You will understand how to calculate ventilation for ASHRAE 62.2-2013.
Local Exhaust (Spot Ventilation)
Bathrooms: 50āÆCFM (intermittent) or 20āÆCFM (continuous)
Kitchens: 100āÆCFM (intermittent) or 5āÆACH continuous
(turn0search7)
Local fans count toward whole-house requirements, so you can “double-dip” them.
WholeāHouse Ventilation
The total required outdoor airflow (Qtot) is calculated via:
Qtot = 0.03 Ć Afloor + 7.5 Ć (Nbr + 1) [in CFM]
Afloor = floor area (ftĀ²)
Nbr = number of bedrooms (at least 1)
In metric: Qtot = 0.15 Ć Afloor(mĀ²) + 3.5 Ć (Nbr + 1) L/s
Accounting for Infiltration
If a blower-door test is done, infiltration credit (Qinf) is subtracted:
Qfan = Qtot ā Qinf
Qfan = mechanical ventilation needed
Qinf = infiltration credit (from multi-point tests via ASTM E779 or CGSB)
Qinf may not exceed ā of Qtot for new construction
Final Mechanical Ventilation Rate
Continuous systems: supply/run fan at Qfan CFM continuously.
Intermittent systems: Qon (on-cycle rate) is determined so that average ventilation meets Qfan, adjusted using factors from Table 4.2
Example Calculation
For a 2,400āÆftĀ² home with 3 bedrooms:
Qtot = 0.03 Ć 2400 + 7.5 Ć (3 + 1) = 72 + 30 = 102āÆCFM
Suppose infiltration test yields Qinf = 30āÆCFM
Required mechanical is Qfan = 102āÆāāÆ30 = 72āÆCFM
An intermittent system running 50% of the time would operate at ~144āÆCFM to average 72āÆCFM ventilation.
Why It Matters
Combines continuous area-based and occupant-based ventilation methods.
Offers infiltration creditsāwhen validated by blower-door testingāto potentially reduce mechanical load.
Accommodates continuous or intermittent systems, including local exhaust offsets.
Clearly defined in ASHRAE Standard 62.2ā2013 Sections 4.1ā4.5, with comprehensive guidance on credits, system types, and intermittent operation.
