Your Steam Boiler Is Not 80% Efficient — The Real Number Might Shock You

1. The Combustion Efficiency Myth

The boiler nameplate says 82%. The service engineer runs a flue gas analysis and confirms 81%. The energy audit report agrees. Everyone nods. Everyone is wrong.

Not wrong about the measurement. The measurement is correct. They are wrong about what it means.

What they measured is combustion efficiency — the percentage of fuel energy that makes it into the steam, right at the boiler shell. It accounts for flue gas losses and incomplete combustion. For a well-maintained diesel or bunker fuel boiler in the Philippines, 80–85% is typical and entirely believable.

But combustion efficiency is not the number that matters. The number that matters is delivered thermal efficiency — the percentage of fuel energy that actually reaches your process as useful heat. This is the energy that heats your product, your water, your CIP solution. Everything between the burner flame and the point of use is a loss.

In a typical Philippine food factory running steam at 7–10 bar, delivered thermal efficiency is 45–65%. In plants using steam sparging for tank heating — and there are many — it drops below 45%.

A pasta factory study illustrates this starkly. Two boilers showed combustion efficiencies of 81% and 80% respectively. Yet the heat losses from the boilers alone — before any distribution losses — were 18.65% and 19.47%. By the time that steam reaches the process, the factory is getting barely half the energy it paid for.

2. The Seven Steam Losses

Where does the energy go? Between the burner flame and the point of use, steam passes through a chain of losses. Each one is modest in isolation. Together, they are devastating.

1. Dry Flue Gas Loss (8–12%)

Hot combustion gases exit the stack carrying energy that never reached the water. Every 20°C reduction in flue gas temperature saves approximately 1% of fuel input. Philippine boilers commonly run flue gas temperatures of 180–250°C — well above the 120–140°C achievable with an economiser. Most plants in the Philippines do not have one fitted.

2. Hydrogen in Fuel Loss (2–3%)

When hydrogen in the fuel combusts, it forms water vapour. That vapour carries latent heat up the stack. This loss is fixed by the fuel chemistry — diesel and bunker fuel contain 10–13% hydrogen by mass. You cannot eliminate it, but you should know it is there when reading your combustion efficiency report.

3. Radiation and Convection Loss (1–3%)

The boiler shell is hot. It radiates and convects heat into the boiler room. In a 32°C Philippine ambient environment, the temperature difference is smaller than in a temperate climate, so radiation loss is marginally lower — but convection from air movement in open-sided boiler houses offsets this. Poorly insulated boiler shells and steam drums can push this to 3% or more.

4. Steam Distribution Loss (3–8%)

Steam travels through pipes from the boiler house to the process. Every metre of uninsulated pipe at 7–10 bar bleeds energy. In Philippine factories, where boiler houses are often 30–80 metres from the process, distribution losses of 5–8% are common. Damaged or missing insulation — eaten by rats, removed during maintenance and never replaced — makes this worse.

5. Steam Trap Losses (2–5%)

Steam traps remove condensate and non-condensable gases from the steam system. When they fail open, they pass live steam straight to the condensate return or, worse, to drain. A single failed-open DN15 trap at 7 bar wastes 50–80 kg/h of live steam. Most Philippine factories have never surveyed their traps. Industry data suggests 15–30% of traps in any given plant are failed.

6. Steam Coil Heat Exchanger Loss (5–10%)

When steam heats a process fluid through a coil or plate heat exchanger, the terminal temperature difference means not all steam energy transfers to the product. Fouled coils, undersized exchangers, and poor condensate drainage widen this gap. The condensate leaving the exchanger at 100–130°C still contains significant energy. If it is dumped to drain rather than returned to the boiler feedwater tank, that energy is lost entirely.

7. Steam Sparging Loss (10–20%)

This is the worst one. Steam sparging means injecting live steam directly into a tank of liquid — water for CIP, process liquor, or cooking vessels. It is extremely common in Philippine food factories because it is cheap to install and heats quickly.

The problem: every kilogram of steam injected into the tank becomes condensate mixed into the product. It cannot be recovered. The boiler feedwater tank receives no return. The plant must make up 100% of that steam as fresh treated water, heated from ambient. Flash steam from the vented tank carries additional energy to atmosphere.

In a sparging system, delivered efficiency routinely falls below 45%. For every peso of diesel burned, less than half reaches the product as useful heat.

3. See Your Losses — Interactive Sankey

Numbers in a table are one thing. Seeing the energy flow from burner to process — and watching the losses peel away at each stage — is something else entirely.

We built an interactive Sankey diagram that lets you input your own boiler parameters: fuel type, steam pressure, pipe length, insulation condition, trap failure rate, and heat delivery method. The tool calculates each loss and draws the energy flow in real time so you can see exactly where your fuel money goes.

Open Boiler Sankey Tool

4. The iHEAT Comparison

Once you see the real delivered efficiency of a steam system, the comparison to a Karnot iHEAT R290 heat pump is stark. The table below uses real Philippine energy prices: diesel at ₱72/L (10.12 kWh/L) and grid electricity at ₱10/kWh.

Read that bottom row again. The iHEAT does not just match the steam boiler. It delivers the same kilowatt-hour of useful heat for a fraction of the cost. A COP of 4.0 means that for every 1 kWh of electricity consumed, the heat pump delivers 4 kWh of thermal energy to your process.

For a factory currently spending ₱360,000/month on diesel for steam generation, switching the thermal load to iHEAT R290 heat pumps reduces that energy bill to approximately ₱57,000/month in electricity. The saving is ₱303,000 per month — ₱3.64 million per year.

5. SEC PFRS S2 — Your Boiler Is Now a Liability

Starting with FY2026, Tier 1 publicly listed companies in the Philippines must report climate-related financial disclosures under SEC PFRS S2, aligned with ISSB IFRS S2. Every litre of diesel your boiler burns is a Scope 1 direct emission that must be quantified, disclosed, and — increasingly — reduced.

The arithmetic is straightforward. One litre of diesel produces 2.68 kg CO₂e. A factory burning 5,000 litres per month emits:

5,000 L × 12 months × 2.68 kg = 160.8 tonnes CO₂e per year

That is 161 tonnes of Scope 1 emissions on your sustainability report — reportable, auditable, and visible to investors, lenders, and regulators. As carbon pricing mechanisms develop across ASEAN, those tonnes will carry a direct financial cost.

The Karnot iHEAT R290 eliminates this entirely:

• Scope 1: Zero. No combustion on site.
• Scope 2: Reduced by approximately 78% versus the diesel boiler, because the COP of 4.0 means 75% less purchased energy for the same thermal output.
• Refrigerant: R290 (propane) has a GWP of 3, compared to 675 for R32 or 2,088 for R410A. Negligible climate impact from fugitive emissions.

For full details on the reporting timeline and requirements, see our SEC PFRS S2 Compliance Guide.

6. What To Do Next

You now know that the number on your boiler nameplate is not the number that matters. Here are three concrete actions you can take this week: