---
title: "Hot-side ESP / cold-side ESP"
description: "Hot-side and cold-side describe where an electrostatic precipitator sits in the flue-gas path relative to the boiler air heater."
canonical_url: "https://sylio.co/glossary/hot-side-esp-cold-side-esp"
last_updated: "2026-06-28T02:29:30.933Z"
---

**Hot-side** and **cold-side** describe where an [electrostatic precipitator](/glossary/electrostatic-precipitator) sits in the flue-gas path relative to the boiler [air heater](/glossary/air-heater).

<table>
<thead>
  <tr>
    <th>
      Type
    </th>
    
    <th>
      Position
    </th>
    
    <th>
      Gas temperature
    </th>
    
    <th>
      Why used
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      Hot-side ESP
    </td>
    
    <td>
      Upstream of air heater
    </td>
    
    <td>
      300–400 °C
    </td>
    
    <td>
      Avoids high ash <a href="/glossary/resistivity">
        resistivity
      </a>
      
       that causes <a href="/glossary/back-corona">
        back-corona
      </a>
      
       on low-sulphur coals
    </td>
  </tr>
  
  <tr>
    <td>
      Cold-side ESP
    </td>
    
    <td>
      Downstream of air heater
    </td>
    
    <td>
      130–180 °C
    </td>
    
    <td>
      Lower capital cost; standard for medium- and high-sulphur fuels
    </td>
  </tr>
</tbody>
</table>

## Trade-offs

Hot-side ESPs handle larger gas volumes (lower density at high temperature) and need bigger shells. They were popular in the 1970s–80s for Western US sub-bituminous and lignite coals. Most new installations are cold-side, often combined with flue-gas conditioning to manage resistivity.

## Cleaning implications

Both designs benefit from acoustic cleaning. Hot-side ESPs need high-temperature horn materials such as [Inconel 625 or 718](/glossary/inconel-625-718); cold-side ESPs can use [316 stainless](/glossary/aisi-316-316l-stainless) but face cold-end corrosion risks if dew-point excursions occur.

## Related terms

- [Electrostatic precipitator](/glossary/electrostatic-precipitator)
- [Resistivity (fly-ash)](/glossary/resistivity)
- [Back-corona](/glossary/back-corona)
- [Air heater](/glossary/air-heater)