Wall-Mounted vs Floor-Supported RECDs: How to Assess the Support Layout

A retrofit emission control device has to sit on something. That sounds obvious, yet the support is one of the least discussed parts of an RECD project. Owners compare filter efficiency, approval certificates and prices in detail, then leave the question of what holds the device up to the last site meeting, when the fabricator asks, “Wall or floor?”

The answer shapes far more than the steelwork. It decides how loads reach the building, how the exhaust pipe moves when it heats up, where technicians stand during service, how much floor the device takes and what happens to the wall or slab twenty years from now. This guide explains both options, gives a set of questions for judging the wall and the floor on your own site, and walks through two illustrative cases where the answers came out differently.

The Two Options in Plain Terms

Wall-mounted support

The device is carried by brackets fixed to a wall or a column. Most commonly these are steel cantilever brackets: horizontal arms projecting from a base plate that is anchored into the wall, sometimes with a diagonal strut beneath each arm. The device rests on saddles fixed to the arms, or hangs from them on clamps.

Wall mounting is popular where floor space is scarce, where the exhaust already runs along a wall towards a stack, or where the device needs to sit at a height to line up with the pipe.

Floor-supported layout

The device stands on its own frame: two or four legs, cross members and saddles, with base plates bolted to a concrete floor, plinth or pedestal. A variation is a skid, a flat steel base that sits on the floor and spreads the load over a wider area.

Floor support is the default in open yards, on plinths beside canopies and in generator rooms with enough floor area.

The hybrid

Many real installations mix the two. A floor frame carries most of the weight, while a wall tie or bracket at the top stops a tall device swaying. Or a wall bracket carries the device while a floor-mounted prop takes part of the load near the end of a long arm. Hybrids are often the most sensible answer, as long as both parts are designed to work together rather than added as an afterthought.

Why the Choice Is Structural Before It Is Practical

Weight does not disappear. It travels from the device into whatever supports it, and from there into the building. The two options send that load along very different paths.

Feature	Wall-mounted	Floor-supported
Where the load goes	Into the wall as a downward force plus a turning effect that tries to pull the top anchors out	Straight down into the floor or plinth
What resists it	Anchor bolts in tension and shear, and the wall material around them	Bearing on the floor; anchors mainly resist sliding and uplift
Most sensitive to	Wall material, wall thickness, anchor edge distances, bracket length	Floor slab capacity, soil under ground-bearing slabs, plinth size
Typical weak point	Anchors in hollow blocks or old brickwork	Thin slabs, slabs over voids, floors with trenches
Effect of a longer arm or taller frame	Turning effect grows with projection; anchors work much harder	Overturning risk grows with height; base must be wider or tied back

The most important line in that table is the first one for walls. A bracket that projects from a wall does not simply hang weight on it. The further the device sits from the wall face, the larger the turning effect at the base plate. That turning effect is resisted by the top anchors pulling and the bottom of the plate pushing. A device that would sit comfortably on the floor can overload a wall’s anchors if it is held a long way out.

Five Questions to Ask About the Wall

Before any wall bracket is drawn, the wall itself needs to pass a short interrogation. Walk up to it with the site engineer and work through these questions.

1. What is the wall made of?

This is the first and most decisive question. Reinforced concrete walls and columns accept properly designed anchors well. Solid brickwork can carry moderate loads with suitable anchors and enough edge distance. Hollow concrete blocks, aerated blocks, cavity walls and lightweight partitions are poor hosts for heavy, vibrating, hot equipment. Plaster hides everything, so if there is no drawing, drill a small test hole or look at an exposed edge.

2. Is it a load-bearing or a partition wall?

A partition wall is designed to stand up and carry its own weight. It is not designed to carry hundreds of kilograms on a bracket. Load-bearing walls and concrete shear walls are better candidates, but they are also part of the building’s structure, so any significant new load on them needs a structural engineer’s agreement.

3. How thick is it, and what is behind it?

Anchors need embedment depth and material behind them. A thin wall may not give enough depth. A wall with a corridor, a lift shaft or a neighbour’s property on the other side raises questions about drilling through, heat transfer and noise.

4. What is already fixed to it?

Cable trays, conduit, ventilation ducts, fire pipes and earlier brackets compete for the same face. Old anchor holes weaken the material near them. A wall covered in services may have no clear area large enough for a base plate with proper anchor spacing.

5. Will it stay, and can the anchors be placed with the right edge distances?

Walls in factories and commercial buildings change, so a partition due for removal is no home for a device. Anchors placed too close to the edge of a wall, a column corner or an opening can break out a cone of material. Anchor makers publish minimum edge distances and spacings for each product and base material. If the bracket must sit near a corner or a window, the wall may not be suitable even if it is solid concrete.

The general idea of how anchors work in concrete and masonry is explained in the anchor bolt article. For any real installation, the anchor maker’s technical data for the specific base material governs.

Five Questions to Ask About the Floor

The floor has its own interrogation.

1. Is it a ground-bearing slab or a suspended slab?

A ground-bearing slab rests on compacted soil and usually carries concentrated loads better than a suspended slab of the same thickness. A suspended slab, such as a podium, mezzanine or upper floor, spans between beams and needs a check, particularly if the frame legs land in the middle of a span.

2. What else is below?

Basements, cable trenches, fuel pipe ducts and drainage channels under the floor change its capacity. A frame leg that lands on a trench cover is landing on a steel plate, not on concrete.

3. Is there room without blocking anything?

A floor frame must not narrow escape routes, sit in front of electrical panels or block the generator’s own service doors.

4. Is a plinth needed?

A concrete plinth keeps base plates out of standing water and can spread load. Outdoors in heavy rain zones, it is close to essential.

5. Does the floor move?

Floors in yards may settle. Slabs near heavy machinery may vibrate. Expansion joints in large floors move with temperature. A frame that straddles a floor joint or sits on settling ground will see its alignment change over time.

The Exhaust Pipe Has Opinions Too

The support layout cannot be chosen in isolation from the pipe it carries. Three pipe-related factors often push the decision one way.

Height of the existing run. If the exhaust runs along a wall at 2.5 m above floor level, a wall bracket at that height keeps the device in line with the pipe. A floor frame would have to be tall, with the overturning and bracing issues that brings, or the pipe would need extra bends to drop down and climb back up. Each bend adds resistance, as our explainer on how exhaust backpressure affects a DG set describes.

Thermal growth. A hot device and its pipe grow in length. On either support type, one saddle should usually be fixed and the other should allow sliding, so expansion does not push on the engine or crack a weld. On a wall bracket, a sliding saddle also stops the expansion force from levering the anchors. The general behaviour of materials as they heat is covered in the thermal expansion article.

Vibration. Engine vibration travels along the exhaust. A flexible bellows near the engine absorbs most of it, but some always reaches the device. A wall can transmit that vibration into the building fabric, where it may be heard in rooms beyond. Floor frames on a ground slab usually transmit less to occupied spaces. Our guide on how to prevent generator vibration issues explains isolation basics.

Weighing the Options Side by Side

Consideration	Wall-mounted	Floor-supported
Floor space used	Little or none	A frame footprint plus clearance
Suitability for heavy devices	Limited by wall and anchors; long arms add stress	Good on a sound floor or plinth
Alignment with a high exhaust run	Natural	Needs a tall frame or extra bends
Vibration into the building	Higher risk, especially through thin walls	Lower on ground-bearing slabs
Heat effect on the structure	Wall surface behind the device heats up; finishes may discolour	Floor near the base may warm; usually less of an issue
Service access	Device is often high; needs a ladder or platform	Device is often at working height
Filter withdrawal	Arms may limit withdrawal direction	Usually easier to clear around
Impact protection	Out of reach of vehicles and trolleys	Needs bollards or kerbs in yards
Inspection of the support	Anchors hidden behind plates; harder to check	Base plates visible and easy to inspect
Future relocation	Leaves anchor holes and a patched wall	Frame can often be unbolted and moved

How Weight and Projection Change the Picture

A useful way to think about wall mounting is to picture the device’s weight acting at its centre, at some distance from the wall face. The anchors have to resist that weight multiplied by that distance. Double the distance and you double the turning effect, even though the device weighs the same.

This has practical consequences:

• Keep the device close to the wall. Every extra 100 mm of projection costs anchor capacity. Insulation thickness and clearance between the device and the wall add to projection, so include them in the drawing.
• Use struts or knee braces under long arms. A diagonal brace turns some of the bending into compression that the lower part of the wall can resist more easily.
• Spread the base plate vertically. A taller base plate with anchors further apart resists the turning effect better than a short, square one.
• Think about the removed filter. During service, the technician may lift the filter module out and set it down. If the arm is the nearest flat surface, it will be used as a shelf, adding load at the worst possible position.

For floor frames, the equivalent issue is height. A tall frame with the device at the top behaves like an inverted pendulum. Wind outdoors, seismic shaking or a knock from a trolley can tip it if the base is narrow. Widen the base, brace the legs or tie the top back to a wall or column.

The weight figures that feed into all of this come from the vendor. Ask for both the empty weight and the weight with insulation, accessories and a reasonable soot and ash load. Our article on why same kVA DG sets can need different RECDs explains why device size, and therefore weight, can vary between engines of the same rating.

Heat Behind the Bracket

Wall mounting places a hot device close to a building surface. Even an insulated device radiates some heat, and flanges, sensor bosses and access doors often run hotter than the insulated shell.

Over time, this can discolour and crack plaster, damage cable insulation running along the same wall and raise the temperature of the anchors themselves.

Practical steps include leaving an air gap between the device and the wall, fitting a reflective heat shield on the wall side, keeping cable trays away from the device zone and choosing anchors rated for the temperatures they will see. Our guide on common causes of generator overheating covers heat management in generator rooms more broadly.

Corrosion and Water

Outdoors, both support types need protection from rain and humidity. Each fails in its own way.

Wall brackets collect water at the top of the base plate, where it runs behind the plate and into anchor holes. Over years, corroding anchors in wet masonry can lose capacity without any visible sign on the surface. Seal the top edge of base plates and use corrosion-resistant anchors outdoors.

Floor frames stand in whatever water collects on the floor. Base plates on a plinth stay drier. Galvanised or well-painted steel, with drainage around the plinth, lasts much longer than bare steel on a flat floor.

Where dissimilar metals meet, such as stainless steel saddles on painted carbon steel arms, moisture can encourage galvanic corrosion. Isolating pads between the two help. Coastal and high-humidity sites need extra care; our guide on RECDs for water treatment plants discusses corrosion in wet surroundings.

Service Access: Where Will the Technician Stand?

Supports determine where people work. That deserves as much thought as the loads.

With a wall bracket

The device is usually above head height. Routine checks such as reading a backpressure gauge or looking for exhaust leaks need a ladder or a fixed platform, unless the display is relocated to floor level. Filter withdrawal may be blocked by the bracket arms in one direction and by the wall in another. Before approving a wall-mounted design, confirm which way the filter comes out and that nothing obstructs that path.

With a floor frame

The device is often at or near working height. Joints, sensors and clamps are easier to reach. The frame legs and cross members, however, can get in the way of a trolley used to carry the filter away, so plan which side stays open.

Either way, an RECD will need periodic cleaning and inspection for its whole life. Our RECD maintenance guide lists the tasks, and our companion article on service clearance around an RECD explains how much room each task needs.

A Decision Path

Work through these steps in order. Each one can rule an option out.

1. Get the device weight and dimensions from the vendor, including insulation, and the position of its saddles or mounting points.
2. Find the exhaust height and route where the device will sit. Note whether the pipe runs along a wall, at floor level or overhead.
3. Interrogate the wall using the five wall questions above. If the wall is hollow, lightweight, temporary or crowded with services, wall mounting is unlikely to be suitable without strengthening.
4. Interrogate the floor using the five floor questions above. If the floor is suspended over a void, crossed by trenches or needed for escape routes, floor support may be ruled out.
5. If both pass, compare the side-by-side table and decide which compromises matter least. Service access often tips the balance.
6. If neither passes on its own, consider a hybrid, a steel column-and-beam frame that carries the device independently of the wall, or a different device position along the exhaust route.
7. Ask a structural engineer to check the chosen arrangement and the anchors, especially for heavy devices, suspended floors or load-bearing walls.
8. Draw it. The support drawing should show anchors, base plates, fixed and sliding saddles, insulation thickness, heat shields and service zones.

When comparing quotations, ask each vendor to state the in-service weight, the wall projection, the anchor specification and the filter withdrawal side for their proposed support. Those answers are a quick test when choosing CPCB approved RECD vendors, and our step-by-step RECD installation process shows where support design fits into the overall project.

Illustrative Case One: Pharmaceutical Warehouse in Indore

The site

A 320 kVA set in a generator room at one end of a pharmaceutical storage building. The exhaust left the canopy and ran along the room’s rear wall at about 2.7 m height to a stack outside. Floor space in the room was tight, with the fuel day tank on one side and the main panel on the other.

The wall

The rear wall was a 230 mm reinforced concrete wall that formed part of the building’s structural frame. Drawings were available, a scan confirmed the reinforcement layout, and there were no services in the proposed bracket zone except one conduit that could be rerouted.

The floor

The generator room floor sat over a cable trench running beneath the area where a floor frame would have stood. The only floor space without a trench was in front of the panel, where the electrical working area had to stay clear.

The decision

Wall mounting. Two cantilever brackets with diagonal struts carried the device close to the wall face, with a 75 mm air gap and a reflective heat shield. The saddle nearer the engine was fixed; the far saddle slid on a low-friction pad. The structural engineer specified the anchor type and positions from the scan results. The backpressure display was moved to a bracket at eye level beside the door, and a fixed ladder with a small platform gave access to the clamps.

Because the facility handles temperature-sensitive pharmaceutical stock, change control documented each step; our guide on RECDs for pharmaceutical plants explains how that works. The 320 kVA DG set RECD page covers the rating used here.

Illustrative Case Two: Seafood Processing Unit in Kochi

The site

A 100 kVA canopy set in an outdoor yard beside a seafood processing building. The tailpipe left the canopy roof and turned horizontally towards the building wall, where a short stack had been fixed. Salt-laden air, monsoon rain and wash-down water were constant.

The wall

The nearest wall was the processing building’s external wall, built from hollow concrete blocks with a plaster finish. Behind it, inside the building, was a chilled packing room.

The floor

The yard had a ground-bearing concrete slab in good condition, with space beside the canopy that was not used for vehicle movement.

The decision

Floor support. A galvanised steel frame on a raised concrete plinth carried the device beside the canopy, with drainage around the plinth and stainless steel anchors. Wall mounting was rejected because hollow blocks were a poor anchor base, because vibration and heat would have reached the chilled room, and because water running down the wall would have attacked the anchors. A light tie from the top of the stack to a steel post kept it steady in monsoon winds. Isolating pads separated the stainless saddles from the galvanised frame.

Food plants have their own hygiene and wash-down constraints; our guide on RECDs for food processing units discusses them. See the 100 kVA DG set RECD page for this rating.

Warning Signs After Installation

Whichever support is chosen, check it during routine service. These signs suggest a support problem:

Sign	Possible cause	Action
Hairline cracks in plaster around a wall base plate	Anchor movement or overload	Stop using the bracket as a shelf; ask for a structural check
Rust staining below a base plate	Water behind the plate; anchors corroding	Seal the plate edge; inspect anchors
Device visibly lower at one end	Bracket arm bending or anchor creep	Check level against the installation record
Loose nuts on floor anchors	Vibration loosening	Retighten; consider lock nuts or vibration-resistant fixings
Frame legs standing in water	Poor drainage	Add a plinth or improve falls
Scuffed or bent frame members	Impact from trolleys or vehicles	Add bollards or kerbs
New noise in rooms beyond a wall	Vibration transmitted through the bracket	Check bellows condition and isolation pads
Sliding saddle seized	Corrosion or debris on the slide pad	Clean and free it before thermal stress damages the pipe

Our article on common RECD installation mistakes covers other problems that show up in the first months.

Compliance Note

The CPCB’s System and Procedure for Emission Compliance Testing of RECDs governs the approval of the device, not the steelwork that holds it. Support design is still part of doing the job properly: a device that sags, vibrates loose or blocks its own service access will not stay in good condition. For structural and fire matters in buildings, the BIS guide to using the National Building Code of India 2016 explains how the code is organised, and your structural and fire consultants will apply the relevant parts.

Frequently Asked Questions

Is it safe to mount an RECD on a wall?

It can be, on a suitable wall with properly designed brackets and anchors. Reinforced concrete walls and columns are the best hosts. Hollow blocks, lightweight partitions and walls crowded with services usually are not.

Which is better for a heavy RECD, wall or floor?

Heavy devices are generally easier to carry on a floor frame or plinth, because the load goes straight down. Wall mounting of heavy devices is possible but needs careful design to keep the projection short and the anchors within their capacity.

Why does one saddle need to slide?

Because the device and pipe grow in length when hot. If both ends are fixed, the expansion has nowhere to go and pushes on the anchors, the engine connection or the welds.

Can a floor frame be moved later?

Usually more easily than a wall bracket. Floor frames are often bolted down and can be unbolted, while wall brackets leave anchor holes that must be repaired. Our article on whether an RECD can be transferred to another diesel generator discusses relocation more broadly.

The Support Is Part of the Device

A well-chosen RECD on a poorly chosen support is a problem waiting for its moment. Ask what the wall is made of before drawing a bracket. Ask what lies under the floor before drawing a frame. Keep projection short, let one end slide, protect the steel and the anchors from water and heat, and decide where the technician will stand before the first bolt goes in. The right support is the one that keeps the device level, quiet and serviceable for as long as the generator runs.

Aceget’s site surveys include a support assessment of the wall and floor at every proposed device position, and our type-approved RECDs can be supplied with wall-bracket, floor-frame or hybrid supports to suit the site. To have your layout reviewed, talk to the Aceget team, or see the full retrofit emission control device range.