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ERV/HRV Sizing Calculator

Estimate the required continuous ventilation rate (CFM) for a whole-house ERV or HRV, per the ASHRAE 62.2 formula.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Required continuous ventilation rate

78.44 CFM (continuous)

High confidence

This is the standard ASHRAE 62.2 formula for continuous whole-house mechanical ventilation — actual equipment selection should also account for your specific ERV/HRV unit's rated efficiency and any local code amendments to the base ASHRAE formula.

House area
1614.59 sq ft

With the figures above, the required continuous ventilation rate comes to 78.4 CFM (continuous). This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 78.438 CFM (continuous) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • ASHRAE 62.2 whole-house mechanical ventilation formula: required CFM = 0.03 x floor area (sq ft) + 7.5 x (number of bedrooms + 1)

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Frequently asked questions

Why does a tight, energy-efficient home need mechanical ventilation?
Air-sealing and insulation improvements reduce the incidental fresh air that used to leak in through gaps — without deliberate mechanical ventilation, indoor air quality, humidity, and odor control can suffer in a very tight home.
What's the difference between an ERV and an HRV?
Both recover heat from outgoing air to precondition incoming fresh air, saving energy — an ERV (energy recovery ventilator) also transfers some humidity between the airstreams, which is often preferred in humid climates or homes needing humidity control, while an HRV (heat recovery ventilator) transfers heat only.
Is this rate required to run continuously?
ASHRAE 62.2 is designed as a continuous (24/7) ventilation rate, though some systems use intermittent operation at a higher rate to average out to the same total air exchange — check your specific system's control strategy.