What is the ASHRAE 62.2 formula for residential ventilation?

ASHRAE 62.2 requires Qfan = 0.01 × Afloor + 7.5 × (Nbr + 1), where Afloor is the conditioned floor area in sq ft and Nbr is the number of bedrooms. A 2,000 sq ft home with 3 bedrooms needs 0.01×2000 + 7.5×4 = 50 CFM minimum.

How do I calculate commercial ventilation with ASHRAE 62.1?

ASHRAE 62.1 Ventilation Rate Procedure: Vbz = Rp×Pz + Ra×Az, where Rp is the per-person rate (cfm/person), Pz is occupancy, Ra is the area rate (cfm/sf), and Az is the zone area. Divide by zone air distribution effectiveness Ez to get the outdoor air intake flow Voz.

What does ACH mean in ventilation?

ACH stands for Air Changes per Hour — the number of times the total air volume of a space is replaced with fresh outdoor air per hour. It equals (CFM × 60) ÷ Volume(ft³). ASHRAE recommends 0.35 ACH minimum for residences and higher rates for commercial spaces.

Ventilation Rate Calculator

ASHRAE 62.1 & 62.2 — Calculate required CFM, air changes per hour, and outdoor air loads for residential and commercial spaces

Building Type

ASHRAE 62.2 — Residential

Floor Area

ft²

Bedrooms

Ceiling Height

Stories

floors

ASHRAE 62.1 — Ventilation Rate Procedure

Occupancy

people

Floor Area

ft²

Ceiling Height

Distribution Ez

Space type rates: loading…

Energy & Cost

Energy Rate

$/kWh

Design ΔT

°F

Required Ventilation

CFM outdoor air

Area component (0.01 × ft²) —

Occupancy component (7.5 × (Nbr+1)) —

Rp (cfm/person) —

Ra (cfm/ft²) —

Vbz = Rp×Pz + Ra×Az —

Voz = Vbz ÷ Ez —

—

Air Changes/hr (ACH)

—

Space Volume (ft³)

—

CFM per Person

—

CFM per 100 ft²

—

OA HVAC Capacity

—

Est. Energy Cost/yr

📋 ASHRAE 62.2 — Residential

Room-by-Room Ventilation Planner

Add zones/rooms to calculate total required ventilation and compare against existing equipment capacity.

ASHRAE Ventilation Standards Reference

Key tables and guidelines from ASHRAE 62.1-2019 and 62.2-2022.

ASHRAE 62.1 — Table 6-1: Minimum Ventilation Rates (Selected Space Types)

Space Type	Rp (cfm/person)	Ra (cfm/ft²)	Default Occupancy (per 1000 ft²)
Office — Open plan	5	0.06	5
Conference Room	5	0.06	50
Reception / Lobby	5	0.06	30
Retail — Sales floor	7.5	0.12	15
Restaurant — Dining	7.5	0.18	70
Restaurant — Kitchen	7.5	0.12	20
Classroom (K-12)	10	0.12	35
Lecture Hall	7.5	0.06	65
Gym — Spectator area	7.5	0.06	150
Gym — Exercise area	20	0.06	25
Locker Room	10	0.06	10
Healthcare — Patient Room	25	0.06	10
Hotel — Bedroom	5	0.06	10

ASHRAE 62.2 — Residential Formula

Qfan = 0.01 × A_floor + 7.5 × (N_br + 1)
A_floor = conditioned floor area (ft²)
N_br = number of bedrooms
Minimum 1 bedroom assumed (even studios)
Example: 2,000 ft², 3 BR → 0.01×2000 + 7.5×4 = 50 CFM
Applies to single-family homes, townhomes, apartments ≤ 3 stories

ACH Recommendations by Space Type

Residential (bedrooms): 0.35 ACH minimum
Office / open plan: 4–6 ACH
Conference rooms: 6–10 ACH
Classrooms: 4–12 ACH
Restaurants: 8–12 ACH
Gyms / fitness: 6–10 ACH
Hospital patient rooms: 6 ACH minimum
Laboratories: 6–12 ACH (ANSI/AIHA Z9.5)

CO₂ Level Guidelines (IAQ)

Outdoor ambient: ~420 ppm
ASHRAE 62.1 target: < 1,100 ppm (≈ 700 ppm above ambient)
Good air quality: 600–800 ppm
Acceptable: 800–1,000 ppm
Slightly elevated: 1,000–1,400 ppm
Problematic: > 1,400 ppm (consider increasing OA)
OSHA limit (8-hr TWA): 5,000 ppm

Zone Air Distribution Effectiveness (Ez)

Ez = 1.2 — Floor displacement or underfloor air dist.
Ez = 1.0 — Ceiling supply, ceiling return (most systems)
Ez = 0.8 — Ceiling supply with low sidewall return
Ez = 0.8 — Heating systems where supply air < 15°F above zone
Higher Ez = more effective distribution = less OA needed
Source: ASHRAE 62.1 Table 6-2

Outdoor Air Energy Cost Method

OA must be conditioned (heated or cooled) to room temp
Annual heating BTU = CFM × 1.1 × ΔT × HDD × 24
Estimate: ~$8–$18/CFM per year in mixed climates
HRV/ERV reduces OA load by 60–80%
ASHRAE 90.1 mandates heat recovery ≥ 70% where OA > 70% of supply
Energy recovery payback: typically 3–7 years

How to Use This Calculator

Select building type — choose Residential for homes (ASHRAE 62.2) or a commercial type for offices, retail, restaurants, classrooms, and gyms (ASHRAE 62.1).

Enter area and occupancy — for residential enter floor area and bedroom count. For commercial enter occupancy and floor area.

Review the breakdown — the result card shows each formula component (Rp, Ra, Vbz, Voz for commercial; area and occupancy components for residential).

Check ACH — air changes per hour is calculated from the required CFM and the space volume. Verify it falls within recommended ranges.

Estimate energy cost — enter local energy rate and design temperature delta to see approximate annual conditioning cost for outdoor air.

Use Room-by-Room tab — add multiple zones to sum total system requirements and compare to existing equipment capacity.

Key Formulas

ASHRAE 62.2 Residential Qfan = 0.01×A + 7.5×(Nbr+1)

62.1 Breathing Zone OA Vbz = Rp×Pz + Ra×Az

Zone OA Flow Voz = Vbz ÷ Ez

Air Changes per Hour ACH = (CFM × 60) ÷ Volume

Space Volume V = Area × Ceiling Height

OA Conditioning Load BTU/hr = 1.1 × CFM × ΔT

Glossary

CFM — Cubic Feet per Minute. The standard unit of air flow volume used in HVAC design. Required ventilation is expressed in CFM of outdoor air.

ACH — Air Changes per Hour. The number of times the total air volume is replaced per hour. ACH = (CFM × 60) ÷ Volume(ft³).

ASHRAE 62.1 — Standard for ventilation and indoor air quality in commercial, institutional, and high-rise residential buildings.

ASHRAE 62.2 — Standard for low-rise residential buildings. Defines minimum mechanical ventilation using the formula Qfan = 0.01×A + 7.5×(Nbr+1).

Vbz — Breathing Zone Outdoor Airflow. The OA required at occupant level before accounting for distribution effectiveness.

Ez — Zone Air Distribution Effectiveness. A factor (0.8–1.2) reflecting how well the supply air mixes with zone air. Higher is better.

Rp — People outdoor air rate (cfm/person). Accounts for occupant-generated contaminants (CO₂, body odor).

Ra — Area outdoor air rate (cfm/ft²). Accounts for building material off-gassing and surface contaminants.

Frequently Asked Questions

What is the minimum ventilation for a house?

Per ASHRAE 62.2, the minimum is Qfan = 0.01 × floor area (ft²) + 7.5 × (bedrooms + 1). A typical 2,000 ft² 3-bedroom home needs 50 CFM. This can be achieved by a continuously running exhaust fan, supply fan, or balanced HRV/ERV system.

How is commercial ventilation different from residential?

Commercial buildings use ASHRAE 62.1 Ventilation Rate Procedure (VRP). It calculates outdoor air based on both occupancy (Rp × people) and floor area (Ra × ft²), then divides by zone air distribution effectiveness (Ez). Residential 62.2 uses a simpler area-plus-occupancy formula without Ez.

What is a good ACH for an office?

ASHRAE 62.1 targets 4–6 air changes per hour for open-plan offices. Conference rooms often need 6–10 ACH due to higher transient occupancy. The standard is satisfied when the calculated Voz meets both the per-person and per-area minimums.

Does ventilation really cost that much in energy?

Outdoor air must be heated or cooled to room temperature, which is a significant energy load. In cold climates, unconditioned OA can represent 20–40% of HVAC energy. HRV (Heat Recovery Ventilator) and ERV (Energy Recovery Ventilator) units recover 60–80% of that energy, dramatically reducing the cost while meeting code.

Can I use this for a building permit?

This calculator uses published ASHRAE 62.1 and 62.2 formulas and is accurate for preliminary design and education. Building permits typically require stamped mechanical engineering drawings. Use these results for pre-design sizing and contractor discussions; a licensed engineer should review the final design.

What does Ez = 0.8 vs 1.0 mean in practice?

Ez = 1.0 applies to most standard ceiling-supply ceiling-return systems. Ez = 0.8 applies when return air is taken from a low sidewall or when supply air temperature is significantly below room temperature in heating mode. A lower Ez means less effective mixing, so more outdoor air is required to meet the breathing zone target.

Ventilation Rate Calculator

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