A factory is not only a place that consumes energy. It is also a place that throws an enormous amount of it away. Every time fuel is burned or electricity is drawn to heat, melt, or dry something, a large share of that input leaves as heat rather than as product. That unused heat is what we call industrial waste heat.
What industrial waste heat actually is
Industrial waste heat is the heat left over once a process has done its job — or the heat that never made it into the job at all. The important point is that this energy has already been paid for. Capture it and put it back to work, and you gain energy with no extra fuel and no extra emissions.
It leaves the plant along three main routes.
| Escape route | Where it comes from | Why recovery is awkward |
|---|---|---|
| Flue gas | Combustion gas going up the stack | Released on the process schedule, not on demand |
| Cooling water | Water warmed while cooling the process | Too cool to return directly to the process |
| Equipment and product surfaces | Heat radiating off hot product and furnace walls | Spread across many points, hard to collect |
How much is actually wasted
The scale is larger than most people assume. Forman et al. (2016) estimate that roughly 20–50% of the energy going into industry is lost as waste heat. In the UK, some analyses put the figure at around half of all industrial energy use.
A percentage is abstract, so put it another way: between a fifth and a half of every unit of energy a plant buys ends up going out the stack or the cooling tower instead of into the product.
The picture in Korea
Here is a detail that surprises people. Korea only began estimating its total industrial waste heat recently. A 2023 study by the Korea Energy Economics Institute (Park and Oh) noted that the national figure had never been properly quantified, and produced the first estimate.
Counting only the heat rejected from kiln and furnace cooling, the study put the chemical sector at roughly 1.6 million TOE and the metals sector at roughly 440,000 TOE. That covers one process step alone — widen the scope to all industry and the number grows considerably. Low-grade heat around 100°C is the hardest part of it, and most of that is simply discarded.
Why it has gone unrecovered
Three barriers explain why so much of this heat is still thrown away.
- Temperature. If the waste heat is cooler than what the process demands, it cannot be fed straight back in. Low-grade heat runs into this immediately.
- Timing. When heat is available at a different time than it is needed, there is nothing to do but let it go.
- Distance. If the nearest user of that heat is far away, it cools off in transit.
For decades these three barriers made waste heat something you simply accepted losing.
Waste heat is a resource, not a byproduct
Change the framing and waste heat becomes what it really is: energy that already exists, at close to zero marginal cost. The question is how to hold on to it until it is needed. Each barrier has a matching answer — raise low temperatures with a heat pump, bridge a timing gap by storing the heat and discharging it later, and cover distance by containing the heat and moving it.
Of these, thermal energy storage — the thermal battery — is the one that closes the timing and temperature gaps at once, which is what turns previously unrecoverable heat into a usable resource. If storing heat is a new concept, the article below covers the fundamentals.
IsoTES®, developed by GIGAette, is a thermal energy storage system aimed at exactly this gap.
The bottom line
How much of this discarded heat industry manages to reclaim will shape how far it can cut both energy costs and emissions. Waste heat is not a byproduct to be disposed of — it is the largest undeveloped energy resource still sitting in plain sight. If you want to look at what your own plant is losing and what could be recovered, request a technical meeting.
Sources
- Park, S. and Oh, S. (2023), Analysis of Heat Consumption Characteristics in Industrial Complexes and Estimation of Waste Heat Potential, Korea Energy Economics Institute, Basic Research Report 23-11 — first national estimate of waste heat potential (chemical kiln/furnace cooling approx. 1.6 million TOE, metals approx. 440,000 TOE)
- Forman, C. et al. (2016), “Estimating the global waste heat potential,” Renewable and Sustainable Energy Reviews — global estimate of industrial waste heat (approx. 20–50% of industrial energy input)