Choose between a silent and an open frame set on three numbers, not on appearance: the sound level your site is allowed in dB(A), the length and width you have in metres, and the weight the access route can carry. A sound-attenuated canopy on the same generator typically removes 20 to 25 dB(A), adds around 1.5 to 2 m of length and takes the transport weight up by 10 to 20 %. In exchange it also restricts airflow, so the set has to be checked for a higher temperature inside the enclosure.
What the canopy actually changes
| Property | Open frame | Silent canopy |
|---|---|---|
| Sound pressure at 1 m | About 95 to 105 dB(A) | About 75 to 85 dB(A) |
| Length | Bare set length | Adds about 1.5 to 2 m |
| Transport weight | Bare set weight | Adds about 10 to 20 % |
| Fuel tank | Separate day tank or base tank on request | Usually an integral base tank under the set |
| Service access | All sides open | Side and end doors, with clearance for them to open |
| Cooling | Ambient air straight to the radiator | Radiator and air path sized for the enclosure; the set may be de-rated for it |
| Weather protection | Requires a plant room or a roof | Outdoor rated as supplied |
Distance is half of the sound figure
Sound pressure falls by about 6 dB(A) every time the distance doubles. So a set declared at 85 dB(A) at 1 m is roughly 68 dB(A) at 7 m, and two datasheets can look 20 dB apart simply because one was measured at 1 m and the other at 7 m. Before comparing anything, put both figures at the same distance:
| Distance from the set | Change from 1 m | If the figure at 1 m is 100 dB(A) |
|---|---|---|
| 1 m | reference | 100 dB(A) |
| 2 m | about -6 dB(A) | 94 dB(A) |
| 4 m | about -12 dB(A) | 88 dB(A) |
| 7 m | about -17 dB(A) | 83 dB(A) |
| 14 m | about -23 dB(A) | 77 dB(A) |
The 6 dB per doubling rule assumes a free field – no walls, no reflections. A plant room, a courtyard between buildings or a roof terrace will be louder than this calculation suggests, and a reflective wall behind the set can add 3 dB(A) or more on its own.
When an open frame set is the right answer
- The set lives in a plant room or a purpose-built enclosure with its own acoustic treatment.
- The site has no neighbours and no night-time limit – a remote camp, a quarry, a laydown yard.
- Service access matters more than sound: an open set is quicker to inspect and easier to work on.
- The set is only used in an emergency and the noise lasts as long as the outage.
When the canopy is not optional
- Hospitals and clinics, where a set can run at night next to occupied wards. See diesel generators for hospitals.
- Hotels and residential towers, where the set is often within 20 m of a guest room. See diesel generators for hotels.
- Data centres in cities, where the set must pass a commissioning test at night at full load. See diesel generators for data centers.
- Any site with a written noise limit at the property boundary. Ask for the figure in dB(A) and the distance it is measured at before you accept a model.
Conditions that change the answer
- Airflow. A canopy is a closed box around a hot engine. The enclosure has to be sized for the airflow, and the set is often rated lower inside a canopy than in the open – the datasheet figure applies to the set as supplied, so compare like with like.
- Ambient. A canopy at 50 C site temperature is a harder duty than the same canopy at 25 C. Both the rating and the sound figure are declared at stated conditions.
- Access. Doors need clearance to open fully. A canopy that fits the concrete plinth but cannot open its doors is a service problem on day one.
- Retrofit. Adding a canopy later means re-checking the cooling, and it may mean de-rating the set or enlarging the radiator. Decide the enclosure before the quotation.
- Duty. A prime-rated set runs for thousands of hours; the enclosure has to be right for that duty, not just for the noise test. See prime vs standby power.
Questions
How many dB(A) does a sound-attenuated canopy remove?
Typically 20 to 25 dB(A) at the same measurement distance: an open set declared at about 100 dB(A) at 1 m is commonly quoted at 75 to 85 dB(A) at 1 m in a standard canopy. Higher tiers of attenuation exist for hospitals and city-centre data centres, and they are usually supplied as a containerised acoustic package rather than a bolt-on canopy.
Can I add a canopy to a set I already own?
It is possible, but it is a cooling decision as much as a metalwork one. The enclosure raises the air temperature around the radiator, so the set may have to be de-rated, or the radiator and fan changed. Budget for the re-rating test as well as the canopy. Choosing the enclosure at the quotation stage is always cheaper than retrofitting it.
What is the quietest set for a 400 kVA requirement?
For that band, a containerised set with an acoustic package is usually the quietest practical option, because the container gives room for larger attenuators and a longer air path than a canopy bolted to the base frame. Ask for the sound pressure level in dB(A) at 7 m for the exact model, not for the family – the figure moves with the engine, the fan and the enclosure tier.
Does a silent set consume more fuel?
Not because of the canopy itself, but because of the airflow it restricts and because of how the set is loaded. A canopied set running at a higher internal temperature and a lower load can consume 20 to 30 % more fuel per kWh than the same set working at three-quarter load in the open. Right-sizing the set for the load matters more to the fuel bill than the enclosure type.
Compare the four options before you choose
The enclosure is one of four form factors, and each one has a page with its own trade-offs: silent diesel generators, containerised diesel generators, trailer mounted diesel generators and open frame diesel generators. If the rating is not settled yet, start with how to size a diesel generator and then bring the answer back to the form factor.
Give us the noise limit and the access route
The permitted dB(A), the distance it is measured at, and the widest point on the route to the plinth are enough for us to propose the enclosure.
Written and maintained by the KVA Grid sales engineering desk. Sound levels are typical values for the 100 to 500 kVA band at the distances stated and are not a guarantee; the datasheet for the quoted build governs. Reviewed 26 September 2026.