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18
March
ASHRAE 62.2-2025: Comprehensive Overview & Practical Guidance (For Residential IAQ & Ventilation)
ASHRAE 62.2-2025: Comprehensive Overview & Practical Guidance (For Residential IAQ & Ventilation)
As homes become more energy-efficient and airtight, ANSI/ASHRAE Standard 62.2-2025 is the go-to benchmark for ensuring acceptable indoor air quality (IAQ) through mechanical ventilation, local exhaust, and source control. This edition (incorporating 16 addenda from the 2022 version) raises the bar for health-focused design.
Core Purpose & Scope:
1. Apply to single-family homes, townhouses, and low-rise multifamily dwellings (non-transient occupants).
2. Minimum requirements for dwelling-unit ventilation, local mechanical exhaust, and source control to dilute contaminants from occupants, materials, and activities.
3. Not maximum higher rates are encouraged for better IAQ, especially during pollution episodes or health concerns.
Key Updates in 2025 Edition
From official ASHRAE sources:
1. Filtration upgrade: Systems with mechanical supply now require MERV 11 filters (up from MERV 6) better capture of fine particles (1-3 microns), allergens, and pollutants.
2. New optional IAQ Procedure: Performance-based compliance path for innovative designs (modeling, measurements, or alternatives to prescriptive rates).
3. Local exhaust expansion: Now explicitly required in toilet rooms (in addition to kitchens and bathrooms).
4. Ozone limits: Air-cleaning devices (e.g., electronic cleaners) must not generate excessive ozone.
5. Duct sizing change: Uses equivalent diameter (instead of hydraulic) for prescriptive tables -simplifies calculations.
6. Ground cover requirement: Exposed earth in crawlspaces must be covered to limit soil gas entry (radon, moisture).
7. Shorter separation distance exception: Reduced minimum between air intakes and exhausts under specific conditions.
8. Infectious aerosol guidance: New informative Appendix E (references ASHRAE 241) - boost ventilation, upgrade to MERV 13, if possible, maintain 40–60% humidity, use portable HEPA cleaners during outbreaks.
Whole-Building Ventilation Rate Calculation
Formula (I-P units): Qfan = 0.03 × Afloor + 7.5 × (Nbr + 1) [cfm]
Afloor = conditioned floor area (ft²)
Nbr = number of bedrooms
ASHRAE 62.2 Infiltration Credit
1. Ventilation Equation:
Qfan=Qtot-Qinf(balanced systems).
2. Infiltration Rate (Qinf):
Qinf=0.052x Q50 x wsf x (H/Hr)z
Q50: blower door leakage at 50 Pa
wsf: weather/shielding factor
H: ceiling height, Hr=8.2 ft
z: exponent (≈0.65–0.75)
System Type:
1. Balanced (HRV/ERV): full credit (Φ = 1).
2. Unbalanced (exhaust/supply): reduced credit.
Requirement: Blower door test mandatory; no default assumptions.
Local Exhaust Requirements:
1. Kitchen: 100 cfm intermittent or 5 ACH continuous (ducted outdoors).
2. Bathroom/Toilet: 50 cfm intermittent or 20 cfm continuous (each room, ducted outdoors).
