Marine Engine Room Ventilation Calculator
Sizing marine engine room ventilation for a new build, a repower or a retrofit, on a vessel or a drilling rig? We handle all of them & much more. We match supply fans, louvers, sound attenuation and explosion-proof fans to your airflow, engine count and classified spaces.
The calculator below gives an ISO 8861 estimate. We size it, quote it, and return a submittal-ready selection.
Our offices are in Houston and Dallas-Fort Worth, serving Texas and the Gulf Coast, and we ship nationwide.
Have questions? Need a quote?
Calculate Engine Room CFM, Fan Size and Louver Free Area
Enter the engine power and the number of engines. The calculator returns the ISO 8861 design airflow in CFM, the airflow per fan and the louver free area for vessels and drilling rigs.
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Engines
HPEngine type -
Heat
BTU/min°F -
Total airflow
ISO 8861 takes the larger of two checks: combustion air plus heat-removal air, or 1.5 times the combustion air.
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Fans
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Louvers
fpmfpmIntake default sits under the AMCA-certified point where rain starts to pass a drainable louver (912 to 1,250 fpm on the Pottorff louvers checked). Discharge default is the 6 m/s (1,180 fpm) limit in German flag-state form DE.2. Louver size assumes 50% free area. Drainable louvers checked run 50 to 61%.
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Classified space
Does this engine room border a fuel, pump or other classified space?
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Engine Room Ventilation Questions
How much combustion air does a marine diesel engine need?
A 4-stroke marine diesel engine needs about 2.8 CFM of combustion air per horsepower at full load, based on the ISO 8861 guidance value of 0.0020 kg per kW per second at 95°F. A 2-stroke engine needs about 3.2 CFM per horsepower. Use the figure on the engine data sheet when you have one.
Does a drilling rig engine room use the same calculation as a ship?
A drilling rig engine room uses the same calculation as a ship. ISO 15138:2007, the offshore HVAC standard, sends engine room ventilation back to ISO 8861. The one addition for rigs is that emergency generator and fire pump rooms must also remove the heat left in the engine right after it shuts down.
What heat rejection should I use without an engine data sheet?
Without a data sheet, use the ISO 8861 heat loss curve, which gives heat to the room as a share of engine power. A 1,000 kW 4-stroke engine gives off about 5.3%, and the share falls to about 2.5% above 10,000 kW. The calculator applies this curve when the field is left blank.
Is the calculated airflow a set point for the fans?
The calculated airflow is a maximum, not a set point. ISO 8861 sizes the room for every engine at full rating on a 95°F day, with standby generators left out. When fewer engines run, fans on a variable speed drive or a thermostat can run slower and still hold the room under the 22.5°F rise.
How the ISO 8861 Engine Room Calculation Works
ISO 8861:1998 sizes engine room ventilation as the larger of two checks: combustion air plus heat-removal air, or 1.5 times the combustion air. The standard assumes 95°F outside air and a maximum rise of 22.5°F (12.5 K) across the room.
Drilling rigs use the same method, because ISO 15138 refers engine rooms back to ISO 8861.
| Step | Formula | ISO 8861 value |
|---|---|---|
| Combustion air | Engine kW × 0.0020 ÷ 1.13 | 0.0023 for 2-stroke engines (clause 5.2) |
| Heat to the room | Engine kW × heat loss % | Data sheet, or the Figure 1 curve (clause 6.1) |
| Heat-removal air | Heat kW ÷ (1.13 × 1.01 × 12.5), minus 0.4 × combustion air | Clause 5.3 |
| Design airflow | Larger of the two checks | Clause 5.1 |
The formulas give m³/s. One m³/s equals 2,119 CFM.
Worked example: two 1,000 HP 4-stroke engines total 1,491 kW. Combustion air is 5,593 CFM. At 5.9% heat loss, 88 kW reaches the room, which needs 10,866 CFM to remove. The design airflow is 16,459 CFM, well above the 8,390 CFM floor. Two running supply fans at 8,230 CFM each, plus one standby, cover it.
The result is a maximum with every engine at full rating. We leave out exhaust piping because it is insulated and handled separately. Boilers are not included.
Sizing Louvers for Engine Room Intake and Exhaust
Engine room louver size comes from free area: the design airflow divided by the air speed the louver can pass before rain gets through.
For 16,459 CFM at 900 fpm, the intake needs 18.3 ft² of free area, about 36.6 ft² of louver face at 50% free area. Discharge louvers can run faster, up to 1,180 fpm (6 m/s), before an exhaust fan is needed.
Marine louvers for engine room ventilation
We supply marine louvers for intakes and discharges, droplet separators where salt spray reaches the intake, and acoustic louvers where the engine room sits near crew spaces.
We size the louver to its opening for low pressure drop and quote it with the fans.
Engine Rooms Next to Fuel or Pump Rooms
An engine room that borders a fuel, pump or other classified space can need explosion-proof fans, because any fan that serves or draws air through the hazardous area must not become an ignition source.
AMCA Standard 99-0401 grades spark-resistant fan construction as Type A, B or C. Marine and offshore buyers usually specify the motor to ATEX or IECEx.
We check the area classification against the fan, motor and damper before we quote, and supply explosion-proof fans built for marine duty.
Related Products
- Marine industry HVAC – Ventilation and heating for vessels, shipyards and offshore units
- Offshore HVAC systems – Platform and rig HVAC built to ISO 15138
- Generator room ventilation – Airflow and louvers for onshore generator rooms
- A-60 marine fire dampers – Fire-rated dampers for engine room bulkhead penetrations
- Marine shut-off dampers – Closures for engine room supply and exhaust openings
- Marine non-return dampers – Stop backflow through idle fans
- Marine duct heaters – Electric heat for marine air handling
- Makeup air units for cruise ships – Conditioned outside air for large vessels