---
title: "Furnace"
description: "The furnace is the radiant combustion chamber of an industrial boiler — the space where the burner flame develops, fuel combusts, and the bulk of the heat release happens. Furnace temperatures vary by fuel and design: 1,300–1,700 °C in PC boilers, 850–900 °C in CFB, 900–1,100 °C in WtE grate boilers."
canonical_url: "https://sylio.co/glossary/furnace"
last_updated: "2026-06-28T02:29:26.009Z"
---

The **furnace** is the radiant combustion chamber of an industrial boiler — the space where the burner flame develops, fuel combusts, and the bulk of the heat release happens. Furnace temperatures vary by fuel and design: 1,300–1,700 °C in [PC boilers](/glossary/pc-boiler), 850–900 °C in [CFB](/glossary/cfb-boiler), 900–1,100 °C in [WtE](/glossary/waste-to-energy) grate boilers.

## Heat transfer

Furnace heat is absorbed almost entirely by radiation onto the [waterwall](/glossary/waterwall) tubes forming the furnace enclosure. The flue gas leaves the furnace through a defined nose or screen and enters the [convective pass](/glossary/convective-pass-backpass) where conductive heat transfer dominates.

## Fouling at the furnace–convective interface

The transition from the radiant furnace to the convective pass — sometimes called the *furnace outlet* or *nose* — is where [slag](/glossary/slagging) is most likely to accumulate. Hot ash particles approaching this interface lose energy fast enough to bond onto cooler tube surfaces. [Sonic horns](/glossary/sonic-horn) are generally not effective inside the furnace itself (molten slag is too well-bonded for acoustic energy to dislodge) but are effective immediately downstream where deposits are still partly dry. Furnace cleaning is dominated by steam [sootblowers](/glossary/steam-sootblower) and water cannons.

## Related terms

- [Boiler](/glossary/boiler)
- [Waterwall](/glossary/waterwall)
- [Slagging](/glossary/slagging)
- [Water cannon](/glossary/water-cannon)