ERV / HRV Sizing Calculator
Balanced ventilation airflow for a home.
Enter your values
Enter the floor area in sq ft.
Enter the bedrooms you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Continuous ventilation
- 90 CFM
- Unit size to specify
- 90 CFM
- In L/s
- 42
- Occupants assumed
- 4
- Intermittent equivalent (50% duty)
- 180 CFM
Quick answer
Balanced ventilation is sized at roughly 0.03 CFM per square foot plus 7.5 CFM per occupant.
CFM = 0.03 x sq ft + 7.5 x (bedrooms + 1)
At a glance
| What it does | Balanced ventilation airflow for a home. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Floor area, Bedrooms |
| Main output | Continuous ventilation |
| Formula | CFM = 0.03 x sq ft + 7.5 x (bedrooms + 1) |
| Cost | Free — no sign-up, no download |
How to use the ERV / HRV Sizing Calculator
- 1Enter conditioned floor area and bedroom count.
- 2Choose a unit rated at or just above the result at 0.4 in wc.
- 3Balance supply and exhaust within 10% at commissioning.
Inputs explained
- Floor area(sq ft)
- Enter the floor area in sq ft.
- Bedrooms
- Enter the bedrooms you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Floor area2000 sq ft
- Bedrooms3
Results
- Continuous ventilation90 CFM
- Unit size to specify90 CFM
- In L/s42
- Occupants assumed4
- Intermittent equivalent (50% duty)180 CFM
Frequently asked questions
ERV or HRV?
ERV transfers moisture as well as heat — better in humid summers or very dry winters.
Can it replace bath fans?
A multi-port ERV can, if each wet room gets a dedicated exhaust pickup.
What do I need to enter into the ERV / HRV Sizing Calculator?
Just 2 values: floor area, bedrooms. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the ERV / HRV Sizing Calculator work out the answer?
Balanced ventilation is sized at roughly 0.03 CFM per square foot plus 7.5 CFM per occupant. It applies the formula CFM = 0.03 x sq ft + 7.5 x (bedrooms + 1) and shows the working so you can check each step by hand.
Is the ERV / HRV Sizing Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.