to calculate sensible effectiveness and detect flow-imbalance problems instantly.
Enter airflow and temperatures
Sensible Effectiveness
Vmin
—
Flow Balance
—
Rating
—
Warning
See the breakdown
Effectiveness calculated per ASHRAE Standard 84. Balanced flow (|Vs−Ve|/max ≤ 10%) is required for a valid effectiveness reading.
HRV/ERV effectiveness benchmarks
Sensible effectiveness at rated conditions (balanced flow, ASHRAE 84 test method).
| Sensible Effectiveness | Rating | Typical product type |
|---|---|---|
| Under 65% | Basic | Low-cost plate exchanger |
| 65–75% | Standard | Entry-level rotary wheel or plate |
| 75–82% | Good | Mid-range cross-flow or counter-flow plate |
| 82–90% | Excellent | High-efficiency counter-flow or rotary |
| 90%+ | Premium | High-performance rotary wheel with purge sector |
The effectiveness formula, explained
ASHRAE Standard 84 defines sensible heat recovery effectiveness as the ratio of heat actually transferred between supply and exhaust streams to the maximum heat that could be transferred if the streams reached thermal equilibrium. The minimum airflow rate (Vmin) is used as the denominator because it represents the limiting stream — the smaller flow has the shorter contact time and therefore controls the maximum possible transfer.
Why use Vmin?
The smaller of supply and exhaust flows is always the limiting stream. Using total flow would overstate effectiveness when the streams are imbalanced.
HRV vs ERV
An HRV transfers sensible heat only (air temperature). An ERV transfers both sensible heat and moisture (latent energy), making it better suited for humid climates where dehumidification is valued.
Flow balance matters
ASHRAE 84 specifies testing at balanced flow. An imbalance above 10% distorts the measured effectiveness and can cause building pressurisation problems — positive pressure in heating-dominated climates risks moisture drive into wall assemblies.
ASHRAE 62.2 context
HRVs and ERVs are often sized to meet ASHRAE 62.2 whole-building ventilation rates. The effectiveness calculator here verifies equipment performance; for required CFM targets, use the Ventilation Calculator.
Worked examples
Three scenarios covering a typical residential unit, a flow-imbalance warning, and a premium rotary ERV.
Balanced residential HRV — 150 CFM each, t₁=20°F, t₂=58°F, t₃=70°F
Result: 76% sensible effectiveness — typical for a mid-range plate exchanger in cold-climate heating season.
Imbalanced unit — supply 200 CFM, exhaust 140 CFM (same temps)
Warning triggers: "Unbalanced flow rate: Volumetric supply and exhaust imbalance exceeds 10%. This will distort apparent thermal effectiveness and risk building pressure issues."
High-performance rotary ERV — 100 CFM balanced, t₁=10°F, t₂=64°F, t₃=70°F
Result: 90% — premium-tier rotary wheel performance confirmed.
Frequently asked questions
Common questions about HRV and ERV effectiveness and ASHRAE 84.
What is HRV effectiveness?
HRV sensible effectiveness is the percentage of maximum possible sensible heat transfer that the unit actually achieves between supply and exhaust airstreams, measured per ASHRAE Standard 84. A unit with 80% effectiveness pre-conditions 80% of the temperature difference between indoor and outdoor air, reducing the heating or cooling load on the main HVAC system.
What is the difference between HRV and ERV?
An HRV (Heat Recovery Ventilator) transfers sensible heat only — it pre-conditions the temperature of incoming air. An ERV (Energy Recovery Ventilator) transfers both sensible heat and moisture (latent energy), recovering humidity in winter and limiting humidity gain in summer. ERVs are generally preferred in climates with high latent loads; HRVs are preferred where moisture recovery could cause condensation problems.
What is a good HRV effectiveness rating?
Most residential HRVs achieve 70–85% sensible effectiveness at rated conditions. ENERGY STAR requires a minimum 55% for HRVs; premium counter-flow and rotary-wheel units exceed 90%. Higher effectiveness reduces ventilation-related heating and cooling costs but generally increases equipment cost.
Why does flow balance matter for HRV/ERV?
ASHRAE Standard 84 requires balanced supply and exhaust flows for a valid effectiveness test. An imbalance above 10% distorts the measured effectiveness reading. Operationally, a persistently unbalanced HRV will either pressurise or depressurise the building, affecting infiltration rates, moisture drive through the envelope, and combustion appliance safety.
What ASHRAE standard covers HRV/ERV testing?
ASHRAE Standard 84 — Method of Testing Air-to-Air Heat/Energy Exchangers — defines the effectiveness measurement method, test conditions, and minimum airflow balance requirements. ASHRAE 62.2 and 62.1 govern the ventilation rates that HRVs and ERVs are often sized to meet.
Can effectiveness exceed 100%?
Under ASHRAE 84, sensible effectiveness above 95% is flagged as a thermodynamic anomaly under practical steady-state conditions. Apparent readings above 100% always indicate a measurement error, a condensation effect boosting the apparent reading, or sensor calibration problems.
Confirmed the effectiveness. Now build the ventilation quote.
Equipment performance data gives you the scope — TradesQuote converts it into a detailed, line-item estimate in seconds. Describe the ventilation job or upload photos, and the AI builds quantities, unit prices, and totals, validated by a built-in quality control agent.
AI line-item estimates
Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
Shareable & signable
Clients review, accept, and sign from a public link.
No credit card required · 14-day free trial · Cancel anytime
More HVAC calculators
Ventilation Calculator
ASHRAE 62.2 residential and 62.1 commercial ventilation CFM.
CFM / Airflow Calculator
Room airflow and system total CFM targets.
Humidity Control Calculator
Humidifier and dehumidifier sizing from latent load.
Sensible & Latent Heat Calculator
Split total coil load into sensible and latent BTU/h.