Boiler Efficiency

Unknown

Measuring the combustion gas composition and stack temperatures will give a fairly accurate estimate of steady state boiler efficiency. Depending on the amount of excess air supplied to the combustion process, the flue gas temperature will reflect the amount of heat absorbed by the boiler.

The lower the flue gas temperature, the higher the efficiency. For example, a gas boiler operating with 30% excess air and a stack temperature of 300F is operating at a steady state efficiency of about 83.5%. This calculation does not take into account the boiler jacket losses, and the reduction in efficiency due to cycling and standby losses which are encountered in real world operation, but at least it gives you a ballpark figure for comparison.

Justin Topel

How to tell?

I was wondering if there was an accurate way to approximate boiler efficiency. I think I remember some topics concerning stack temperatures, but is this always the case? If so, where can I find the charts at? I was just thinking about this when I go with our company to look at old systems. Is there a way that I could give them a realistic cost savings of replacement? Just because the tag says 80%, doesn't always mean that when they are very old. I know that there may be a way with an inline gas meter, fluid flow meter, and temp of water supply, but I was just trying to see if there was an easier yet fairly accurate method to figure this out.
Thanks

Mister T

Justin Topel

Charts?

Thanks for the response Mike. Where do I find the chart that explains the different stack temperatures or what is the formula? Another dumb question, what is excess air? How do I determine that parameter? I have no real experience with this except when I have helped in using a flue gas analyzer. Thanks again.

Mister T

Unknown

Justin

If you take a look around "The Combustion Zone", I`m sure you`ll find answers here.

Dave