Is Boiler Energy Efficient ? 7+ Facts You Should Know


“Is Boiler Energy Efficient?”-this is the most common and obvious question before making a new purchase.

Though numerous factors affect the Boiler’s Efficiency, it is not a big deal to have a perfect understanding that help a buyer to have an assured and confident decision.

Which Boiler is Most Energy Efficient?

Electric Boilers are the most energy efficient. In most of the cases, electric boilers result in efficiency rates of 99% in comparison to 89 – 95% for most gas or oil boilers.

On the contrary to other boilers, electric boilers don’t require fossil fuels to burn to generate heat energy, what we put in the form of electricity we get output as the same. No loss of energy in the form of waste gases through chimneys, this results the high efficiency of electric boilers.

Water Tube Boiler; Image Credit: Wikipedia

What Type of Boiler is Energy Efficient?

At the time of purchasing a new steam system, boiler efficiency is the most common and frequently discussed criterion.

Different type of boilers have their own pros and cones and perform at different efficiency levels. Before purchasing a boiler we discuss about different factors but the most important one- is boiler energy efficient, because the original price of a boiler is a small part of expenses associated with it during its life time.

The costs of fuel is the major expenses related with a boiler, therefore smooth running and effective operation of the boiler is quite necessary to minimize the fuel costs. Thermal efficiencies, combustion efficiencies and heat losses through different causes are the determining factors of Boiler’s overall energy efficiency.

Is a Back Boiler Energy Efficient?

Though a back boiler is a type of very old conventional boiler system, now a days in comparison to other modern boilers back boilers are less energy efficient.

When we follow modern energy efficiency standards, one of the major drawback of Back Boilers is their low energy efficiency. A back boilers provide energy efficiency not more than 80% whereas modern combi boilers efficiency reach almost 100%.

Back Boiler is a type of heat exchanger used as room heater and for heating water, placed just beside an open fireplace or a domestic heating stove. Back Boilers get their name as they are fitted at the rear part of a burning chamber, hot water is delivered from the top of the chamber and cold water is fed at the bottom.

Old Back Boiler; Image Credit: Flickr

Is a Combi Boiler Energy Efficient?

Combi boiler is the most popular choice now a days as it offers lots of advantages, the prior one is energy efficiency, it can save money on your heating bills.

Combi or combination boiler is a combination of water heater and the central heating system inside a single unit. A combi boiler does not require any storage tank just like a conventional boiler as it provides hot water instantly.

is boiler energy efficient
Combination Boiler; Image Credit: Flickr

More affordable as it can be  installed easily  within few manhours. Parts are easily available in the market. Less space is required due to its compact size, clean water is supplied directly from the mains. Low pressure or air logs don’t make any issue as hot water is directly supplied from the mains.

How to Increase Boiler Efficiency?

Boiler heat loss is a serious concern as it leads to loss in the business.

All the heat losses(radiation and convection losses, blow down loss, stack loss, loss due to moisture content in fuel) cannot be fully recovered but can be controlled to a large amount thereby improving boiler efficiency which in turn save a lot of money. The occurring points of the heat losses must know to overcome them.

Technicians or boiler engineers follow few efficiency boosting steps which are listed below:

  • Combustion of fuel should be completed, so that no unburnt fuel is remained.
  • Re injection of unburnt fuel in the form of carbon into the furnace lead to complete combustion of fuel.
  • Ash remained at the bottom portion of the boiler is always at a high temperature with lot of sensible heat, use of this heat to preheat air or water in a boiler.
  • The fuel added to the boiler should always to be moisture free so that no heat is utilized to remove moisture from the fuel and all the heat is completely used in making steam from water.
  • Regular inspection and proper insulation of a boiler reduce the radiation and convection heat losses to the surrounding.
  • Calibrating the boiler at different firing level maintain just enough air supply for complete combustion of fuel which improve boiler efficiency.
  • An economizer heats the feed water using the wasted hot flue gases, so installation of an economizer is the priority of a steam boiler to enhance its efficiency. Economizers save fuel consumption as well as prevents the damages occurred due to feeding the boiler with cold water.
  • Maintain a low stack temperature.
  • Insulation of large valves of a boiler is necessary to reduce heat losses from these valves.
  • Condensing boilers are water heaters where gas or oil are used as fuels, high efficiency is obtained by condensing water vapor from exhaust gases, thereby recovering the latent heat of vaporization.

How to Improve Boiler Combustion Efficiency?

Combustion efficiency of boiler is improved with increasing additional or excessive air supply to completely burn the fuel.

Boiler combustion efficiency is the burner’s ability to burn fuel measured by unburned fuel quantity and excessive air in the exhaust. If the boiler is operated in a condition of optimum amount of excess air, it will minimize the heat loss up the stack and improve the combustion efficiency.

The stack temperature and concentrations of flue gas oxygen or CO2 are the basic indicators of combustion efiiciency.More the excessive air in the exhaust means less amount of unburned fuel in the same. In comparison to solid fuels, combustion efficiency is higher for fuels in the form of liquid and gases.

What Makes a Boiler Inefficient?

Factors that make aboiler inefficient are as follows:

Excessive Air Supply

Excessive air supply can improve combustion efficiency until the amount of  heat loss through excessive air is more than the heat generated by the highly efficient combustion.

Main problem associated with excessive air supply is that it absorbs a part of heat obtained from combustion and therefore a lesser amount of heat is supplied to water in the boiler.

Calibrating the boiler continuously at different firing level regularly may resolve this problem.

Flue Gas Temperature

Stack temperature or Flue Gas Temperature defines the temperature of the combustion gases at the time of leaving the boiler, the high stack temperature indicates the heat generated by the boiler is not effectively used to generate steam or the heat is being lost.

Installation of economizers and combustion air heaters are the only solution to recover heat.

Convection and Radiation Losses

Convection and Radiation losses are the energy losses in the form of heat emanating from the boiler. Complete elimination of these losses are not possible but can be reduced by installing high quality insulation and controlling the airflow over the boiler surface.

Ambient Air Temperature

Stack temperature and boiler efficiency are highly effected by the temperature of the ambient air. The temperature of combustible air at the entrance of the boiler is ambient temperature. An ambient temperature of 70-80 degree F is generally assumed by the manufacturers for the optimum boiler energy efficiency.

Steam Losses

Steam and hot water sometimes leaked through the leakage in piping as well as through steam traps which leads to energy losses. Regular inspection is necessary to avoid energy losses.

The influence of above factors decide “is boiler energy efficient?” Therefore the proper monitoring and control of these factors is quite necessary.

Why Boiler is not Energy Efficient?

There are several factors which result heat losses and impact the boiler energy efficiency. Excessive air supply, steam losses, convection and radiation losses, ambient air temperature, flue gas temperature are the major causes of boiler inefficiency.

Conclusion:

In this article we try to answer the question,” Is Boiler Energy Efficient?”. Before wrapping up the article we can say Electric Boilers are quite popular now a days for domestic uses due to its high energy efficiency. We can also prefer Combi or Combination Boilers as they also provide lots of advantages including high energy efficiency.

Sangeeta Das

I am Sangeeta Das. I have completed my Masters in Mechanical Engineering with specialization in I.C Engine and Automobiles. I have around ten years of experience encompassing industry and academia. My area of interest includes I.C. Engines, Aerodynamics and Fluid Mechanics. You can reach me at https://www.linkedin.com/in/sangeeta-das-57233a203/

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