The calculator answers one question: how much air does this room need to move? It builds the answer from two parts — combustion air and heat‑rejection air — then adds them to size the inlet and outlet openings.
A diesel engine breathes air to burn fuel. This is small but non‑negotiable: roughly 6–7 m³/h per kilowatt (about 0.10 m³/min per kW), or 7 m³/kWh under the Chinese GB standard.
The engine and alternator shed heat into the room. The calculator estimates the airflow needed using the standard heat‑load formula: V = Q ÷ (Cp × ρ × ΔT).
The tool runs both parts, adds them, and converts the total into m³/h, m³/s, and CFM. Then it sizes the inlet and outlet openings from a standard face velocity of about 5 m/s.
The calculation uses the standard heat-load formula: V = Q ÷ (Cp × ρ × ΔT), where Q is the heat released into the room (kW), Cp is the specific heat of air (1,005 J/kg·K), ρ is air density (1.2 kg/m³), and ΔT is the room temperature rise you allow (typically 10 K). The total ventilation — combustion air plus heat‑rejection air — determines the louver area needed at a standard face velocity of about 5 m/s.
The air the engine needs to burn fuel — roughly 6–7 m³/h per kW, non‑negotiable for safe operation.
The airflow needed to carry away engine and alternator heat without exceeding your allowed room temperature rise.
Combustion air plus heat‑rejection air — expressed in m³/h, m³/s, and CFM for easy equipment specification.
The inlet and outlet openings sized from a standard face velocity of about 5 m/s — the area you actually need to build.
Choose Quick Mode for a fast estimate based on generator power, or Advanced Mode for detailed calculations with altitude correction and multiple units. Both methods return total ventilation, combustion air, heat‑rejection air, and louver area.
Enter your generator's rated power and the allowed room temperature rise. The calculator returns the total airflow in m³/h, m³/s, and CFM.
Enter generator power, temperature rise, altitude, and number of units. Includes combustion air and louver area sizing from face velocity.
A generator room must serve two different air streams, and confusing them is the most common ventilation mistake. Combustion air is the air the engine draws into its cylinders — about 5–7 m³/h per kW. Cooling air removes heat from the radiator and alternator — far larger at 30–50 m³/h per kW.
| Component | Typical Airflow | Purpose |
|---|---|---|
| Combustion air | 5–7 m³/h per kW | Engine intake |
| Room heat removal | 15–25 m³/h per kW | Radiated heat from engine + alternator |
| Cooling (radiator) air | 30–50 m³/h per kW | Radiator heat rejection (ducted out) |
| Total ventilation | 50–80 m³/h per kW | All streams combined |
A diesel generator room needs a total ventilation rate of roughly 50–80 m³/h per kW (about 29–47 CFM per kW) to stay within a 10 °C maximum room temperature rise. In imperial terms, that is approximately 175–185 CFM per kW of heat rejected.
Ducted radiator discharge cuts the room's burden dramatically; un-ducted discharge forces the room to handle the full heat load. The calculator's advanced mode asks which applies.
Allow a 5 °C rise and you move more air; allow 15 °C and you move less — but the room gets hotter. The calculator lets you adjust ΔT to find the balance.
Both reduce air density and derate heat rejection. At altitude, the engine produces less power and the radiator rejects less heat — the calculator applies density correction.
Two generators in one plant room do not simply double — they interact. The calculator's multi-unit mode sizes them together, accounting for shared heat load and air distribution.
For a precise number, use V = Q ÷ (Cp × ρ × ΔT) rather than the rule of thumb. We publish actual heat-rejection data for our Cummins, Perkins, Weichai, and Yuchai engine options, so your calculation matches the unit you are actually buying.
Heat load: 300 kW (k = 0.3) · Allowed rise: 12 K. Airflow: 300,000 ÷ (1005 × 1.2 × 12) = 20.7 m³/s. That is ≈ 74,500 m³/h, or ≈ 43,900 CFM. Combustion air adds roughly 6,000 m³/h on top.
Airflow is only useful if you can get it into and out of the room. The formula is simple: free opening area = airflow ÷ face velocity. Use a standard face velocity of about 5 m/s (1,000 ft/min).
Formula: Free opening area = airflow ÷ face velocity. Using 5 m/s, a 1000 kW generator (20.7 m³/s) needs 4.15 m² of free opening area — roughly 45 ft².
Inlet area should be at least 1.5× the radiator face area (2× in hot climates). Outlet area should be at least 1.25× the radiator face area. Position the inlet low and the outlet high, on opposite walls.
A louver's gross area is larger than its free area. A louver rated at 80% free area needs 4.15 ÷ 0.8 = 5.2 m² of physical louver to deliver 4.15 m² of effective opening.
Louver separation: minimum 3 m between inlet and outlet. Clearances: 1.0 m on all sides of the generator, 1.5 m on the radiator discharge side. Room height: minimum 3.5 m.
Maximum room temperature rise: 10 °C above ambient. Air-cooled rooms should not exceed 35 °C. Combustion air intake temperature: no higher than 40 °C.
Room height: minimum 3.5 m, with 4.0 m preferred above 500 kW. The calculator reports free opening area so you can apply your louver's free-area ratio and position openings correctly.
The governing standards vary by market, and a global supplier should design to all of them. We design to the standard your project cites. For an export order, that often means confirming compliance against more than one.
Combustion air and heat-removal ventilation for emergency and standby power systems. Defines runtime classes, fuel storage requirements, and ventilation criteria for critical facilities and Level 1 systems.
Reference conditions, rating definitions, and performance testing for generator sets. The basis for derating, heat-rejection calculations, and nameplate ratings across all markets and applications.
Mechanical ventilation air-change rates for buildings. Specifies minimum ventilation requirements for generator rooms, occupied spaces, and compliance with local building codes.
Combustion air at 7 m³/kWh. CO limited to 30 mg/m³ and acrolein to 0.3 mg/m³ in occupied spaces. The standard your project cites determines the design basis.
For an export order, compliance often means confirming against more than one standard. We design to the standard your project cites and publish actual heat-rejection data for our engine options — Cummins, Perkins, Weichai, and Yuchai.
Final ventilation design should be checked against the complete load schedule, engine heat-rejection data, site conditions, and applicable codes (NFPA 110, ISO 8528-5, AS 1668.2, GB standards) before construction begins. We publish actual heat-rejection data for our engine options so your calculation matches the unit you are actually buying.
Ventilation is not a bolt-on afterthought; it is part of the generator’s performance envelope. A correctly sized room keeps the engine within its rated temperature range and keeps standby power reliable for its full service life.
A: Estimate the heat released into the room with Q = k × P (k ≈ 0.3), convert it to airflow with V = Q ÷ (1005 × 1.2 × ΔT), then add combustion air of about 6–7 m³/h per kW. Total ventilation typically lands near 50–80 m³/h per kW.
A: A diesel generator room needs roughly 50–80 m³/h per kW of rated power to stay within a 10 °C maximum room temperature rise — about 29–47 CFM per kW in imperial units.
A: A diesel engine needs about 5–7 m³/h per kW for combustion — roughly 0.10 m³/min per kW, or 7 m³/kWh under the Chinese GB standard. This is small compared to the cooling air but is a fixed requirement.
A: Radiator cooling air is typically 30–50 m³/h per kW. In a well-designed room this hot air is ducted directly outside, so the room itself only handles combustion air plus radiated heat.
A: Divide total airflow by a face velocity of about 5 m/s to get free opening area. Size the inlet at 1.5× radiator face area and the outlet at 1.25×, then divide by the louver’s free-area ratio for gross area.
A: Design for a maximum 10 °C rise above ambient. Air-cooled rooms should stay at or below 35 °C, and combustion air intake should not exceed 40 °C.
A: It depends on the heat load and layout. Large or basement installations usually need mechanical fans; small ground-level rooms can sometimes use natural draft. Use the calculator to estimate airflow, then our engineers confirm the fan requirement.
A: Allow at least 1.0 m on all sides and 1.5 m on the radiator discharge side, with a minimum room height of 3.5 m (4.0 m above 500 kW).
