Are Boiler Stack Economizers Worthwhile on Hot Water Boilers?

Boiler stack economizers boost the efficiency of hot water boilers.

Boiler stack economizers, or economizers for short, improve hot water boiler efficiency. The devices capture heat from the flue gases or exhaust, then recycle that heat, adding it to the feed water. Economizers are often added to boilers or built into the boiler design.

Benefit

Raising the temperature of the boiler feed water by 10 degrees Fahrenheit improves boiler efficiency by about 1 percent. According to "Practical Guide to Industrial Boiler Systems" by Ralph Vandagriff, "in terms of efficiency, the increase is 5-6 percent." Less energy is then required by the hot water boiler.

Savings

If assuming 5 percent energy savings, multiply the current annual cost to run the hot water boiler by 0.05 to determine the savings in energy costs. If a hot water boiler costs $20,000 to operate per year, the savings are 0.05, multiplied by 20,000 for $1,000. If assuming 6 percent energy savings, multiply the $20,000 annual cost to run the hot water boiler by 0.06 for $1,200 saved.

Cost-Benefit Analysis

Determine the cost of the boiler stack economizer. Add the cost of installation to the equipment's cost for a total. Divide the total cost by the saved energy costs. The result is the number of years required to repay the cost of installing an economizer. If a new economizer costs $10,000, that cost divided by $1,200 of annual savings gives an 8.33 year pay back period.

References

• "Steam and Hot Water Primer"; Chris Langley, Andrew Sacks; 2009
• "Boiler Control Systems Engineering, Second Edition"; G.F. (Jerry) Gilman; 2010
• "Practical Guide to Industrial Boiler Systems"; Ralph Vandagriff; 2001
• "Commercial Energy Auditing Reference Handbook"; Steve Doty; 2010
• "2006 National Plumbing & Hvac Estimator"; James A. Thompson; 2005

Resources

• "Boilers for Power and Process"; Kumar Rayaprolu; 2009
• "Industrial Boilers and Heat Recovery Steam Generators"; V. Ganapathy; 2002