How to Check Gas Consumption of the Boiler

Posted 24th March, 2020

Before we find out ways to find out the gas consumption of the boiler, it is important to know a bit more about its functionality and efficiency. You need to check whether or not the installed boiler at your home is certified. There are benchmarks set by various authorities to measure factors such as efficiency, cost, and performance output.

Let's understand more about boiler efficiency and common methods used for calculations of gas consumption

The initial cost of a boiler is usually less than its time to time maintenance and other associated expenses. Quality boilers tend to consume less energy, demand less maintenance, and cost less than traditional boilers in the long run. It's essential to keep a regular check on the efficiency to get optimum performance. We are usually not concerned about the routine service and maintenance of our boilers, which leads to the increased cost of service later on. A gas boiler is a more economical choice for homeowners because it saves their higher monthly fuel charges. When compared to an oil boiler, it has significantly lower installation costs and expenses.

What is Boiler Efficiency?

It is a combined outcome of all parts and components of a boiler. It has many subsystems or subparts whose performance directly affects the overall efficiency of the boiler. Some of them are

  • Combustion Efficiency
  • Thermal Efficiency

Other than these, there are few other losses which play a crucial role in determining the output of the boiler.

Combustion Efficiency

It indicates the burner’s ability to burn fuel efficiently. The less the burning of fuel, the better the efficiency. Two other key parameters that often determine the burner efficiency are unburnt fuel and excess oxygen levels within the exhaust.

Thermal Efficiency

The thermal efficiency of a boiler determines the effectiveness of the heat exchange of the boiler. It primarily transfers heat energy from fireside to water. It is adversely affected by scale formation in the boiler tubes.

The overall boiler efficiency depends on many other parameters other than combustion and thermal efficiencies. Other parameters like: ON-OFF losses, convection losses, blowdown losses, radiation losses, etc. Let's talk about the direct and indirect efficiencies of a boiler in detail.

Direct Efficiency

It is a quick method for boiler efficiency calculation. The percentage of total heat output vs heat input is calculated to establish boiler performance.

Direct Boiler Efficiency = Heat output / Heat Input X 100
Direct Boiler Efficiency = Q X (h2 – h1) / (q X GCV) X 100


Q = Qty of steam generated.
h2 = Enthalpy of steam at the output of the boiler.
h1 = Enthalpy of feed water
Heat Input = q X GCV
q = Fuel Qty
GCV = Gross calorific Value

You can also calculate it here

Indirect Efficiency

The indirect efficiency of a boiler can be calculated by figuring out losses taking place in a boiler and then deducting the sum from 100%. Some of the factors considered for indirect efficiency include stack losses, radiation losses, blowdown losses, etc.

Boiler indirect Efficiency = 100 – (i +ii + iii + iv + v + vi + vii)


i) Dry flue gas
ii) Evaporation of water formed due to H2 in fuel
iii) Evaporation of moisture in the fuel
iv) Moisture present in combustion air
v) Unburnt fuel in fly ash
vi) Unburnt fuel in bottom ash
vii) Radiation and other unaccounted losses

*All quantities are percentage heat loss

This method for calculating efficiency generally involves checking the impact of all the losses which are measurable and are taking place in a boiler.

Now that we know about boiler efficiency and various ways to calculate it, it is also crucial to opt for certified boilers to save added costs during its operational life. Pay attention to these factors and save yourself from extra costs. This will save your hard-earned money and also let you contribute towards the environment.


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