Every furnace obeys the same rule: the heat that goes in must come out somewhere. An energy balance writes that rule down, listing every source of heat and every place it ends up, so the useful share and the lost share become numbers instead of opinions. Without it, efficiency projects start from rumours about which loss is biggest, and the loudest suggestion wins. With it, engineers can size each loss, see which ones are recoverable and test whether a claimed quick win applies to their own furnace. Teams that want a balance built from live furnace data can watch a furnace balance close on real plant readings in a short session.
Write Down Where Every Unit of Furnace Heat Goes
iFactory AI builds a live heat-in, heat-out balance for each furnace, so losses are quantified and the quick wins are the ones the numbers support.
The Ledger: Heat In, Heat Out
A balance works like a ledger. Every entry on one side needs a matching entry on the other, and the totals must agree within a small residual.
| Heat In | Heat Out |
|---|---|
| Chemical heat of fuel | Useful heat in the steel, sensible and latent |
| Electrical energy, in electric furnaces | Heat carried by slag |
| Sensible heat of preheated air or charge | Flue or off-gas, sensible and chemical heat |
| Heat from oxidation of iron, carbon and silicon | Water cooling of panels, doors and roofs |
| Sensible heat of hot metal or scrap charged | Conduction and radiation from walls and roof |
| Other process inputs | Radiation through openings and scale formation |
| Total heat in | Total heat out, plus a small residual |
Each Furnace Type Loses Heat Differently
The dominant loss changes with furnace design, so the first question is always which furnace you are looking at.
Reheating Furnace
Excess air and high exit temperature carry heat up the stack. Door openings add radiation loss.
Electric Arc Furnace
Hot off-gas, cooling water and long power-off periods dominate the lost share.
Converter
Chemical heat in the off-gas and sensible heat in slag are the largest outputs besides the steel.
Ladle and Soaking Furnaces
Time spent holding at temperature drives losses through walls, lids and cooling.
See Your Own Furnace Balance Before You Plan a Project
Book a 30-minute session and iFactory AI will show heat in, heat out and each loss sized for a furnace on your plant.
Does the Balance Close? The Residual Test
The difference between heat in and the sum of identified outputs is the residual. A small residual means the balance can be trusted, and a large one means something is missing or mismeasured. Engineers can see a residual test in a live session before relying on any result.
Size Each Loss Before You Chase It
A loss is only worth chasing if a meaningful part of it can be recovered. For each loss the pale bar shows its size and the dark bar shows the recoverable part, both as illustrative units per 100 of heat input.
The Quick Win Board
Actions sort naturally by effort. Cheap operating fixes go first, and capital projects wait for the balance to justify them.
Six Measurements the Balance Needs
A balance is only as good as its inputs. These six measurements cover most of what a furnace engineer needs.
A Composite Scenario: One Tuning Day, One Step Down
A reheating furnace showed flue oxygen well above target. After burner tuning, daily GJ per tonne stepped down and stayed there. The columns use an illustrative index, with 100 as the starting level.
Where iFactory AI Fits
Fuel meters, furnace temperatures and production records live in separate systems. iFactory AI joins them and keeps the balance running.
Live Balance
Heat in and heat out are recalculated per heat, charge or shift.
Residual Monitoring
A rising residual warns of a drifting meter before it corrupts conclusions.
Loss Sizing
Each loss is sized and ranked by what part is plausibly recoverable.
Action Verification
After a fix, the balance shows which loss moved and by how much.
Frequently Asked Questions
How accurate does the balance need to be?
Accurate enough that the residual is small and the main losses are stable from one period to the next. A few percent residual is usually acceptable for decisions, while a large residual means a missing stream or a measurement problem. iFactory AI's team can help you set residual limits suited to each furnace type.
Can we build a balance for a batch furnace?
Yes, but the balance should be built over complete cycles, not instantaneous readings. Batch furnaces swing between charging, heating and holding, so averaging over a full heat or charge gives a meaningful result. The model can then compare cycles and show how holding time and delays change the lost share. Continuous furnaces are simpler because conditions are steadier.
Is a quick win of ten percent realistic for our furnace?
It depends entirely on where the furnace sits today. A furnace running with high excess air and long idle holding has more room than one already well tuned. Generic percentages are hypotheses, not promises. See how the balance tests such a claim using your own furnace readings in a short session.
What if some measurements are missing?
Start with what you have and mark the rest as estimates. Portable instruments can fill gaps for a short campaign, such as flue gas analysis or surface temperature surveys. The balance shows which missing measurement has the biggest effect on the residual, so you can decide which gap deserves a permanent instrument and which can stay an estimate.
How does this link to GJ per tonne and kWh per tonne?
The balance explains the intensity figure. GJ or kWh per tonne tells you how much energy a tonne used, and the balance shows where that energy went. After any fix, the same metric confirms the result. Ask support how balances feed your energy benchmarks for each furnace and line.
Turn Furnace Efficiency From a Debate Into a Balance Sheet
iFactory AI quantifies every furnace loss and shows which quick wins your data supports. Book a walkthrough to see it on your own furnace readings.
