---
title: "Heat rate"
description: "Heat rate is the fuel energy consumed per unit of electrical energy generated, measured in BTU/kWh (US) or kJ/kWh (everywhere else). Lower heat rate equals higher thermodynamic efficiency. Heat rate is the central economic KPI of every coal-fired and gas-fired power plant — a 1% rise in heat rate at sustained load costs the operator 1% more fuel per MWh forever."
canonical_url: "https://sylio.co/glossary/heat-rate"
last_updated: "2026-06-28T02:29:25.842Z"
---

**Heat rate** is the fuel energy consumed per unit of electrical energy generated, measured in BTU/kWh (US) or kJ/kWh (everywhere else). Lower heat rate equals higher thermodynamic efficiency. Heat rate is the central economic KPI of every coal-fired and gas-fired power plant — a 1% rise in heat rate at sustained load costs the operator 1% more fuel per MWh forever.

## Heat rate and convective-pass fouling

Heat rate degrades from many causes. The fouling-driven contribution is normally split between:

- **Economiser fouling** — feedwater pre-heat falls, steam-cycle efficiency drops
- **Air heater fouling** — combustion-air pre-heat falls, boiler efficiency drops
- **Superheater / reheater fouling** — outlet temperatures fall, turbine efficiency drops
- **Forced attemperation loss** of margin

A typical poorly-maintained coal-fired unit carries 2–4% heat-rate penalty from cumulative fouling. Aggressive cleaning, including [sonic horns](/glossary/sonic-horn) on convective surfaces, can recover 1–3% of that — equivalent to USD 1–5 million annual fuel saving for a 500 MW unit.

## How heat-rate recovery is monetised

Heat-rate recovery is the headline business case for sonic-horn retrofits on coal and biomass boilers. The savings flow directly through fuel cost; payback periods of 12–24 months are routinely quoted.

## Related terms

- [Boiler](/glossary/boiler)
- [Economiser](/glossary/economiser)
- [Air heater](/glossary/air-heater)
- [Convective pass / backpass](/glossary/convective-pass-backpass)
- [Sonic horn](/glossary/sonic-horn)