In short. A stationary generator is a permanent part of the building or plant, so the installation becomes part of the generator. Foundation, room or enclosure, cooling airflow, exhaust, bulk fuel, switchgear, cabling and earthing are engineered around the machine once, and the facility lives with those decisions for twenty years. Get the architecture right before construction closes in: duty, autonomy, service access and future expansion all have to be settled while the walls are still on paper.
What permanence changes
A rental set arrives, runs and leaves. A stationary diesel generator set is positioned once, and everything around it is built to suit. That brings real advantages: a room or enclosure designed for the airflow the engine needs, bulk fuel sized for the required autonomy, a permanent exhaust route, fixed switchgear and automatic transfer, remote monitoring and, where needed, synchronising with other sets. It also raises the cost of error. A room 300 mm too short for the radiator to be pulled, a louvre facing the monsoon wind, or a switchboard that cannot accept a second set are mistakes that cannot be corrected cheaply once the slab is poured.
| Design input | Question to settle | What it drives |
|---|---|---|
| Site | Indoor room, rooftop or ground-level enclosure | Ventilation, exhaust route, acoustic treatment, crane access |
| Duty | Standby, prime or continuous under ISO 8528-1 | Engine rating, cooling margin, service regime |
| Load | Steady, motor-heavy, nonlinear or mixed | Alternator frame, controller, neutral sizing |
| Autonomy | Hours the facility must run without refuelling | Day tank and bulk tank size, PESO licensing |
| Service access | Can radiator, alternator and heads be reached and removed | Room dimensions, door sizes, lifting beam |
| Expansion | Will a second set, larger switchgear or more fuel be needed | Spare bay, bus rating, tank farm space |
Foundation and vibration
A generator set on anti-vibration mounts between the engine-alternator and its base frame needs a level, rigid plinth rather than a massive isolated block; the mounts do the isolating. The plinth is typically raised 150 to 300 mm above the floor to keep the set clear of water and make draining practical, extends beyond the base frame on all sides, and is designed by the structural engineer for the static weight plus the dynamic load in the manufacturer’s installation manual. Sets without integral mounts, and large sets on upper floors or rooftops, need the vibration isolation designed specifically, because vibration transmitted into a structure is felt several floors away. The manufacturer’s mounting drawing is the governing document and should be in the civil contractor’s hands before the plinth is cast.
The room as a heat-rejection system
A generator room is a heat-rejection system with a generator inside it. The radiator must draw cool air through an inlet louvre, push hot air out through an outlet louvre with a flexible duct connection, and the engine must draw its combustion air from the same room without starving it. The volume of air is large: a 500 kVA set may need in the order of 10 to 15 cubic metres per second of cooling air, and the inlet and outlet openings must be sized for that flow at the low pressure a pusher radiator fan can develop, including the resistance of louvres, bird screens and acoustic attenuators. Room temperature rise above ambient should be held within the engine’s limit, usually 10 to 15 degrees Celsius, because every degree of intake temperature above the rating condition takes capacity away, and Telangana summers already start at 42 degrees. The generator room ventilation guide gives the calculation, and the indoor installation page covers layout.
Cooling airflow (m³/s) = Heat radiated to room (kW) ÷ (1.2 × 1.005 × allowable temperature rise (°C))
Heat radiated to room is the engine and alternator radiation figure from the data sheet, excluding radiator heat, 1.2 is the density of air in kilograms per cubic metre and 1.005 its specific heat in kilojoules per kilogram per degree. For a set radiating 45 kW with a 12 degree allowable rise, the room ventilation air alone is about 3.1 cubic metres per second (illustrative), to which the radiator’s own airflow is added when it draws from the room.
Exhaust, fuel and switchgear
A permanent exhaust route runs from the engine through a flexible bellows, a silencer selected for the required attenuation, and insulated pipe to a termination that keeps fumes away from windows, air intakes and neighbours. The total backpressure at full load must stay within the engine’s limit, which caps the length and the number of bends; a long run to a roof often needs a larger pipe diameter than the engine outlet. The exhaust backpressure guide covers the check. Fuel for a stationary set is normally a day tank in or beside the base frame and a bulk tank outside the room, with a transfer pump, filtration and level monitoring; storage above the quantity exempted under the Petroleum Rules requires a PESO licence, and the bulk tank location is subject to fire separation. The electrical side includes the generator breaker, the AMF or synchronising panel, cables sized for current and voltage drop over the actual route, and earthing of the neutral and frame integrated with the building’s earthing system. The AMF panel page describes the transfer arrangement most stationary sets use.
Serviceability and expansion
A stationary set must be serviceable for the whole of its life, not only installable on day one, and the service and maintenance it will need should shape the room. Radiator cleaning needs access to the core face. Battery replacement needs a clear side. Injector and head work needs clearance above the engine and, for larger sets, a lifting beam. Alternator bearing replacement needs space to withdraw the rotor or at least the end bracket. A major overhaul may need the set lifted out, which means a door or removable panel larger than the set and a route to it. Where the facility is likely to grow, leave a second bay, specify the switchboard bus for two sets and consider synchronising-ready controllers from the start. Multiple stationary sets in one power house, operated in parallel with load sharing and automatic sequencing, turn a generator room into a small power plant, and the paralleling page covers what that adds.
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Common mistakes
- Sizing the room for the generator’s footprint rather than its airflow and service clearances. The set overheats on hot afternoons and the radiator cannot be removed without breaking a wall.
- Routing a long exhaust to the roof in the engine’s outlet diameter. Backpressure exceeds the limit, the turbocharger runs hot and output falls.
- Locating the bulk fuel tank without checking Petroleum Rules quantities and fire separation. The installation cannot be licensed and the tank has to be moved.
- Casting a massive isolated foundation block under a set that already has anti-vibration mounts. Money is spent on mass that does nothing, while the real need, a level rigid plinth with drainage, is missed.
- Specifying switchgear for one set with no spare bay. The second set the facility needs five years later requires a new switchboard.
What to send us
Send the load list or maximum demand, the required autonomy in hours, and the architectural drawings or a sketch of the proposed room or enclosure location with dimensions, door sizes and the route to the roof or outside for exhaust. Include the site address for ambient and noise context, the position of the main switchboard, and whether a second set or future expansion is likely. Send your stationary generator requirement.
Questions engineers ask
How big should a generator room be?
Large enough for the set plus at least one metre of clear space on the service sides and 1.5 metres at the radiator and alternator ends, with inlet and outlet louvre areas sized for the cooling airflow, and a door or removable panel through which the set can be brought in and taken out. The manufacturer’s installation drawing gives the minimum clearances.
Does a stationary generator need a special foundation?
Most sets with integral anti-vibration mounts need a level, rigid reinforced concrete plinth raised above floor level and designed for the set’s static and dynamic loads, not an isolated inertia block. Rooftop and upper-floor installations need vibration isolation designed for the structure.
How much diesel can be stored without a licence?
The Petroleum Rules exempt storage of a limited quantity of diesel, which is Class B petroleum; above that quantity a PESO licence is required and the tank must meet construction and separation requirements. Confirm the current threshold and the tank location with the licensing authority before the civil design is fixed.
Can a stationary set be installed on a rooftop?
Yes, provided the structure is designed for the load and vibration, there is a lifting route, exhaust and hot air discharge clear of occupied areas, fuel at height is limited to what the fire authority allows, and boundary noise meets CPCB limits. An acoustic enclosed set is the usual choice.
Generators by rating
- Under 15 kVA generators
- 15–50 kVA generators
- 50–125 kVA generators
- 125–250 kVA generators
- 250–500 kVA generators
- 500–1000 kVA generators
- 1–2 MVA generators
- 2 MVA and above generators
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.