The Three Boiler Efficiency Factors

When boiler efficiency is discussed one can mean three different things. This often times can be very confusing to those who do not truly understand boiler efficiency. Boiler efficiency actually comprises of:

• Combustion Efficiency
• Steady-State Efficiency
• Seasonal Efficiency 

To determine true boiler efficiency we must examine all three efficiency factors mentioned above. One of the factors can be determined to be very efficient but if we fail to look at the other factors we can miss another efficiency factor suffering big loss. It is thereby possible to determine that the boiler is very efficient in one aspect but very inefficient in another aspect. It is necessary to look at all three factors (and then some (mentioned below)) before declaring or determining the boiler to be efficient.

The Three Factors (Plus) of Boiler Efficiency Defined

• Combustion Efficiency - This is determined by examining how well the burners are burning the fuel during the combustion process.
• Steady-State Efficiency - This is determined by examining how well the boiler is utilizing the heat during the combustion process when the boiler is under full load conditions.
• Seasonal Efficiency - this is probably the most important factor because it is often very clear and it directly correlates to the final bill at the end of the heating season. It is a determination of how well the boilers used fuel over the entire heating season. This can be measured in actual energy costs, or, since the cost of fuels varies, the amount of actual fuel quantity used during the season. Seasonal Efficiency is often the most important to many building owners but if combustion efficiency or steady-state efficiency, one or both, is off then it can be reasonably assumed that the seasonal efficiency will suffer also. 

As with any technology there are methods we can employ to make improvements in individual components in the system and as a result make an improvement to the whole system. A technique used in diagnosing problems requires one to break complex systems down into small parts and observe their function. A person with good troubleshooting skills employs this method when solving problems whether they are simple problems or complex ones. A person who studies boilers can also use this method to define efficiency of the different parts of the boiler. For example:

• Thermal Efficiency of the heat exchanger inside the boiler - it has been proven that soot and/or scaling inside the heat exchanger will reduce the boilers efficiency. Simply put, soot and/or scaling inhibit the heat exchange process and can do so enough to reduce overall boiler efficiency.
• Loop Efficiency - this is applicable to all boiler systems including steam boilers. Once the steam or hot water leaves the boiler how much heat is lost in the loop and how does this heat loss affect the seasonal efficiency of the boiler. This is mainly applicable to the parts of the loop where usable heat is not necessary like sections of the loop which run in crawl spaces or in plenums and attics. Are these sections of piping sufficiently insulated? Have they been inspected for heat loss? The usable heat section of the piping can also be examined depending on the heat exchanger type. Simple fin and tube design in long straight runs can suffer from Laminar Flow issues. This will definitely reduce efficiency unless it is rectified. 

So one who is truly interested in boiler efficiency can find different areas where improvements can be made to the entire system. It requires dogged attention to the finer details by a qualified boiler technician. A good boiler technician like that can pay for themselves in annual energy savings and a properly maintained boiler which equals a more reliable boiler.

Here is a video of a boiler tripping on high limit and the pressure relief valve opening. This could possibly be the result of poor boiler maintenance or a malfunctioning component.

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