ASHRAE 62.2-2022 Formula
ASHRAE Standard 62.2 is the residential ventilation standard adopted by the IECC and most building codes. The required whole-house outdoor air rate is Q = 0.03 × A + 7.5 × (N+1), where A is the conditioned floor area in square feet and N is the number of bedrooms. The first term covers contaminants that scale with building size (off-gassing, cooking, cleaning); the second term covers contaminants that scale with occupancy (CO2, moisture, odors) assuming one more person than bedrooms.
HRV vs ERV
A Heat Recovery Ventilator (HRV) transfers sensible heat between the incoming fresh air and outgoing stale air streams without mixing them. It pre-warms incoming winter air and pre-cools summer air but does not affect humidity. HRVs work well in dry climates and in homes where winter humidity is very low. An Energy Recovery Ventilator (ERV) also transfers latent heat (moisture) across the core. In humid summers it keeps some humidity outside; in dry winters it retains indoor humidity. ERVs are preferred in climates with any significant humidity load — which includes most of the continental US outside the arid southwest.
Infiltration Credit
If you have a blower door test result (ACH50), you can deduct some credit for natural infiltration. Convert ACH50 to natural ACH using the LBL normalization factor: natural ACH ≈ ACH50 ÷ NF, where NF is typically 15 (mild climate, single-story) to 20 (cold climate, multi-story). A 2,000 sq ft 3-bedroom house with 5 ACH50 and 16,000 cu ft volume gets natural ACH ≈ 5/17 ≈ 0.29, giving Q_inf ≈ 78 CFM. That is nearly enough to meet the 90 CFM total requirement without any mechanical ventilation — but only if the leakage is evenly distributed and the building is breathable year-round.
Kitchen and Bath Exhaust
ASHRAE 62.2 also requires local exhaust at moisture sources: 100 CFM intermittent or 25 CFM continuous in kitchens, and 50 CFM intermittent or 20 CFM continuous in bathrooms. These are separate from the whole-house rate and should be calculated per space. A well-sealed house should run continuous low-speed bath exhaust to remove moisture from showers without needing to remember to turn fans on.
ASHRAE 62.2-2022 Required CFM Table
Whole-house mechanical ventilation rate by floor area and number of bedrooms, before any infiltration credit:
| Floor area | 1 bed | 2 bed | 3 bed | 4 bed | 5 bed |
|---|---|---|---|---|---|
| 1,000 sq ft | 45 CFM | 52.5 | 60 | 67.5 | 75 |
| 1,500 sq ft | 60 | 67.5 | 75 | 82.5 | 90 |
| 2,000 sq ft | 75 | 82.5 | 90 | 97.5 | 105 |
| 2,500 sq ft | 90 | 97.5 | 105 | 112.5 | 120 |
| 3,000 sq ft | 105 | 112.5 | 120 | 127.5 | 135 |
| 4,000 sq ft | 135 | 142.5 | 150 | 157.5 | 165 |
Popular ERV/HRV models that fit these ranges: Panasonic Intelli-Balance 100 (30-120 CFM), Fantech VHR 704 (50-200 CFM), Zehnder ComfoAir Q350 (70-205 CFM), Broan AI Series (50-160 CFM). Size at 100-120% of calculated need so the unit runs at a middle-speed setpoint rather than maxed out.
Frequently Asked Questions
Do I need mechanical ventilation in an old leaky house?
Probably not — infiltration alone meets the 62.2 rate in most 1960s-1990s homes. Modern tight houses (post-2015 IECC) always do.
What is the normalization factor NF?
A LBL model factor that converts pressure-test ACH50 to real-world natural ACH. 17 is average; use 15 in warm climates, 20 in cold multi-story.
Can I use a bathroom fan for whole-house ventilation?
Yes — if it is rated for continuous operation (≤1.5 sones, ECM motor) and runs 24/7 at the required CFM.
How do I hit 90 CFM with an ERV?
Most residential ERVs provide 40-200 CFM at different speeds. Set the ERV to the boost speed that matches your required mechanical CFM.
Does ASHRAE 62.2 apply to apartments?
Yes — it applies to any dwelling unit, including condos, apartments, and attached townhouses.
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