ACH uses the current airflow rate from the converter above. Enter room dimensions or total volume, then enter or convert your airflow rate.
Conversion Factors
1 L/s = 2.1189 CFM = 3.6000 m³/h = 0.001000 m³/s
1 m³/h = 0.58858 CFM = 0.27778 L/s = 0.016667 CMM
1 m³/s = 2118.9 CFM = 1000 L/s = 3600 m³/h
ACH = m³/h / room volume (m³)
ASHRAE 62.1 Ventilation Rates -- Commercial Spaces
| Space Type | Per Person (L/s) | Per Person (CFM) | Per Area (L/s/m²) | Notes |
|---|---|---|---|---|
| Office (general) | 10 | 21 | 0.3 | ASHRAE 62.1-2022 |
| Conference room | 10 | 21 | 0.3 | Higher density |
| Classroom (K-12) | 5 | 10.6 | 0.6 | Higher area rate |
| Retail store | 15 | 31.8 | 0.9 | Variable occupancy |
| Restaurant (dining) | 10 | 21 | 0.9 | Higher pollutant load |
| Gym / fitness | 20 | 42.4 | 0.6 | Higher activity level |
| Hotel lobby | 10 | 21 | 0.3 | Variable occupancy |
| Healthcare patient room | 10 | 21 | 0.6 | Dilution of pollutants |
| Parking garage | -- | -- | 3.0 | CO / vehicle exhaust |
Typical ACH Ranges by Application
| Space Type | ACH Range | Notes |
|---|---|---|
| Residential bedroom | 0.35 - 1.0 | NBC minimum + comfort range |
| Residential living area | 0.35 - 2.0 | Natural + mechanical combined |
| Residential kitchen | 7.5 - 15 | During cooking (range hood) |
| Residential bathroom | 8 - 12 | Spot exhaust during use |
| Office space | 6 - 10 | ASHRAE 62.1 compliant design |
| Classroom | 4 - 8 | Higher for occupied periods |
| Hospital operating room | 20 - 25 | CSA Z317.2 minimum 20 ACH |
| Hospital patient room | 6 - 12 | Includes transfer air |
| Data centre | 30 - 60+ | Cooling dominated |
| Clean room (ISO 7) | 60 - 90 | ISO 14644-1 specification |
| Parking garage | 4 - 6 | CO control per NBC |
| Restaurant kitchen | 30 - 60 | Make-up air matches hood |
ASHRAE 62.2 Residential Ventilation (Whole-Home)
| Floor Area (m²) | 1-2 Bedrooms (L/s) | 3 Bedrooms (L/s) | 4 Bedrooms (L/s) | 5+ Bedrooms (L/s) |
|---|---|---|---|---|
| Up to 93 m² (1000 ft²) | 21 | 28 | 35 | 42 |
| 93 - 185 m² (1000-2000 ft²) | 28 | 35 | 42 | 49 |
| 185 - 279 m² (2000-3000 ft²) | 35 | 42 | 49 | 56 |
| 279 - 465 m² (3000-5000 ft²) | 42 | 49 | 56 | 63 |
| Over 465 m² (5000+ ft²) | 49 | 56 | 63 | 70 |
Based on ASHRAE 62.2-2022. Canadian homes must also comply with the National Building Code Section 9.32 and applicable provincial requirements. Use the HRV Ventilation Calculator for full residential design.
How to Use the Airflow Unit Converter
Enter a value in CFM, L/s, m³/h, m³/s, or CMM. All other units update instantly. Use the quick-reference presets for common HVAC values: residential furnace blowers, bathroom exhaust fans, kitchen hoods, and commercial AHUs.
Enter room length, width, and height in metres (or total volume directly). The ACH calculator divides your current airflow by the room volume and shows ACH, plus the number of minutes per complete air change. Enter ACH directly in the ACH field and it back-calculates flow rate using your room volume.
The result panel identifies what HVAC application your airflow value represents: bathroom exhaust, residential ventilation, residential air handler, commercial AHU, or large industrial system. This helps catch unit mix-ups before they affect equipment selection.
Three reference tables cover ASHRAE 62.1 commercial rates by space type, typical ACH ranges for 12 space categories, and ASHRAE 62.2 whole-home residential ventilation rates. Use these alongside the HRV Ventilation Calculator and Exhaust Fan Sizing Calculator for complete ventilation design.
Airflow Units in HVAC -- Complete Guide
Airflow measurement is central to HVAC design, commissioning, and troubleshooting. The right unit depends on the application and the region. Canadian HVAC work spans at least three active unit systems: CFM from US equipment, L/s from Canadian engineering standards, and m³/h from European equipment and international standards. The airflow targets behind these numbers come from ASHRAE Standards 62.1 and 62.2, the governing references for commercial and residential minimum ventilation. Fluency across all three unit systems prevents costly specification errors.
CFM to L/s -- The Core Canadian Conversion
The most common airflow conversion in Canadian HVAC is CFM to L/s. Equipment from US manufacturers -- furnaces, heat pumps, AHUs, fans -- carries CFM ratings. Canadian engineering specifications, HVAC drawings, and code compliance reports use L/s. The conversion factor is 1 CFM = 0.4719 L/s, or equivalently 1 L/s = 2.119 CFM. A 400 CFM furnace blower delivers 188.8 L/s. A 25 L/s kitchen exhaust fan moves 53 CFM. For just this conversion, the dedicated CFM to L/s Converter is faster.
m³/h and CMM for Commercial and European Equipment
European heat pumps, ventilation units, and chillers rate airflow in m³/h. The conversion from CFM: 1 CFM = 1.699 m³/h. A 2000 CFM AHU delivers 3398 m³/h. CMM (cubic metres per minute) appears less often but is used in some industrial and large commercial references: 1 CMM = 1000 L/min = 16.667 L/s = 35.31 CFM. Always check the unit on European equipment datasheets -- m³/h and m³/s look similar but differ by a factor of 3600.
Air Changes Per Hour (ACH)
ACH describes how many times per hour the total air volume of a space is replaced. It's calculated by dividing the volumetric flow rate (m³/h) by the room volume (m³). ACH is used in ventilation design, IAQ assessment, infection control, and code compliance checks. A hospital operating room requires a minimum of 20 ACH per CSA Z317.2, the Canadian standard governing HVAC systems in health care facilities. A residential bedroom needs at least 0.35 ACH per NBC requirements. The ACH calculator above handles this directly when you enter room dimensions.
Canadian Ventilation Standards
The National Building Code of Canada Section 9.32 and ASHRAE 62.2 govern residential ventilation. ASHRAE 62.1 governs commercial ventilation. The NBC requires continuous whole-home mechanical ventilation in new residential construction -- typically delivered by an HRV or ERV. Minimum flow rates depend on floor area and number of bedrooms. For a typical Canadian home of 150 m² with 3 bedrooms, the ASHRAE 62.2 minimum whole-home ventilation rate is approximately 35 L/s (74 CFM). Use the HRV Ventilation Calculator to size HRV systems to these requirements.
Airflow in Duct Design
Duct sizing uses airflow per zone along with velocity and static pressure constraints. Canadian duct design typically uses L/s per room or zone, converted from the total system CFM. A common target is 7-10 L/s per person for office spaces, or 10-15 L/s per bedroom for residential heating and cooling distribution. Feed converted airflow values into the Duct Sizing Calculator to size ductwork for velocity, pressure drop, and noise criteria.
Frequently Asked Questions
Multiply CFM by 0.4719 to get L/s. To go the other direction, multiply L/s by 2.119. A 400 CFM blower delivers 188.8 L/s; a 25 L/s bathroom fan moves 53 CFM. This is the single most common airflow unit conversion in Canadian HVAC. For just this pair, the dedicated CFM to L/s Converter is the quickest tool.
ACH = airflow rate in m³/h divided by room volume in m³. For example, a 50 m³ office supplied with 300 m³/h has 6 ACH. Convert CFM to m³/h by multiplying by 1.699 first. The ACH section of this converter handles all the math -- enter room dimensions and your airflow rate and it calculates ACH, plus minutes per complete air change.
ASHRAE 62.2-2022, adopted by the NBC, requires whole-home mechanical ventilation scaled to floor area and bedroom count. A 150 m² home with 3 bedrooms needs roughly 35 L/s (74 CFM) of continuous ventilation, per the reference table above. Bathroom exhaust fans must provide at least 10 L/s (21 CFM) during use. Kitchen exhaust must provide at least 25 L/s (53 CFM) during cooking. Provincial codes may have additional requirements, so always check your jurisdiction. Use the HRV Ventilation Calculator for a complete residential design.
All three measure the same thing -- volumetric flow rate of air -- just in different unit systems. CFM (cubic feet per minute) is standard on North American equipment. L/s (litres per second) is the Canadian engineering standard. m³/h (cubic metres per hour) is common in European equipment. The conversions: 1 CFM = 0.4719 L/s = 1.699 m³/h. A specification error between these units causes equipment undersizing or oversizing by a factor of 2 to 3600 depending on which pair is confused.