Generator Room Ventilation Calculator
Combustion and cooling air for a standby generator room.
Enter your values
Enter the generator rating in kW.
Enter the radiator fan airflow in CFM.
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.
- Combustion air needed
- 375 CFM
- Radiator cooling airflow
- 12,000 CFM
- Design room airflow (larger of the two)
- 12,000 CFM
- Inlet louvre area at 500 FPM
- 24 sq ft
Quick answer
Generator rooms need combustion air (about 2.5 CFM per kW plus radiator airflow), typically dominated by the radiator's own airflow requirement which can be several thousand CFM.
Combustion CFM = 2.5 x kW rating; total CFM often set by radiator fan flow
At a glance
| What it does | Combustion and cooling air for a standby generator room. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Generator rating, Radiator fan airflow |
| Main output | Combustion air needed |
| Formula | Combustion CFM = 2.5 x kW rating; total CFM often set by radiator fan flow |
| Cost | Free — no sign-up, no download |
How to use the Generator Room Ventilation Calculator
- 1Enter the generator's kW rating for combustion air estimate.
- 2Enter the radiator/cooling fan's rated airflow from the spec sheet.
- 3Size room inlet louvres for whichever airflow is larger — usually the radiator.
Inputs explained
- Generator rating(kW)
- Enter the generator rating in kW.
- Radiator fan airflow(CFM)
- Enter the radiator fan airflow in CFM.
Worked example
Using the values the calculator loads with:
Inputs
- Generator rating150 kW
- Radiator fan airflow12000 CFM
Results
- Combustion air needed375 CFM
- Radiator cooling airflow12,000 CFM
- Design room airflow (larger of the two)12,000 CFM
- Inlet louvre area at 500 FPM24 sq ft
Frequently asked questions
Why does radiator airflow dominate?
Radiator-cooled gensets move far more air for engine cooling than they need for combustion alone.
What about exhaust heat?
The hot discharge air must have a clear, unobstructed path out, ideally opposite the intake to avoid recirculation.
What do I need to enter into the Generator Room Ventilation Calculator?
Just 2 values: generator rating, radiator fan airflow. 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 Generator Room Ventilation Calculator work out the answer?
Generator rooms need combustion air (about 2.5 CFM per kW plus radiator airflow), typically dominated by the radiator's own airflow requirement which can be several thousand CFM. It applies the formula Combustion CFM = 2.5 x kW rating; total CFM often set by radiator fan flow and shows the working so you can check each step by hand.
Is the Generator Room Ventilation 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.