A one percent rise in heat rate on a 200 MW gas turbine can quietly add well over a million dollars a year in extra fuel spend, and most plants do not notice until the quarterly fuel bill lands. Heat rate creeps upward from a handful of overlapping causes — compressor fouling, hot gas path wear, inlet pressure loss, and combustion tuning drift — and each one hides behind a different set of control room readings. Left untracked, these losses compound quietly for months before anyone connects rising fuel consumption to a specific root cause. This page breaks down where heat rate degradation actually comes from, how much of it is recoverable, and how plants are catching it early — see how it works on your fleet through iFactory support.
Power Generation · Heat Rate Analytics
Your Turbine Is Burning More Fuel Than It Should — And The Control Room Can't See Why
Heat rate degradation rarely shows up as one clear fault. It shows up as a slow upward drift across dozens of readings that no single operator is watching all at once.
Baseline Heat Rate9,850 kJ/kWh
Current Heat Rate10,140 kJ/kWh
Degradation2.9%
Likely CauseCompressor Fouling
1–3%
Typical annual heat rate degradation on an unwashed, uninspected gas turbine
70–80%
Share of total degradation that is recoverable through washing and cleaning alone
$200K+
Extra annual fuel cost from a single unaddressed percentage point of heat rate loss
30–40K
Fired hours in a typical time-between-overhaul cycle where degradation accumulates
Root Cause Breakdown
The Four Places Heat Rate Actually Leaks From
Heat rate degradation is rarely one problem. It is the sum of several component-level losses, each with a different recovery path and a different urgency level.
Compressor Fouling
Airborne particulate builds up on compressor blades, reducing airflow and pressure ratio. This is the single largest source of recoverable heat rate loss and the fastest to correct with washing.
Hot Gas Path Wear
Coating spallation, tip clearance growth, and creep elongation in nozzles and buckets reduce expansion efficiency. Most of this loss is non-recoverable without an overhaul.
Inlet & Exhaust Losses
Clogged inlet filters and rising exhaust backpressure both quietly increase heat rate by forcing the compressor and turbine to work against added resistance.
Combustion Tuning Drift
Fuel nozzle wear and control schedule drift push firing temperature and exhaust temperature spread away from their optimal tuning point, quietly costing efficiency.
See Which Component Is Driving Your Heat Rate Up.
iFactory separates recoverable losses from non-recoverable wear automatically, so your team fixes the right problem instead of guessing.
Recoverable vs. Non-Recoverable
Why Two Turbines With the Same Heat Rate Loss Need Different Fixes
Degradation Type
Typical Driver
Correction Path
Recoverable
Compressor fouling, filter loading, minor deposit buildup
Online and offline compressor washing, filter replacement
Partially Recoverable
Combustion tuning drift, fuel nozzle wear
Combustion tuning correction during a scheduled outage
Non-Recoverable
Tip clearance growth, coating spallation, creep elongation
Component repair or replacement during a hot gas path inspection
Structural
Seal wear, inlet duct leakage, exhaust plenum degradation
Mechanical repair identified through trending, not a single test
Benchmarking
How to Tell If Your Heat Rate Drift Is Normal or a Warning Sign
Every gas turbine loses some performance between overhauls. The question that matters operationally is whether the current drift matches the expected curve for your fleet, or whether it has broken away from it.
Year 1
Fastest degradation phase. Expect 1–2% heat rate increase as initial fouling and coating oxidation establish a baseline.
Years 2–4
Degradation rate slows if washing and inlet filtration are maintained on schedule. Drift beyond 3% total signals a missed correction.
Pre-Overhaul
Non-recoverable component wear becomes the dominant driver. Continuous trending tells you how much is fixable before the outage.
Correction Playbook
The Four-Step Sequence Plants Use to Close a Heat Rate Gap
Correcting heat rate loss works best as a sequence, not a single action. Skipping the verification step is the most common reason a wash or repair looks like it didn't help when it actually did.
Screen
Compare corrected heat rate against design conditions to confirm real degradation exists rather than an ambient temperature or fuel heating value effect.
Isolate
Trend pressure ratio, exhaust temperature, and firing temperature together to separate compressor-side loss from hot-section wear before choosing a fix.
Correct
Apply the matching fix — online or offline washing for fouling, combustion tuning for drift, or a scoped repair for confirmed hot-section wear.
Confirm
Re-run a corrected heat rate check within 24 to 72 hours of the action to confirm how much of the loss was actually recovered before closing out the work order.
Reading the Control Room Right
The Readings That Change Before Heat Rate Does
Heat rate itself is a lagging indicator — by the time it visibly moves on a trend chart, the underlying cause has usually been developing for days or weeks. A handful of upstream readings move first and are worth watching on their own.
01
Compressor pressure ratio — the earliest and most reliable signal that fouling is beginning to restrict airflow.
02
Exhaust temperature at constant load — a rise here at unchanged load points toward hot-section wear rather than compressor fouling.
03
Inlet filter differential pressure — a slow climb here adds a hidden heat rate penalty that a wash alone will not fix.
04
Fuel gas heating value — a shift in supply gas composition can mimic degradation on a heat rate chart even when the turbine itself is healthy.
From the Plant
What Changed Once Degradation Was Tracked by Cause
We knew heat rate was drifting up every quarter, but every review turned into a debate about whether it was fouling, ambient conditions, or the fuel gas heating value. Once we started trending pressure ratio, exhaust spread, and firing temperature against a clean baseline, the fouling component separated itself from the wear component almost immediately. We recovered most of the loss with a wash we would have delayed another two months.
— Performance Engineer, Combined Cycle Power Plant
Frequently Asked Questions
Gas Turbine Heat Rate — Common Questions
How much heat rate degradation is considered normal in a single year?
Most heavy-duty gas turbines lose roughly one to two percent of design heat rate in their first year of operation as initial fouling and minor coating oxidation set in, with the rate typically slowing in following years if washing and filtration are maintained. Anything materially above that range within a normal operating profile usually points to a specific, correctable cause rather than expected wear.
Book a demo to see your unit's degradation curve against fleet benchmarks.
Can heat rate loss be fully recovered without an overhaul?
A large share of typical heat rate loss, often the majority in a well-maintained unit, comes from compressor fouling and inlet restriction, both of which are recoverable through washing and filter changes without touching the hot section. The remaining loss from tip clearance growth and coating wear generally requires a hot gas path inspection or overhaul to fully correct.
Why do two identical turbines at the same plant degrade at different rates?
Duty cycle differences drive most of the variation — a unit that cycles frequently accumulates thermal fatigue and tip clearance growth much faster than a baseload unit running steady state, even with identical fired hours. Ambient air quality, inlet filtration condition, and wash discipline also vary meaningfully between units even on the same site.
What is the fastest way to isolate whether fouling or hot section wear is driving heat rate loss?
Trending compressor pressure ratio alongside exhaust temperature and firing temperature over time typically separates the two causes clearly, since fouling shows up as a pressure ratio drop while hot section wear shows up as elevated exhaust temperature at constant load. Continuous monitoring resolves this faster and more reliably than a single field test.
How often should a plant benchmark its heat rate against design conditions?
Monthly benchmarking against corrected, ambient-adjusted design heat rate is enough to catch most degradation trends before they compound into significant fuel cost, though high-fouling or high-cycling sites benefit from continuous rather than periodic tracking.
Contact support to set up corrected heat rate benchmarking for your fleet.
Stop Paying For Fuel Your Turbine Shouldn't Need
Continuous heat rate trending, automatic cause separation, and benchmark-driven correction — built for the way gas turbines actually degrade.
