---
title: "Attemperator / desuperheater"
description: "An attemperator (or desuperheater) sprays demineralised water into superheater or reheater steam to control outlet temperature. The water flashes to steam, lowers temperature by mixing, and is then re-superheated in subsequent tube banks. Attemperator action is the primary control loop for superheater outlet temperature."
canonical_url: "https://sylio.co/glossary/attemperator-desuperheater"
last_updated: "2026-06-28T02:29:25.483Z"
---

An **attemperator** (or **desuperheater**) sprays demineralised water into [superheater](/glossary/superheater) or [reheater](/glossary/reheater) steam to control outlet temperature. The water flashes to steam, lowers temperature by mixing, and is then re-superheated in subsequent tube banks. Attemperator action is the primary control loop for superheater outlet temperature.

## Why attemperation flow indicates fouling

When a superheater is clean, the tubes absorb the designed amount of heat from flue gas and the attemperator removes a known amount of excess to hit the steam set-point. As fouling reduces heat absorption, the steam emerging from the superheater is cooler than designed, attemperator flow falls, and the operator sees the cooler steam as a process drift.

**Falling attemperation flow at constant load is one of the earliest signs of progressive superheater fouling.** Performance engineers track it as a leading indicator before [heat rate](/glossary/heat-rate) drift becomes obvious.

## Sonic-horn relevance

Restoring attemperation margin by [sonic-horn](/glossary/sonic-horn) cleaning of superheaters and reheaters is a frequently-quoted commissioning result: a unit with falling attemperation flow regains 5–15 °C of headroom within weeks of horn installation.

## Related terms

- [Boiler](/glossary/boiler)
- [Superheater](/glossary/superheater)
- [Reheater](/glossary/reheater)