Maximize Condensing Boiler Efficiency

How Do Condensing Boilers Work?

Three condensing boilers that are installed side by sideBefore we cover condensing boiler efficiency, lets briefly discuss the basics of how they work. A condensing boiler is a water heating system designed to retrieve energy normally released from the boiler stack as waste. Once water vapor is created by the burning of gas in the boiler, it condenses back into a liquid and releases the dormant heat. This heat is then used to preheat the water entering the boiler, resulting in less fuel needed to bring the water up to temperature.

Latent heat is a significant source of energy. This means condensing boilers can potentially hold an efficiency rating of up to 98% in some cases. By comparison, a traditional boiler is generally between 70-85%. That means, on the low end, a condensing boiler is able to deliver an extra 10-15% efficiency rate.

How to Maintain Your Condensing Boiler for Optimal Efficiency

To keep your condensing boiler operating at peak performance, establishing a maintenance plan, and having a qualified technician conduct the maintenance is essential.

Below is a detailed maintenance plan to help ensure you’re addressing every element of your condensing boiler so that it can perform efficiently. As always, follow your manufacturer’s recommendations for routine maintenance and maintain a daily logbook.

For service techs performing maintenance, follow this annual start-up checklist:

  • Address reported problems.
  • Inspect the interior of the boiler.
  • Clean and vacuum if necessary.
  • Clean the condensate trap and fill it with fresh water.
  • Check for any water, gas, flue, or condensate leaks.
  • Verify flue and airlines are in good condition and sealed tight.
  • Check the system’s water pressure, system piping, and expansion tank.
  • Examine the fill water meter.
  • Test the boiler water.
  • Inspect the control settings.
  • Look over the ignition and flame sense electrodes.
  • Clean off any deposits and reposition.
  • Survey the wiring and connections.
  • Perform a start-up, checkout, and performance verification to ensure everything is in place.
  • Conduct a flame inspection.
  • Look over the flame signal. Note: The flame should be at least 10 micro amps at high fire.
  • Clean the heat exchanger if the flue temperature is more than 54°F (30°C) above the water return temperature.

If executing a combustion or performance test:

  • Clean the heat exchanger.
  • Remove and clean the burner using only compressed air.
  • Clean the blower wheel.

Important note: condensing boilers require return water temperatures below the dew point of the boiler exhaust. This is critically important for overall system efficiency. 

This checklist will help you ensure your condensing boiler efficiency is where it should be.

Heatmizer condensing economizer or flue gas heat recovery unit.

Not Ready For A Condensing Boiler?

If the idea of investing in a new boiler system is impractical, there are ways you can reach similar efficiency with a traditional boiler. This involves the installation of a condensing economizer or flue gas heat recovery unit.

These economizers work by reclaiming energy that would normally be lost in stack exhaust. In the same way a condensing boiler preheats feedwater, an economizers takes this captured energy and does the same thing.

“By recovering waste heat, an economizer can often reduce fuel requirements by 5% to 10% and pay for itself in less than 2 years.” – US Department of Energy


3D representation of a Heatmizer condensing economizer or flue gas heat recovery unit.

Learn more about how a Heatmizer economizer transfers waste heat from boiler exhaust gases and uses that energy to preheat the boiler feedwater. The overall effect is a decrease in fuel energy consumption for a given steam demand so you see maximum annual savings.

Have Questions About Condensing Boiler Efficiency?

Call the pro’s at Rasmussen Mechanical Services at 1-800-237-3141, reach out for a free estimate, email or chat with an agent. Our team is here to help!