Retrofitting heat recovery into an operating factory is very different from designing it into a new facility.
The available space is already occupied. Production schedules cannot simply be paused. Existing equipment may have been modified several times, and drawings do not always reflect what is currently installed. Any new system must also work alongside the people, controls and processes that keep the factory running every day.
These constraints do not make industrial waste heat recovery impractical. They mean that the project must be designed around the live manufacturing process from the beginning.
A successful retrofit is not simply a matter of selecting a heat exchanger or heat pump. It requires a detailed understanding of where heat is generated, when it is available, where it can be reused and how the new equipment can be installed without compromising production.
What does a heat recovery retrofit involve?
Waste heat is energy leaving a process without performing any further useful work. It may be found in:
- Kiln, furnace or oven exhaust gases
- Dryer and curing chamber exhausts
- Hot air discharged through ventilation systems
- Steam, condensate or heated process water
- Refrigeration and compressed-air systems
- Cooling circuits and other process equipment
A waste heat recovery system captures some of this energy and transfers it to another useful demand.
Depending on the temperatures and processes involved, recovered heat could be used to:
- Preheat combustion or dryer air
- Heat process or cleaning water
- Supply curing chambers
- Support space heating
- Reduce boiler demand
- Provide a heat source for a high-temperature heat pump
- Generate electricity where temperature and scale make this viable
The engineering challenge is to connect the heat source to a suitable demand while protecting the reliability, safety and performance of the existing process.
Why live-site retrofits are challenging
In a new factory, equipment layouts, access routes, pipework and control systems can be developed together. In an existing plant, the new industrial energy recovery system must fit around infrastructure that is already in continuous use.
Several challenges need to be addressed early.
Production cannot be treated as secondary
Manufacturing output remains the site’s priority throughout the project. Installation work may need to be divided into phases and coordinated around maintenance windows, product changes or planned shutdowns.
Connections to critical exhaust ducts, hot-water networks or electrical systems should therefore be planned well in advance. Wherever possible, components can be manufactured and assembled off-site so that final connection work is completed within a controlled window.
The objective is not merely to minimise downtime. It is to avoid introducing unnecessary risk to production.
Existing drawings may not tell the full story
Factories evolve. Pipework is rerouted, equipment is replaced and temporary modifications can become permanent parts of the process.
Site surveys should verify:
- Actual duct and pipe routes
- Available plant-room and external space
- Structural loading capacity
- Electrical connection capacity
- Maintenance and lifting access
- Fire and emergency routes
- Existing control architecture
- Potential interfaces with production equipment
Three-dimensional surveys can be particularly useful in congested sites because they allow the proposed installation to be coordinated against existing services before fabrication begins.
Waste heat availability changes over time
A temperature reading taken during one site visit is not enough to design a reliable system.
Heat availability may change with production rate, product type, batch cycle, season, maintenance condition and operating practice. Exhaust streams may also contain moisture, dust or corrosive substances that influence equipment selection.
A proper feasibility study should assess:
- Temperature and flow rate
- Operating hours
- Variations across production cycles
- Moisture and contaminant levels
- Pressure limitations
- Existing energy consumption
- The timing of potential heat demands
This establishes the quantity and quality of recoverable energy, rather than relying on a theoretical maximum.
A practical approach to retrofitting heat recovery
1. Understand how the site operates
The first stage is process engagement, not technology selection.
Engineers should speak with production, maintenance, energy and health and safety teams to understand how the plant is actually operated. This often reveals constraints and opportunities that are not visible in drawings or utility data.
The assessment should identify where heat is being lost, but also where the factory is purchasing energy to create heat elsewhere. The strongest opportunities for industrial waste heat utilisation are usually found where a consistent source can be matched with a dependable nearby demand.
2. Measure the heat source and demand
Temporary or permanent submetering may be needed to build an accurate energy balance.
Measurements could include:
- Exhaust temperature and mass flow
- Humidity or water content
- Hot-water supply and return temperatures
- Fuel and electricity consumption
- Process cycle times
- Production throughput
- Boiler operating patterns
- Seasonal changes in demand
Source and demand must be considered together. Recovering a large quantity of heat has limited value if there is nowhere useful to send it at the time it is available.
Thermal storage can sometimes bridge this timing gap by allowing heat to be captured during one part of the production cycle and used later.
3. Select the appropriate recovery technology
Different heat sources require different solutions. Options may include direct air recirculation, gas-to-air or gas-to-water heat exchangers, heat recovery towers, thermal storage, heat pumps and waste-heat-to-power systems.
Low-grade heat should not automatically be dismissed. A high-temperature heat pump can upgrade heat from a relatively low-temperature source into useful hot water for drying, curing or other industrial processes.
Technology selection should consider more than nominal efficiency. The design also needs to account for:
- Required delivery temperature
- Part-load performance
- Source temperature variation
- Fouling and corrosion risk
- Cleaning and maintenance requirements
- Electricity and fuel prices
- Carbon intensity
- Equipment lifetime
- Available space and utilities
- Operational resilience
Product-independent evaluation is important because the best solution should be determined by the site, not by a predetermined piece of equipment.
4. Develop the process integration strategy
This is where a heat recovery concept becomes an operational project.
The design must establish how recovered energy will enter the existing process, how the old and new systems will interact and what happens if the recovery equipment is unavailable.
In many cases, existing boilers or burners remain available as backup or supplementary capacity. This can allow the recovered heat supply to be introduced progressively while maintaining production temperatures.
The integration design may include:
- Bypass routes and isolation valves
- Buffer or thermal storage tanks
- Backup heating arrangements
- New pumps, fans and heat exchangers
- Modifications to ducts or process chambers
- Control-system integration
- Metering and monitoring points
- Safe access for cleaning and maintenance
The proposed equipment must not create excessive backpressure, disrupt airflow or change the process in a way that affects product quality.
5. Design the installation around the live site
A buildable installation plan should be developed with the site team before work begins.
This includes confirming:
- Installation phases
- Shutdown and connection windows
- Contractor access
- Equipment delivery and lifting routes
- Temporary isolation requirements
- Working areas near live production
- Permit and safety arrangements
- Commissioning responsibilities
Large projects may benefit from installing new infrastructure in sections while the factory continues operating. Final connections can then be completed during short, carefully planned shutdowns.
At Wienerberger’s Warnham brick works, Heatcatcher delivered a system recovering heat and water from seven operational drying-chamber exhausts. The installation connected the exhaust network to a heat recovery tower and two 1.3 MW thermal high-temperature heat pumps. The recovered energy now supplies hot water at temperatures of up to 90°C to heating systems installed within the chambers.
Completing the retrofit while the factory remained operational required close communication, phased installation and continuing engagement with the site team. The project also demonstrates how energy recovery from waste heat can deliver wider operational benefits: recovered water is returned to the manufacturing process, while improved chamber airflow supports dryer operation.
6. Commission the system progressively
Commissioning should confirm more than whether the equipment switches on.
The system must be tested under realistic production conditions to establish:
- Heat recovered at different operating loads
- Temperatures delivered to the process
- Interaction with existing boilers or burners
- Control stability
- Effects on airflow and pressure
- Energy and carbon savings
- Product quality and production performance
- Safe response to faults or equipment shutdowns
A staged commissioning period allows control settings to be refined without placing unnecessary pressure on the manufacturing process.
7. Monitor and optimise performance
Industrial process waste heat recovery is rarely fully optimised on its first day of operation.
Production conditions change, operators learn how the new system responds and additional opportunities may become visible once reliable data is available. Metering should therefore be included in the original design.
Useful performance indicators include:
- Heat captured and delivered
- Fuel displaced
- Electricity consumed
- System efficiency
- Carbon emissions avoided
- Water recovered
- Energy use per tonne of product
- Equipment availability
- Effect on cycle times and production output
Continued monitoring helps verify the business case while identifying adjustments to operating schedules, temperatures, storage capacity and control logic.
How can retrofit risk be reduced?
The greatest risks often arise from incomplete site information, poor process integration or insufficient engagement with the people operating the plant.
Risk can be reduced through:
- Early involvement of production and maintenance teams
- Detailed site measurements and energy monitoring
- Front-end engineering design before procurement
- Realistic modelling of source and demand variations
- Off-site fabrication where practical
- Clearly defined shutdown windows
- Retention of backup heating capacity
- Progressive commissioning
- Operator training and documented maintenance plans
- Post-commissioning monitoring and optimisation
These measures may require more preparation, but they reduce the likelihood of late design changes, installation delays and operational disruption.
Heat recovery within a wider decarbonisation strategy
Waste heat recovery is one part of industrial decarbonisation, but it is often one of the most practical places to begin.
Improving industrial energy efficiency reduces the amount of energy that must later be supplied through electrification, alternative fuels or other heat decarbonisation solutions. It can therefore lower both emissions and the future cost of replacing fossil-fuel heat.
For energy-intensive sectors such as ceramics, some emissions also arise from the chemical transformation of raw materials. These process emissions may ultimately require measures such as carbon capture, utilisation and storage. Heat recovery does not replace carbon capture where process emissions are unavoidable. Instead, it reduces avoidable fuel consumption and ensures that energy is used more efficiently before more complex solutions are considered.
Can heat recovery be installed without stopping production?
In many cases, yes, but “without stopping production” does not mean that no isolation or connection windows will ever be required.
The realistic objective is to complete most construction alongside normal operations, then coordinate a limited number of planned interventions for final connections and commissioning. Whether this is possible depends on the layout, process, safety requirements and points at which the new system connects to existing equipment.
That is why live-site installation planning must begin during the feasibility and design stages, not after equipment has been ordered.
From wasted heat to a working asset
A successful retrofit begins with the manufacturing process rather than the recovery technology.
The strongest waste heat recovery systems are those that fit the site physically, match its real operating patterns and make life easier—not harder—for the production team. When engineering design, installation planning and operational engagement are treated as one continuous process, heat that was previously discharged can become a dependable source of lower-carbon energy.
Heatcatcher supports manufacturers from initial site assessment and feasibility studies through front-end engineering design, turnkey delivery, commissioning and ongoing optimisation.
If your site is rejecting heat while continuing to purchase gas, oil or electricity for another process, the first step is to establish whether those two energy flows can be connected.