RECD Insulation and Heat Shields: What Should the Site Plan Cover?

Ask ten installers how to insulate a retrofit emission control device and most will describe a material: mineral wool, ceramic blanket, aluminium cladding, fabric jackets. Ask what the insulation is supposed to achieve on that particular site and the answers get shorter. Yet the material is the last decision, not the first. Before anyone orders a roll of blanket, the site plan should say what is hot, who or what is near it, what must stay hot, what must stay cool and how the whole arrangement will be inspected for the next fifteen years.

This article sets out the ten items that a good insulation and heat shield plan should cover for an RECD installation. Each item is a short section you can copy into a site plan, a tender document or a review checklist. A worked example at the end shows how the items fit together on a real-world style site.

Why Insulation Around an RECD Has Several Jobs at Once

Insulation on an exhaust system is asked to do four things, and on any one site some matter more than others.

Job	What it protects	Where it matters most
Keep heat in the gas	The filter’s ability to burn off soot	Pipe between engine and device; the device itself
Keep people safe	Hands, arms and legs from burns	Anywhere a person can touch the system
Keep heat out of the room	Ventilation load, nearby equipment, comfort	Indoor generator rooms, basements, enclosed sheds
Protect nearby materials	Cables, plastics, finishes, combustibles	Close to walls, cable trays, roofs and stored goods

These goals do not always point the same way. Insulating the pipe upstream of the device helps regeneration and personnel safety together. Insulating the device itself helps regeneration but may make its housing hotter inside the insulation. A heat shield protects a cable tray but may trap heat around a flange. The plan exists to resolve these trade-offs on purpose rather than by accident.

The filter side of the argument is explained in our guide on what an RECD is and how it works, and the background to particulate filters in what a diesel particulate filter is and how it helps.

Item 1: A Surface Temperature Map

The plan should start with a simple drawing showing the expected surface temperature of every part of the exhaust system when the set runs at full load, uninsulated.

What to show

• The engine outlet and bellows
• Each pipe section, with its expected gas temperature
• The device housing, including inlet and outlet cones
• Flanges, sensor bosses, access doors and clamps
• The downstream pipe, silencer if any, and stack

Where the numbers come from

The engine maker’s data gives exhaust temperature at the turbo outlet. The device vendor can supply housing temperatures in normal running and during regeneration. Temperatures fall along uninsulated pipe, but on short indoor runs they fall slowly.

Why it matters

Every later decision depends on this map. It shows where burns are possible, where heat will radiate into the room and which nearby items are at risk. The general behaviour of heat leaving a hot surface by radiation and convection is described in the thermal radiation article.

Item 2: Personnel Protection Zones

The second item marks where people can reach the hot surfaces.

Define the reach zone

A common approach is to treat any hot surface within normal reach of a standing person, and within reach from walkways, ladders and platforms, as needing protection. Surfaces high above walkways, inside guarded enclosures or behind fixed barriers may need none for personnel purposes.

Choose the protection

Protection type	When it fits	Notes
Full insulation with cladding	Surfaces people may brush against regularly	Also helps keep heat in the gas
Personnel guard (perforated metal or mesh cage)	Where insulation is unwanted, for example over a bellows or a sensor	Keeps hands away while letting heat escape
Removable jacket	Flanges and access points that need inspection	Must be refitted after service
Barrier or rail	Large surfaces where insulation is impractical	Prevents approach rather than covering the surface
Warning signs	Everywhere hot surfaces remain exposed	Supplement, never a substitute

The plan should state a target maximum touch temperature for the outer surface of insulation or guards in the reach zone, agreed with the site’s safety team.

Include service positions

Technicians kneel, lean and reach into places nobody walks past. A flange behind the device may be out of reach in normal operation but right beside a technician’s shoulder during filter removal. Mark service positions on the plan and protect around them too.

Item 3: Insulation Scope by Section

The third item is a table listing every section of the exhaust and whether it will be insulated, and why.

Section	Insulate?	Main reason
Turbo outlet to bellows	Usually no, or engine maker’s heat shield only	Engine makers often restrict insulation on turbochargers and manifolds
Bellows	Removable blanket or guard only	Rigid insulation restricts movement
Pipe from bellows to device	Yes	Keep gas hot; personnel protection
Device housing	Usually yes, with removable sections	Keep filter hot; reduce room heat
Device flanges and clamps	Removable jackets	Allow inspection and filter removal
Pipe after the device, indoors	Often yes	Personnel protection and room heat
Pipe after the device, outdoors	Depends on reach and condensate	Personnel protection; reduce condensation at the outlet
Silencer	Depends on design and noise needs	Some silencers are supplied pre-insulated
Stack above roof level	Usually no unless reachable	Weather and inspection outweigh benefit

The table removes ambiguity. Without it, installers insulate what is easy and skip what is awkward, which is often the reverse of what the site needs.

The regeneration argument for upstream insulation is strongest for sets that run lightly or briefly. Our guides on choosing an RECD for a generator running at low load and whether an RECD suits a DG set that runs only occasionally explain why.

Item 4: Material and Cladding Specification

Only now does the plan turn to materials.

Insulation material

Exhaust insulation must be rated above the maximum surface temperature it will see, including regeneration peaks. Common choices include high-temperature mineral wool, ceramic fibre and glass-fibre blankets, and composite mattresses with high-temperature fabric faces. The plan should state:

• Material type and temperature rating
• Thickness for each section, chosen to meet the target outer temperature or heat loss
• Density, where it affects performance
• Any health and handling precautions for the fibre type

Cladding

Outer cladding protects the insulation from damage and weather. Indoors, aluminium or stainless sheet is common. Outdoors, cladding must shed water, with overlaps arranged so rain runs off rather than in. Joints should face downward on horizontal runs and laps should run downhill.

Fixings

Bands, rivets, screws and wires should suit the temperature and the environment. Galvanised fixings near hot surfaces, or carbon steel fixings on stainless cladding in coastal air, can corrode quickly. Our guide on choosing an RECD for coastal salt-laden environments explains why material pairing matters near the sea.

Item 5: Removable Jackets at Inspection Points

An RECD is serviced throughout its life. Insulation that has to be cut off to reach a flange will be cut off and not put back properly.

Where removable jackets go

• Device inlet and outlet flanges
• Filter access clamps or doors
• Sensor ports and pressure tappings
• Bellows connections
• Drain points

What makes a good jacket

• Fastenings that can be undone and redone by hand, such as straps, buckles or lacing hooks
• A label or tag showing its position, so jackets are not swapped
• Overlap with the fixed insulation so no hot gap remains
• A material suited to repeated handling

The RECD maintenance guide lists the tasks that need access; the plan should place a jacket at each of those points.

Item 6: Heat Shields for Nearby Things

Insulation reduces heat at the source. Heat shields protect specific items near the source. The plan needs both.

What usually needs shielding

• Cable trays and conduits running near the device or pipe
• Fuel lines and day tanks
• Plastic pipes for water or drainage
• Electrical panels and control boxes
• Building finishes such as plaster, paint and false ceilings
• Structural members whose fire protection could be affected by sustained heat
• Sensors and cables belonging to the device itself

How shields work

A shield is usually a metal sheet, often reflective or perforated, placed between the hot surface and the item to be protected, with an air gap on both sides. The air gaps are what make it effective: a shield in contact with the hot surface simply becomes another hot surface. The general idea of reflecting and blocking radiant heat is covered in the heat shield article.

Planning rules

• Mark each protected item on the plan, with its distance from the hot surface
• State the shield type, its size and the air gaps
• Fix shields to the structure, not to the hot pipe, where possible
• Check that shields do not trap heat around flanges or sensors that rely on air cooling
• Do not let shields block filter withdrawal or service access

Item 7: Room Heat Load and Ventilation

Every watt that leaves the exhaust surfaces ends up in the generator room or canopy. The ventilation system must remove it, along with the much larger heat from the engine and alternator.

What the plan should state

• The estimated heat released by the exhaust system and device with the proposed insulation
• Whether the existing ventilation can remove it at the highest expected ambient temperature
• Any changes to fans, louvres or airflow paths

Why the retrofit changes the numbers

An RECD adds a large hot surface to the room if it is indoors. Without good insulation, it can noticeably raise room temperature, which in turn reduces engine performance and can trigger high-temperature alarms. Our articles on common causes of generator overheating and summer maintenance tips to prevent overheating explain the consequences, and the guide on assessing an RECD for very hot ambient conditions covers sites where the margin is already thin.

Item 8: Fire and Combustible Materials

Hot exhaust surfaces and combustible materials do not belong together.

What to check

• Distances from the device and pipe to timber, cardboard, stored goods, fabric and plastics
• Oil-soaked insulation risk near the engine, where leaks can wick into insulation and later ignite
• False ceilings and wall linings above or beside the exhaust
• Fire-rated walls and floors the exhaust passes through, and their fire-stops

What to include in the plan

• Minimum clearances to combustibles, agreed with the site’s fire consultant
• Use of non-absorbent or oil-resistant facing on insulation near oil sources
• Fire-stop details at each penetration, rated for the temperature and movement
• A housekeeping rule that nothing is stored near the exhaust

Building fire matters in India are governed by the National Building Code; the BIS guide to using the National Building Code of India 2016 explains how it is organised. Your fire consultant applies the relevant parts.

Item 9: Moisture and Corrosion Under Insulation

Insulation that stays wet does two kinds of harm. It stops insulating well, and it holds water against the pipe, where corrosion proceeds out of sight. The problem is common enough in industry to have its own name, described in the corrosion under insulation article.

Plan to keep it dry

• Weatherproof cladding outdoors, with sealed laps and end caps
• No insulation on low points where condensate collects, unless drainage is provided
• Drain holes at the lowest points of cladding so any water that gets in can get out
• Sealed penetrations where supports, sensors and brackets pass through cladding

Plan to look under it

• Inspection windows or removable sections at the most likely corrosion points
• A schedule for periodic removal and inspection, especially on carbon steel outdoors
• Thickness checks at the same points over time

Humid and wash-down environments need extra care. Our guide on RECDs for water treatment plants discusses corrosion in wet surroundings, and our companion post on protecting RECDs from rainwater and condensation covers the water side in more depth.

Item 10: Movement, Signage and Handover

The last item ties insulation to the rest of the installation.

Movement

Insulation must not lock sliding saddles, guides or bellows. Cladding needs expansion gaps at bends and long straights. The flexible bellows guide notes that rigid wrapping over a bellows is a common cause of early failure, and our companion guide on thermal expansion planning explains how the whole run moves.

Signage

Hot surface warning signs at every exposed hot area and at access points.

Handover

• A drawing showing insulation scope, jacket positions and shield positions
• The material data for insulation, cladding and jackets
• Instructions for removing and refitting jackets
• The inspection schedule for corrosion under insulation

The Plan on One Page

Here is a summary template that can head the full plan.

Item	Decision	Owner
1. Surface temperature map	Attached drawing, full load and regeneration	Vendor
2. Personnel protection zones	Reach zone marked; target outer temperature agreed	Safety team and vendor
3. Insulation scope	Section-by-section table	Vendor
4. Materials and cladding	Specification attached	Vendor
5. Removable jackets	Positions listed; labelled	Vendor and installer
6. Heat shields	Protected items listed with shield details	Vendor and site engineer
7. Room heat and ventilation	Heat estimate; ventilation check	Site engineer
8. Fire and combustibles	Clearances and fire-stops agreed	Fire consultant
9. Moisture and CUI	Drainage, sealing and inspection plan	Vendor and maintenance team
10. Movement, signage, handover	Gaps, signs and documents	Installer

Common Gaps Seen in Insulation Plans

Insulating the bellows rigidly

Wrapping a bellows tightly turns it into a rigid pipe. Use a removable blanket or a guard.

No jackets on flanges

Flanges get insulated with the pipe and cut open at the first service. Plan removable jackets from the start.

Shields fixed to the pipe

A shield bolted to a hot pipe radiates heat itself. Fix shields to the structure with air gaps.

Ignoring regeneration temperature

Insulation chosen for normal running can be overheated during regeneration. Use the higher figure.

Forgetting the outdoor water path

Unsealed cladding laps outdoors let rain in, and the insulation becomes a sponge.

Insulating the turbocharger

Many engine makers do not allow insulation over turbochargers or manifolds, because it can overheat components. Follow the engine maker’s instructions.

Several of these appear on our wider list of common RECD installation mistakes.

A Walkthrough: Business Hotel in Hyderabad

This is an illustrative case.

The site

• A 250 kVA set in a basement generator room beneath a business hotel’s service wing
• The RECD was to sit on a floor frame 2 m from the engine, with 6 m of pipe from the device to a shaft riser
• Above the generator room, the hotel laundry; beside it, the main electrical room separated by a block wall
• Cable trays ran along the ceiling, 600 mm above the planned pipe route

How the plan was built

Item 1. The vendor provided full-load and regeneration temperatures. The device housing and the first 2 m of pipe were the hottest surfaces.

Item 2. The whole room was a reach zone because the space was tight and technicians moved around the set. A maximum outer surface temperature was agreed with the hotel’s engineering head.

Item 3. Insulation was planned from the bellows connection to the shaft riser, including the device housing. The bellows got a removable blanket.

Item 4. High-temperature mineral wool with stainless cladding, chosen because of humidity from the laundry above.

Item 5. Removable jackets at both device flanges, the filter access clamp, two sensor ports and the drain.

Item 6. A perforated stainless heat shield was hung from the ceiling slab beneath the cable trays along the full pipe route, with air gaps above and below. A second shield protected the block wall facing the electrical room.

Item 7. The heat estimate showed the insulated system added only a modest load. The existing ventilation was adequate, but the louvre filters were cleaned and a room temperature sensor added.

Item 8. A storage rack for spare filters and consumables was moved out of the room.

Item 9. Cladding laps were sealed, and an inspection window was placed at the base of the riser where condensate could collect.

Item 10. Hot surface signs were fixed, and the maintenance team received a laminated card showing jacket positions.

The outcome

After commissioning, room temperature at full load stayed close to the pre-retrofit level, cable tray surface temperatures stayed low and the hotel’s engineering team found filter access straightforward because the jackets came off by hand. Hotels have their own constraints around guest areas and timing; our guide on RECDs for hotels covers them, and the basement DG room planning guide addresses the space and access side. The 250 kVA DG set RECD page shows the rating used here.

Questions for the Vendor

1. What housing temperature does the device reach during regeneration?
2. What insulation does the device come with, and what must be added on site?
3. Which parts must stay uninsulated, and why?
4. Where do you recommend removable jackets?
5. What outer surface temperature will the insulated system reach in our room?
6. How much heat will the system add to the room with your proposed insulation?
7. What inspection do you recommend for corrosion under insulation?

The answers also make a good comparison point when choosing CPCB approved RECD vendors.

Compliance Note

Device approval sits under CPCB’s System and Procedure for Emission Compliance Testing of RECDs. Insulation and shields are not approval items, but they affect how well the device regenerates, how safe the installation is and how it looks to an inspector. Keep the plan with your installation records. Our guide on what happens during a pollution control board inspection explains what inspectors tend to look at.

Frequently Asked Questions

Does an RECD need to be insulated?

In most installations, insulating the device and the pipe upstream of it helps keep the filter hot enough to burn off soot and reduces burn risk and room heat. The vendor’s instructions should say what is supplied and what must be added.

What is the difference between insulation and a heat shield?

Insulation wraps the hot surface to reduce heat leaving it. A heat shield sits between the hot surface and a specific item, with air gaps, to protect that item.

Can I insulate the flexible bellows?

Only with a removable blanket or a guard that does not restrict movement. Rigid insulation over a bellows shortens its life.

Should the turbocharger be insulated?

Follow the engine maker’s instructions. Many do not allow insulation over turbochargers or manifolds.

Why do flanges need removable jackets?

Because they are opened for inspection and filter removal. Fixed insulation gets cut and is rarely restored properly.

Can insulation cause corrosion?

Wet insulation can hold water against the pipe and cause corrosion out of sight. Weatherproof cladding, drainage and periodic inspection prevent it.

Plan the Heat, Then Choose the Blanket

Good insulation around an RECD is the visible end of a set of decisions about heat, people, nearby equipment, fire, water and future service. Make those decisions in a plan, item by item, and the material choice becomes straightforward. Skip them, and even expensive insulation can end up in the wrong place, cut open, soaked or wrapped around the one component that needed to stay free.

Aceget prepares a surface temperature map and insulation and shield plan for every RECD installation, and supplies devices with removable jackets at service points. To review the heat planning on your site, contact Aceget, or see the retrofit emission control device range.