Pressurised Deaerator v Hotwell Tank: Which is the better choice?

Published: 22nd July 2026 | Issue 106 Share article:

A pressurised deaerator and an atmospheric hotwell tank both pre-heat boiler feedwater and reduce dissolved oxygen before it enters the boiler. However, they differ significantly in oxygen removal performance, operating efficiency, and long-term cost.

The key difference is how dissolved oxygen is removed. A pressurised deaerator uses mechanical deaeration, typically reducing dissolved oxygen levels to below 0.02 ppm. Operating above atmospheric pressure, it heats feedwater to its saturation temperature, where dissolved gases become highly insoluble. Steam then scrubs the water, stripping out oxygen and other non-condensable gases before they are safely vented. This process provides excellent protection against oxygen corrosion while greatly reducing the need for chemical oxygen scavengers.

By contrast, a hotwell tank operates at atmospheric pressure, limiting water temperature to around 100°C. Because it cannot achieve the higher saturation temperatures of a pressurised deaerator, oxygen removal is far less effective. Heating alone removes only part of the dissolved oxygen, leaving higher residual levels and increasing reliance on chemical treatment to prevent corrosion.

A further advantage of a pressurised deaerator is its ability to maintain feedwater at approximately 105–107°C. Delivering consistently hot feedwater reduces the temperature difference between the boiler and incoming water, minimising thermal stress, improving boiler efficiency, and helping extend equipment life.

Hotwell tanks typically operate between 70°C and 85°C. When large volumes of cold make-up water are introduced, feedwater temperature can fall rapidly, increasing the risk of thermal shock and placing additional stress on boiler tubes. Over time, this can lead to higher maintenance costs and reduced equipment life.

Although a pressurised deaerator requires a higher initial investment, it offers a lower total cost of ownership through reduced chemical consumption, improved energy efficiency, and superior corrosion protection. Lower maintenance requirements, reduced unplanned downtime, and extended boiler life often provide a strong return on investment, particularly in larger or high-pressure steam systems.

Atmospheric hotwell tanks remain a practical and economical solution for smaller, lower-pressure applications. However, for demanding industrial operations where efficiency, reliability, and asset protection are priorities, a pressurised deaerator is generally the preferred choice.

All STL Power & Process Controls pressurised deaerators are proudly engineered, fabricated, and assembled in England. Manufacturing entirely within the UK provides complete oversight of every stage of production. Every system is manufactured to

PD5500 Category 3 or higher, ensuring high build quality, recognised design compliance, rigorous quality control, and dependable lead times.

To discuss your deaerator enquiries, please contact Julian@stlpowerprocess.com

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