ERV Sizing Calculator
Energy recovery ventilators (ERVs) and heat recovery ventilators (HRVs) provide controlled fresh air to tight homes while recovering most of the energy in the exhaust air stream. ASHRAE Standard 62.2 specifies the minimum whole-house ventilation rate for residential buildings: total required CFM = 0.01 times conditioned floor area plus 7.5 times the number of occupants (estimated as bedrooms plus one). An optional blower-door-tested infiltration credit can reduce the required mechanical ventilation when significant natural air leakage is present. Select an ERV or HRV rated at or above the calculated CFM at your duct pressure conditions.
ASHRAE 62.2 ventilation formula
Gross CFM = 0.01 × floor area (sq ft) + 7.5 × (bedrooms + 1)
Infiltration credit (CFM) = 0.03 × ACH50 × floor area / 60 (ASHRAE 62.2-2022 simplified)
Net mechanical CFM = max(0, Gross CFM − infiltration credit)
ASHRAE 62.2 uses bedrooms + 1 as an occupant proxy (a two-bedroom home has an assumed occupancy of 3). The infiltration credit calculation here is a simplified version of Annex A in ASHRAE 62.2-2022; the full calculation also depends on climate zone and house volume. When ACH50 is not known, enter 0 for no infiltration credit (conservative). Size the ERV or HRV at or above the net mechanical CFM at the unit's rated external static pressure.
ERV vs HRV selection guidance
- Cold, dry climates (IECC Zone 5-7): use an HRV to transfer only sensible heat, keeping indoor humidity levels higher in winter.
- Hot, humid climates (IECC Zone 1-3): use an ERV to prevent excess moisture from entering with fresh air during summer.
- Mixed climates (IECC Zone 4): either works; an ERV is often preferred for year-round moisture management.
- Size the unit at rated CFM at 0.40 in. w.c. external static pressure, a typical value for balanced ERV/HRV duct connections.
- A balanced ventilation system (equal supply and exhaust) is preferred over exhaust-only or supply-only because it avoids depressurizing or pressurizing the house and maintains more controlled air distribution.
ERV sizing: frequently asked questions
What is ASHRAE 62.2 and why does it matter for ERV sizing?
ASHRAE Standard 62.2 (Ventilation and Acceptable Indoor Air Quality in Residential Buildings) establishes the minimum whole-house mechanical ventilation rate required to maintain healthy indoor air quality. The 2022 edition formula is: CFM = 0.01 x floor area + 7.5 x (bedrooms + 1). Many state energy codes (including IECC) reference ASHRAE 62.2 compliance for new construction.
What is the difference between an ERV and an HRV?
A heat recovery ventilator (HRV) transfers only sensible heat between exhaust and supply air streams. An energy recovery ventilator (ERV) transfers both sensible heat and moisture (latent heat). HRVs are preferred in cold, dry climates where you want to prevent indoor humidity from being exhausted. ERVs are preferred in hot, humid climates to limit moisture introduced by fresh air.
Does my new home need an ERV?
Modern energy codes require homes to meet a minimum air tightness standard, and many jurisdictions require mechanical ventilation when air leakage is below a certain threshold. The 2021 IECC requires whole-house mechanical ventilation for homes tested at or below 5 ACH50. An ERV or HRV is the most energy-efficient way to meet this requirement while minimizing heating and cooling penalties.
How do I account for infiltration credit in ASHRAE 62.2?
ASHRAE 62.2-2022 allows a credit for natural infiltration measured by blower door test. The infiltration credit = 0.03 x ACH50 x floor area (for homes tested below a threshold). Subtract this from the required ventilation CFM. Tighter homes have lower infiltration credits and thus need more mechanical ventilation.
What is the typical efficiency of an ERV or HRV?
Most residential ERVs have sensible heat exchange efficiency of 70 to 85% and total energy (sensible plus latent) efficiency of 60 to 75%. High-efficiency counterflow core units reach 80 to 90% sensible efficiency. Higher efficiency reduces the energy penalty for ventilation; in cold climates, a 75% efficient HRV saves 75% of the heating energy compared to direct outdoor air ventilation.
Official sources
- ASHRAE: ASHRAE Standard 62.2 (Ventilation for Acceptable Indoor Air Quality in Residential Buildings).
- U.S. DOE Energy Saver: Heat Recovery Ventilators and Energy Recovery Ventilators.
- ICC / IECC: International Energy Conservation Code (ventilation requirements).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.