What is the efficiency of domestic heating boilers, how it is calculated and on what depends

Domestic heating boilers are essential to keeping our homes warm and comfortable. Our heating systems’ central components, these appliances give us the necessary warmth in the winter. However, have you ever considered their level of efficiency? It’s critical to comprehend domestic heating boiler efficiency if you want to maximize energy use and cut expenses. Let’s examine the formula for calculating this efficiency and the variables that affect it.

When we talk about heating boiler efficiency, we’re talking about how well they turn fuel into heat for your house. In essence, it is a measurement of the percentage of energy input that is transformed into usable heat output. Comparing the amount of energy input, which is typically measured in fuel consumption, to the amount of useful heat output, which is typically measured in kilowatts or British thermal units, is how boiler efficiency is calculated. The percentage that results indicates how effectively the boiler is turning fuel into heat.

The effectiveness of residential heating boilers is influenced by various factors. First and foremost, the kind of fuel utilized is important. Different fuels, such as electricity, propane, oil, or natural gas, have different energy contents and combustion characteristics that affect how well they can produce heat. Furthermore, the boiler’s own technology and design are important. Because they can recover heat from exhaust gases, modern condensing boilers, for instance, are renowned for their high efficiency.

The boiler’s upkeep and state are also important factors. Boilers are susceptible to wear and tear, malfunctions, and deposit buildup over time, all of which can reduce their efficiency. To guarantee optimum performance and efficiency, routine cleaning, maintenance, and timely repairs are necessary. Furthermore, it’s crucial to size and install the boiler correctly. An boiler that is either too big or too small might not function well, wasting energy and raising utility costs.

Homeowners can make well-informed decisions about their heating systems by being aware of the efficiency of domestic heating boilers. Homeowners can maximize comfort while minimizing energy costs and environmental impact by selecting high-efficiency boilers, putting good maintenance practices into place, and taking into account variables like fuel type and size. In the end, increasing boiler efficiency helps the environment and our pocketbooks by lowering carbon emissions and fostering sustainability.

Factors Affecting Efficiency Calculation Method
The type of fuel used Efficiency = (Useful Heat Output / Total Heat Input) * 100%
The design and condition of the boiler Useful Heat Output = (Energy Released by Burning Fuel – Losses)
Insulation and maintenance Total Heat Input = Energy Content of Fuel

It’s important to comprehend how well home heating boilers convert fuel into usable heat for your home in order to appreciate their efficiency. The boiler’s efficiency is determined by dividing its heat output by its fuel consumption. To put it simply, you get more heat from the same amount of fuel when the efficiency percentage is higher. Boiler efficiency is affected by a number of factors, such as the fuel type used, the boiler’s size and design, the level of maintenance given to it, and even the climate in your home. You can lower energy expenses and increase the effectiveness of your home heating system by making the most of these variables.

Gross efficiency and net efficiency

Not all of the heat produced by burning fuel is used to heat the coolant; some of it is used for the boiler’s internal purposes, such as the turbine, circulation pump, fan or smoke pump, automation and electronic display, and electric drive (you already know that all energy sources are included in the calculation, including electricity if the boiler requires energy).

In light of this, the boiler efficiency is typically calculated by dividing the total heat produced (gross efficiency) by the total heat released (net efficiency).

This classification makes it possible to discern between the boiler’s level of technical perfection (gross efficiency) and its fuel and electricity consumption efficiency (net efficiency).

How to calculate the efficiency of the heating boiler

There are various methods for computing the values. The direct balance method, which involves determining the discrepancy between the outside air temperature and the actual temperature of the flue gases exiting the chimney, is the standard method used in European countries to determine the efficiency of a heating boiler. The equation is very easy to figure out:

Η br = 100% (Q1/Qi r), where

  • η br (read "this") – boiler efficiency "gross";
  • Q1 (MJ/kg) – the amount of heat that was accumulated, t.е. to use for home heating purposes.
  • Qi r (MJ/kg) – the total amount of heat released during fuel combustion;

Efficiency "gross" = (19/22)*100 = 86,3%, for instance, if Q1 = 19 MJ/kg and Qi r = 22 MJ/kg. Every measurement is done while the boiler is in its predetermined, standard operating mode.

Because the direct balance method does not account for the boiler unit’s heat losses, fuel underburning, operational deviations, and other peculiarities, the "reverse balance method," a fundamentally different and more accurate method of calculation, was developed. The formula that is applied is:

Η br is equal to 100 – (q2 + q3 + q4 + q5 + q6).

  • q2 – heat losses with flue gases;
  • q3 – heat losses due to chemical underburning of combustible gases (applicable to gas boilers);
  • q4 – heat energy losses due to mechanical underburning;
  • q5 – heat loss from external cooling (through the heat exchanger and the body);
  • q6 – heat losses with physical heat of slag removed from the furnace.

The heating boiler’s net efficiency as determined by the back balance method is:

Η br – Q s.н = η net, where

  • Qs.н – total heat and electric energy consumption for auxiliary needs in % expression.

The actual efficiency will nearly always differ from the manufacturer’s stated efficiency because it depends on various factors such as the quality of the power supply, smoke exhaust system, boiler and heating system installation, etc. The boiler’s stated efficiency and actual efficiency will differ from one another. д. On site, it has already been measured, accordingly.

What the thermal efficiency of boiler units depends on

The efficiency of heating boilers varies proportionally with the load; that is, as the heat load (amount of fuel burned) rises, so do the heat losses through the chimney or casing. To put it another way, operating at minimum output does not always guarantee full fuel combustion, which lowers efficiency.

For instance, the service manual for Protherm Wolf KSO gas boilers with capacities of 12.5 kW and 16.0 kW states that efficiency is 92.5% at maximum power (12.8 kW and 16.3 kW, respectively), but drops to 78.4% at minimum load (4.5 kW and 5.8 kW).

This is one of the key justifications for why selecting the boiler unit capacity requires careful consideration. For the majority of models, the best performance is obtained between 60 and 90 percent of the maximum capacity.

Otherwise, the efficiency is entirely dependent on the technological advancement of the model designed to lower the aforementioned q2-6 (temperature reduction in the flue gas, fuel combustion efficiency, burner modulation, thermal insulation, etc.), as well as the standard of boiler unit maintenance and operation. Over time, flushing, cleaning, and regular cleaning all have a significant impact on efficiency of the heating medium.

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Values of modern boilers depending on fuel type

Photo Type of boiler depending on the fuel burned Average efficiency, %
– Convection 87-94
– Condensing 104-116 *
Solid fuel
– Wood-fired 75-87
– Coal 80-88
– Pellet 80-92
– On diesel fuel 86-91
– On fuel oil 85-88
Electric heating elements 99-99,5

* From a physics perspective, the efficiency is limited to 100% since more heat energy can never be obtained than what is released during fuel combustion. But it all relies on your method of counting. Two meanings are available:

  • net calorific value – heat generated by the combustion of fuel when the products of combustion are simply removed through the chimney;
  • supreme heat of combustion – heat including energy contained in water vapor – one of the combustion products of combustible gases.

In addition, condensate produced from gas combustion products and deposited on an additional heat exchanger are stored thermal energy by gas condensing boilers. As a result, not all of the heat "flies down the chimney," and the flue gases’ temperature is nearly identical to that of the surrounding air.

The efficiency of heating boilers is determined by the lowest specific heat of combustion, as per current European and Russian norms; therefore, accounting for the additional heat extracted from the condensate yields values greater than 100%. Depending on the model and installation style, condensing gas boiler efficiency ranges from 96% to 98% when based on the reduced specific heat of combustion. Generally speaking, wall-mounted boilers have a higher efficiency than floor-standing boilers (this is true for all gas boilers).

The table also shows that the average efficiency of solid fuel boilers varies with the type of fuel used. This is because different fuels have different degrees of combustion, produce different amounts of heat, have different combustion temperatures, and lose heat when slag is physically removed from the furnace chamber. When using different kinds of fuel, even the same solid fuel boiler can operate with varying levels of efficiency.

In order to maximize energy efficiency and minimize expenses, homeowners must have a thorough understanding of domestic heating boiler efficiency. In essence, efficiency is a measurement of how well a boiler produces heat from fuel. Usually given as a percentage, this metric’s higher percentages denote greater efficiency.

The efficiency of a boiler is influenced by various factors. The boiler’s own technology and design are important factors. For instance, condensing boilers of today are renowned for being more efficient than those of the past. To ensure optimal performance, proper installation and maintenance are also necessary. Efficiency can be lowered by filthy filters, leaking ducts, or inadequate insulation.

A boiler’s efficiency is determined by dividing its total heat output by its fuel consumption. Usually, to do this, the boiler’s input and output are measured. The energy content of the fuel used serves as the input, and the heat the boiler produces serves as the output. The efficiency percentage can be calculated by multiplying the result by 100 and dividing the output by the input.

It’s crucial to remember that efficiency ratings given by manufacturers might not always accurately represent performance in real-world settings because they are based on ideal circumstances. Actual efficiency can be impacted by a variety of factors, including usage patterns, climate, and maintenance procedures. Over time, regular maintenance and tune-ups can help keep efficiency levels high.

In conclusion, homeowners trying to maximize energy use and cut expenses must take the efficiency of domestic heating boilers into account. When choosing, installing, and maintaining their heating systems, homeowners can make more informed decisions if they are aware of the factors that affect efficiency and how it is calculated. Homeowners can save money and support environmental sustainability by installing energy-saving measures and high-efficiency boilers.

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Sergey Ivanov

I like to help people create comfort and comfort in their homes. I share my experience and knowledge in articles so that you can make the right choice of a heating and insulation system for your home.

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