---
title: "Waterwall"
description: "Waterwalls are panels of vertical evaporator tubes welded into a gas-tight membrane that line the furnace walls of an industrial boiler. They absorb the radiant heat of the burning fuel and produce most of the boiler's steam."
canonical_url: "https://sylio.co/glossary/waterwall"
last_updated: "2026-06-28T02:29:27.050Z"
---

**Waterwalls** are panels of vertical evaporator tubes welded into a gas-tight membrane that line the [furnace](/glossary/furnace) walls of an industrial boiler. They absorb the radiant heat of the burning fuel and produce most of the boiler's steam.

## Construction

Adjacent tubes are connected by a thin steel fin running their full length, forming a continuous gas-tight pressure boundary. Tube diameters are typically 38–63 mm, on 50–80 mm pitches. Wall sections can be hung from headers above (suspension waterwalls) or supported from below (sit-on).

## Fouling: slag, not ash

Furnace temperatures and radiant heat transfer mean that any ash that hits the waterwall is partly molten. Cooled rapidly against the tube wall, it solidifies as [slag](/glossary/slagging). Slag is hard, bonded, and grows in characteristic patterns: thicker near burner clusters, thinner in cold corners.

## Cleaning waterwalls

[Sonic horns](/glossary/sonic-horn) are not effective on hard furnace slag — the deposit is too well-bonded for acoustic energy to dislodge. The standard cleaning tools are:

- **Water cannons** — high-pressure water lances mounted on the waterwall, fired at specific tube sections
- **Wall blowers** — short retract sootblowers with multiple nozzles
- **Explosive deslagging** — periodic shock cleaning for severe build-up

## Tube failures on waterwalls

[Tube erosion](/glossary/tube-erosion-tube-wastage) and tube wastage on waterwalls are the leading cause of forced outages on coal-fired and biomass boilers. Mitigation is largely combustion-control rather than cleaning, but excessive aggressive cleaning (especially water cannons) contributes to thermal-fatigue cracking.

## Related terms

- [Boiler](/glossary/boiler)
- [Furnace](/glossary/furnace)
- [Slagging](/glossary/slagging)
- [Tube erosion / tube wastage](/glossary/tube-erosion-tube-wastage)
- [Water cannon](/glossary/water-cannon)