What Type Of Energy Is Least Efficient?
This article will examine why electric resistance heating is the least efficient form of heating a home. Electric resistance heaters work by passing electricity through resistive wires, which convert the electrical energy into heat. While simple and inexpensive, converting 100% of electrical energy into heat is incredibly wasteful compared to technologies like heat pumps which can move 3-4 times more thermal energy than the electrical energy they consume. We’ll look at the efficiency of common home heating systems like furnaces, heat pumps, and wood stoves to understand why using resistance heaters results in higher energy bills and greater environmental impact.
What is Electric Resistance Heating?
Electric resistance heating works by passing an electric current through a heating element, typically made of metal or another conductive material like graphite. As the current passes through the heating element, it encounters resistance, which converts the electrical energy into heat energy according to Joule’s first law. This generated heat is then transferred to air or water to provide space heating or hot water.
Some common examples of electric resistance heating include baseboard heaters, wall heaters, and electric furnaces. These all use heating elements made of Nichrome wire or some other metal alloy that offers high resistance. The higher the resistance, the more heat is produced as current passes through the heating element. This makes electric resistance heating a straightforward way to convert electricity into heat.
According to this overview, electric resistance heating is 100% energy efficient when viewed from a thermodynamic perspective, as nearly all the electrical energy is converted to heat.
Efficiency of Electric Heaters
Electric resistance heaters are unique in that they convert 100% of the incoming electric energy into heat (1). This makes them 100% efficient at converting electricity into heat energy. However, most electricity is produced at power plants by burning fossil fuels, which involves substantial energy losses. Only about 30-40% of the energy content in fuel at a power plant reaches customers as electricity (2).
When looking at overall system efficiency from primary fuel to delivered heat, electric resistance heaters are far less efficient than gas or oil heating which convert 90% or more of the fuel’s energy content directly into heat. This is why electric heating is generally the least efficient type of heating (1).
In summary, electric heaters themselves are 100% efficient at converting electricity into heat. But they rely on electricity that was produced inefficiently. Overall system efficiency of electric heating is low compared to direct use of gas, propane, or oil for heating.
Other Heating Methods
While electric heaters are common, there are several other types of heating systems used to warm homes, each with their own advantages and disadvantages:
Furnaces heat air which is blown through ductwork into different rooms. Gas furnaces tend to be more energy efficient than electric ones. According to Energy.gov, gas furnaces can reach AFUE ratings of 98%, while even the best electric furnaces top out around 95%.
Heat pumps move heat between indoors and outdoors instead of converting fuel directly into heat. They can provide heat in winter and cooling in summer. There are air-source heat pumps and more efficient ground-source heat pumps. Heat pumps run on electricity but are generally more efficient than electric resistance heating.
Boilers heat water which is circulated through radiators or pipes in the floor to heat a building. They commonly run on natural gas, propane, or fuel oil. According to Energy.gov, the best high-efficiency gas boilers can reach AFUE ratings over 90%.
Wood stoves burn wood or pellets to generate heat. Their efficiency can vary greatly depending on factors like insulation and stove design. Advanced wood stoves with catalytic combustors can approach efficiencies of 90%, while older stoves may be 50-60% efficient according to EPA.gov.
Efficiency of Furnaces
Furnaces are one of the most common heating systems for homes in North America. The efficiency of furnaces is measured by AFUE (Annual Fuel Utilization Efficiency). This measures the percentage of fuel that is converted into heat over the course of a typical year.
Modern furnaces range in AFUE from 80% to 98%. According to the U.S. Department of Energy, the minimum allowed AFUE rating for new furnaces is 78%. However, most models on the market today are at least 80% efficient at converting fuel into heat. High-efficiency furnaces can achieve ratings over 90% AFUE.
Higher efficiency furnaces waste less energy and can reduce heating costs compared to older, less efficient models. However, they also have a higher upfront cost. 80% AFUE models are considered the minimum standard, while 90%+ AFUE models are considered high-efficiency.
Efficiency of Heat Pumps
Heat pumps are one of the most energy efficient heating and cooling systems available today. Unlike traditional heating systems that generate heat through the combustion of fossil fuels, heat pumps simply move existing heat between indoor and outdoor spaces. This allows them to provide far more heating energy than the electrical energy they consume (1).
Heat pump efficiency is measured by the coefficient of performance (COP). This is a ratio of the heating or cooling provided vs. the electrical energy consumed. Most air-source heat pumps have a COP of 2-4. This means for every 1 unit of electricity used to power the heat pump, 2-4 units of heating or cooling are supplied to your home. The highest efficiency air-source heat pumps now exceed a COP of 5 (2).
Ground source heat pumps are even more efficient with COPs typically ranging from 3-5. The pipes buried underground can leverage more stable temperatures, allowing ground source heat pumps to maintain high efficiency even in very cold weather (3).
Overall, heat pumps are much more efficient than electric resistance heating where 1 unit of electricity equals 1 unit of heat. By leveraging refrigeration technology to move existing heat, heat pumps can be 200-300% more efficient.
Efficiency of Wood Stoves
Wood stoves have become much more efficient over the years. According to the EPA, old uncertified wood stoves were only about 50-60% efficient at converting the energy in wood into usable heat. However, newer EPA-certified wood stoves are 70-80% efficient on average.
The higher efficiency is achieved through better insulation, secondary combustion chambers, and tighter manufacturing tolerances. As hot exhaust gases are released from burning wood, modern stoves route them back through the firebox for more complete combustion before being vented outside. This extracts more heat while also reducing air pollution.
So while not quite as efficient as the best furnaces or heat pumps, new wood stoves convert over 3/4ths of the potential energy in firewood into usable heat. When using properly dried, seasoned firewood, they can be a relatively efficient heating option.
Why Electric Heating is Least Efficient
Electric resistance heating works by passing an electric current through a resistor, which converts the electrical energy into heat energy. This conversion process is 100% efficient, in that all of the electrical energy is converted to heat (source 1). However, most electricity is generated from fossil fuels, nuclear energy, or renewable sources that themselves are not fully efficient (source 2). This results in energy losses at the source of generation, making the overall process less efficient.
By contrast, other heating methods like furnaces and heat pumps utilize the chemical energy in natural gas or the phase change of refrigerants to produce heat. This allows them to generate more heat energy from the original fuel source than resistive heating, making them more efficient overall systems even if their combustion or refrigeration cycles are not 100% efficient (source 2). The key difference is that these technologies harness chemical and phase change processes rather than simple resistance to generate heat.
In summary, while electric resistance heating converts 100% of electrical energy into heat at the site of the heater, losses occur in generating the electricity in the first place. Meanwhile, technologies like furnaces and heat pumps utilize more efficient chemical and phase change processes to extract more heat energy from the original fuel.
Disadvantages of Electric Heating
Electric resistance heating has several drawbacks that make it one of the least efficient heating methods for homes. The main disadvantages are that electric heat is expensive to operate and not environmentally friendly.
Electricity prices have risen dramatically in recent years, making electric heating very costly compared to natural gas or other fuel types. According to the U.S. Energy Information Administration, electricity prices have increased over 30% in the last decade. This trajectory is expected to continue as demand rises and power generation and distribution infrastructure ages.
In addition, the conversion of electricity into heat is 100% efficient. This sounds positive at first, but it also means no heat is captured and reused as with condensing furnaces and heat pumps. The full electric input is lost as heat, wasting more energy overall compared to other systems.
Furthermore, electric resistance heating relies completely on the electrical grid. Unless the electricity is from renewable sources, electric heat has a large carbon footprint. Most U.S. electricity generation comes from fossil fuels like coal and natural gas. Using electric heating increases dependence on these resources that pollute the environment.
For these reasons, electric heating is the least efficient choice for home heating in terms of cost and environmental impact. Homeowners are often best served by high-efficiency gas furnaces, air source heat pumps, geothermal systems, or other alternatives.
Conclusion
In conclusion, electric resistance heating is the least efficient method for heating homes and buildings. Electric heaters work by converting 100% of electrical energy into heat, but they do not leverage any renewable energy sources or heat pumps to increase efficiency. Other heating systems like gas furnaces, heat pumps, and wood stoves are able to utilize combustion, movement of air, or renewable biomass to generate more heat per unit of fuel. While electric heaters provide a simple and low maintenance way to heat spaces, their efficiency is quite poor compared to other options. Homeowners concerned about energy costs should consider upgrading old electric furnaces and baseboards to more modern high-efficiency systems.
To recap, the intrinsic inefficiency of electric resistance heat makes it the least optimal choice from an energy standpoint. Alternative heating methods are readily available that can cut energy bills and carbon footprint dramatically. The high costs and wasted energy associated with electric heating demonstrate why it is the least efficient option for most homes and businesses.
