- October 11, 2026
- Posted by: Aceget
- Category: RECD & Emission Control Devices
“Guaranteed 70% particulate reduction.” “Backpressure within OEM limits.” Lines like these appear in almost every RECD offer. They sound reassuring, but on their own they guarantee very little. A performance figure without defined operating conditions is like a mileage claim without saying whether the car was tested on a highway or in city traffic. When the device underperforms, the vendor can point to your load, your fuel, your ambient temperature or your engine and argue that the guarantee never applied.
The fix is not to demand bigger numbers. It is to pin down the conditions under which the numbers must hold. This article lists the operating conditions that should be written into any RECD performance guarantee, explains why each one matters, and shows you how to turn them into a guarantee data sheet that both you and your vendor can sign with confidence.
First, What Exactly Is Being Guaranteed?
Before defining conditions, separate the different performance promises an RECD offer may contain. They are often blended into one sentence, but each needs its own definition.
| Guaranteed parameter | What it means | Why it matters to you |
|---|---|---|
| Particulate capture efficiency | Share of particulate matter removed from the exhaust | Core compliance requirement; regulators in many regions refer to a minimum of 70% PM capture for in-use DG sets |
| Clean backpressure | Pressure drop across a new or freshly cleaned RECD at a defined flow | Determines the margin left for your existing exhaust system |
| Maximum operating backpressure | Highest pressure drop before cleaning or regeneration is required | Protects the engine from overheating and power loss |
| Cleaning or regeneration interval | Running hours between maintenance events under stated conditions | Drives your maintenance cost and downtime |
| Effect on other emissions | Confirmation that CO, HC or NOx are not adversely affected | Avoids solving one problem while creating another |
| Noise contribution | Whether the RECD changes noise at stated points | Matters near residences, schools and hospitals |
| Design life of filter element | Expected life before replacement under stated duty | Key input for lifecycle cost |
The particulate capture figure is usually backed by certification testing under the CPCB framework, carried out by recognised agencies such as ICAT and ARAI. Directions from the Commission for Air Quality Management for the NCR have referred to a minimum 70% PM capturing efficiency for in-use DG sets up to 800 kW. But certification tells you how the device performed on a test engine under a test cycle. Your guarantee needs to tell you how it will perform on your engine under your conditions. That is where the conditions below come in.
If you need a refresher on how the device works, read what an RECD is and how it works and exhaust after-treatment systems explained simply.
The Twelve Operating Conditions to Define
Each condition below follows the same pattern: why it matters, how to define it in writing, and what to ask your vendor. You do not need extreme precision on every point, but you need enough that neither party can later claim the guarantee was based on a different engine or a different site.
Condition 1: Engine Identity and Rating
Why it matters: RECD sizing and certification depend on engine power range. Two DG sets with the same kVA can have engines with different displacement, aspiration and exhaust flow. Our article on why same-kVA DG sets may need different RECDs explains this in depth.
How to define it: Engine make, model, serial number, gross power in kW, rated speed, kVA rating, aspiration (naturally aspirated or turbocharged), governing (mechanical or electronic) and the emission stage the engine was originally certified to.
Ask the vendor: “Is this engine within the power range covered by the certification of the model you are offering?” See engine displacement and RECD selection, turbocharged versus naturally aspirated engines and mechanically governed versus electronic engines.
Condition 2: Exhaust Gas Flow and Temperature
Why it matters: Backpressure rises with flow, and many RECD designs need a minimum exhaust temperature for passive regeneration. A guarantee written without flow and temperature figures is a guarantee written for an imaginary engine.
How to define it: Exhaust gas flow and temperature at rated load and at your typical operating load, ideally from the engine OEM’s data sheet. Where OEM data is not available, state the method used to estimate it.
Ask the vendor: “Which flow and temperature values did you use to size the unit, and where did they come from?” Our guide on using OEM exhaust flow data to specify an RECD covers this, and specifying an RECD when original documents are missing handles the harder case.
Condition 3: Load Profile
Why it matters: Load drives exhaust temperature and soot production. A set that runs at 25 percent load produces cooler exhaust and often more soot per unit of fuel, which can load a filter faster than a set running at 70 percent.
How to define it: Minimum, typical and maximum load as a percentage of rating, and the approximate share of running time at each. Attach DG logbook extracts if available.
Ask the vendor: “Below what load does your guarantee on cleaning interval stop applying?” Useful references: using DG load logs to assess RECD suitability, choosing an RECD for low-load running and generator load factor and duty cycle.
Condition 4: Duty Type and Start-Stop Pattern
Why it matters: A standby set started weekly for a 15-minute test behaves very differently from a prime power set running ten hours a day. Frequent cold starts and short runs mean the exhaust may rarely get hot enough to support regeneration.
How to define it: Standby, prime or continuous duty; average number of starts per week; typical run duration; annual running hours.
Ask the vendor: “What is the minimum run duration at what load needed to maintain performance?” See RECDs for frequent short start-stop cycles, whether an RECD can work reliably during cold starts and prime power versus standby specifications.
Condition 5: Engine Condition Limits
Why it matters: Oil carryover, worn injectors and poor combustion overload a filter with soot and ash that it was never designed to handle. Vendors legitimately need protection from worn engines; you need protection from that being used as a blanket excuse.
How to define it: Agreed limits for lubricating oil consumption, visible smoke or opacity, and crankcase blow-by, recorded at installation as a baseline.
Ask the vendor: “Which engine parameters, at what values, would take my set outside your guarantee?” Read engine oil consumption and RECD suitability, and if smoke is already visible, why your generator emits black smoke and blue smoke.
Condition 6: Fuel Specification
Why it matters: Sulphur content, contamination and biodiesel blends affect catalyst activity, ash build-up and regeneration behaviour. Dual-fuel conversion changes the exhaust again.
How to define it: The fuel standard you use (for example, BS VI diesel), any blend percentage, and whether the set has been or may be converted to dual fuel.
Ask the vendor: “Does your guarantee hold if we use a biodiesel blend or convert to dual fuel later?” See how ultra-low sulphur diesel helps emission control, biodiesel blends on RECD-equipped generators and RECDs after dual-fuel conversion.
Condition 7: Ambient Temperature and Altitude
Why it matters: High ambient temperatures in DG rooms reduce cooling margins and raise surface temperatures around the RECD. High altitude changes air density, combustion and exhaust flow.
How to define it: Maximum and minimum ambient temperature at the installation point (not just the city average), and site altitude above sea level.
Ask the vendor: “Is any derating or design change needed for our site conditions?” Read assessing RECDs in very hot ambient conditions and RECD selection at high altitude.
Condition 8: Atmospheric Contaminants
Why it matters: Salt-laden air corrodes housings and fasteners. Industrial dust, lint and chemical fumes can enter the engine and affect exhaust composition, or settle on external components.
How to define it: Distance from the sea, presence of dust, fibres or corrosive vapours, and whether the DG room is enclosed or open.
Ask the vendor: “Which materials and coatings are you offering for these conditions?” See guides for coastal environments, dusty industrial locations, textile mills with lint exposure and water treatment plants with humidity and corrosion.
Condition 9: Exhaust System Configuration
Why it matters: The engine sees total backpressure from the whole exhaust system, not just the RECD. If your existing pipework already uses most of the OEM’s allowance, even a well-designed RECD can push the total over the limit.
How to define it: Pipe diameter, total length, number and type of bends, silencer type and location, rain cap or stack details, and existing measured backpressure without the RECD.
Ask the vendor: “Does your backpressure guarantee cover the RECD alone, or the total system after installation?” Background: how exhaust backpressure affects a DG set, positioning an RECD on a long exhaust run and RECD fitment on sets with multiple exhaust outlets.
Condition 10: Installation Location and Orientation
Why it matters: Installation inside a canopy, in a basement, on a rooftop or in a vertical orientation affects heat dissipation, drainage, access for cleaning and sometimes performance.
How to define it: Location, mounting orientation, enclosure details and available service clearance.
Ask the vendor: “Is the guaranteed performance valid in the orientation and location shown on the approved drawing?” See horizontal versus vertical mounting, fitting an RECD inside an acoustic canopy and service clearance around an RECD.
Condition 11: Maintenance Regime
Why it matters: Every performance guarantee assumes the device and engine are maintained. If that assumption is not written down, it becomes an argument.
How to define it: The cleaning or regeneration schedule, backpressure monitoring frequency, engine service intervals and who performs each task.
Ask the vendor: “Which maintenance tasks, if missed, would void the performance guarantee?” Our RECD maintenance guide and monthly DG maintenance checklist provide a baseline.
Condition 12: Future Changes
Why it matters: Facilities grow. A set running at 40 percent today may run at 75 percent after a new production line is added. That changes exhaust flow and backpressure.
How to define it: Expected load growth, planned fuel changes and any planned engine overhaul.
Ask the vendor: “Does the offered size leave headroom for our planned load increase?” Read specifying an RECD for future load increases.
Worked Example: Same DG Set, Two Very Different Guarantees
Imagine two 250 kVA DG sets with the same engine model. One serves a residential society; the other serves a small injection-moulding unit. On paper, both need the same RECD. In practice, their guarantee data sheets look quite different.
| Condition | Housing society set | Factory set |
|---|---|---|
| Duty | Standby; weekly test runs plus occasional outages | Prime; runs most of the day during frequent grid cuts |
| Typical load | 20–35% (lifts, pumps, common lighting) | 55–75%, with sharp swings as machines cycle |
| Annual hours | Low | High |
| Start pattern | Many short runs, often cold | Fewer, longer runs |
| Installation | Basement DG room with limited ventilation | Open yard beside the production shed |
| Main guarantee risk | Soot build-up and short cleaning intervals at low exhaust temperature | Backpressure at high flow and element life under heavy hours |
For the housing society, the guarantee conversation centres on cleaning interval at low load and the minimum run duration needed during weekly tests. The vendor might reasonably recommend running the set at a higher load during test runs, perhaps with a load bank, and that recommendation should be written into the maintenance regime. Our purchase planning guide for RWAs covers the committee side of this decision.
For the factory, the conversation centres on total backpressure at peak flow and the expected element life at high annual hours. Rapid load swings also matter, as covered in our guide on RECDs for plastic manufacturing units with cyclic machine loads.
If both buyers had accepted a generic “70% reduction, backpressure within limits” guarantee, neither would have been protected against the risk that actually matters on their site. That is the whole case for defining operating conditions.
How the Conditions Connect to Each Guarantee
Not every condition affects every guaranteed parameter equally. This matrix shows where to focus when you write the guarantee.
| Condition | PM capture | Backpressure | Cleaning interval | Element life |
|---|---|---|---|---|
| Engine identity and rating | High | High | Medium | Medium |
| Exhaust flow and temperature | Medium | High | High | Medium |
| Load profile | Medium | Medium | High | High |
| Start-stop pattern | Low | Medium | High | Medium |
| Engine condition | Medium | High | High | High |
| Fuel specification | Medium | Medium | High | High |
| Ambient and altitude | Low | Medium | Medium | Low |
| Atmospheric contaminants | Low | Low | Low | Medium (housing) |
| Exhaust configuration | Low | High | Low | Low |
| Installation location | Low | Low | Medium | Medium |
| Maintenance regime | Medium | High | High | High |
| Future changes | Medium | High | Medium | Medium |
Building a Guarantee Data Sheet
The cleanest way to capture all of this is a one- or two-page Guarantee Data Sheet attached to the purchase order. It has two halves: the conditions you declare, and the values the vendor guarantees under those conditions.
Part A: Buyer-Declared Operating Conditions
- Engine make, model, serial number, gross kW, rated speed, aspiration, governing
- Original emission stage of the engine
- Exhaust flow and temperature at rated and typical load, with source
- Load profile: minimum, typical, maximum and time share
- Duty type, starts per week, typical run duration, annual hours
- Baseline engine condition: oil consumption estimate, smoke observation, running hours since overhaul
- Fuel type and any blend
- Ambient temperature range at installation point, altitude
- Atmospheric contaminants and enclosure type
- Exhaust configuration and existing backpressure
- Planned changes in the next three to five years
Part B: Vendor-Guaranteed Values
- RECD model and certification reference
- Particulate capture efficiency as certified, with test reference
- Clean pressure drop across the RECD at stated flow
- Maximum total system backpressure after installation at rated load
- Backpressure alarm or cleaning setpoint
- Expected cleaning or regeneration interval at the declared load profile
- Expected element life at the declared duty
- Statement on other emissions and noise contribution
- Range of conditions within which these values apply
When you share this with several vendors at enquiry stage, you also make offers easier to compare. Everyone is quoting against the same operating conditions. Our article on nameplate photos for an RECD enquiry helps you gather Part A quickly.
How Will Performance Be Verified?
A guarantee is only enforceable if you agree in advance how it will be checked. Settle these points before the order:
- Backpressure: Measured at site during commissioning at defined load steps, using a calibrated instrument at agreed tapping points. Record the clean value for future reference.
- Particulate capture: Normally supported by the certification test report for the model. If your consent conditions or contract require site measurement, specify the laboratory, ideally one accredited by NABL, the method, who pays and what happens if the result is borderline. Our article on whether a smokeless DG set still needs particulate measurement explains why visual smoke is not a substitute.
- Cleaning interval: Verified from backpressure logs over an agreed observation period, compared against the declared load profile.
- Noise: Measured at stated points before and after installation, under similar conditions.
For the full acceptance process, see our article on Factory Acceptance vs Site Acceptance Tests for RECD projects. For checking the certification itself, use our guides on verifying a CPCB-tested RECD and reading an RECD test certificate.
What Happens if the Guarantee Is Not Met?
Define remedies before anything goes wrong. A reasonable sequence is:
- Joint investigation: Both parties check whether operating conditions were within the declared range, using logs and baseline records.
- Rectification: If conditions were within range, the vendor modifies, cleans, resizes or replaces the device at its cost within an agreed time.
- Re-test: Performance is re-checked using the agreed method.
- Financial remedy: If rectification fails, a pre-agreed price reduction or, in serious cases, return of the device and refund.
If conditions were outside the declared range, the responsibility shifts, but the vendor should still propose a technical solution at an agreed cost. This keeps the conversation practical instead of adversarial.
The performance guarantee and the warranty are related but different. The warranty covers defects; the guarantee covers results. Our guide on RECD warranty terms: parts, labour and exclusions covers the defect side.
Red Flags in Performance Guarantee Wording
- “Performance as per CPCB norms” with no mention of model, certification reference or conditions
- Backpressure stated “within limits” without naming whose limits or at what load
- Cleaning interval stated as a single number with no load profile
- “Subject to proper operation and maintenance” with no definition of either
- Guarantee that applies only “at rated load” when your set rarely exceeds half load
- No verification method, no remedy and no timeline
When you spot any of these, ask the vendor to restate the guarantee against your Part A conditions. A confident vendor will do so. One who refuses is telling you something useful. For broader vendor evaluation, see how to choose CPCB-approved RECD vendors and what a “maintenance-free” claim actually means.
Frequently Asked Questions
Is the certification test report enough as a performance guarantee?
It proves the model achieved the required performance under test conditions. It does not automatically cover your engine, load profile or exhaust system. Use it as the foundation and add site-specific conditions on top.
Which operating condition matters most?
For backpressure, the exhaust configuration and engine flow matter most. For cleaning intervals, the load profile and engine condition dominate. For compliance, engine identity and certification coverage come first.
Can a vendor refuse to guarantee performance at low load?
They can set a lower limit, which is reasonable for many technologies. What matters is that the limit is stated before purchase and that the offered solution suits your actual load profile.
Who should measure backpressure at commissioning?
Usually the vendor’s engineer, witnessed by your team and ideally your DG service provider, using a calibrated instrument at agreed points.
What if my operating conditions change after installation?
Inform the vendor in writing. Some changes, such as load growth within the declared headroom, should be covered. Others, such as dual-fuel conversion, may need a review of the guarantee.
Final Word
A performance guarantee is a contract between two descriptions of reality: yours and the vendor’s. When both are written down in the same document, disagreements become rare, and when they do happen, they are settled by data rather than opinion. Define the engine, the load, the fuel, the site, the exhaust and the maintenance regime, and the numbers in the guarantee start to mean something.
Aceget prepares site-specific guarantee data for every RECD offer. Explore our Retrofit Emission Control Devices, read about DG set emission regulations or get in touch with our engineers with your DG details.