Heating efficiencies and greenhouse emissions


This page compares methods of home heating in terms of their relative efficiency, greenhouse gas emissions and other environmental aspects. Several methods of home heating are electrically powered, so this page also discusses the environmental implications of a number of electrical generation technologies.

This page was created August 2002, modified 2017/02/09
Contact: David K. Clarke – ©

  • Heating energy sources discussed include: electricity, coal, gas, firewood, and oil.
  • Methods of electrical generation discussed include: biogas, biomass, coal, nuclear, oil, gas, wind, solar heat, solar photovoltaic, and hot dry rock.
  • Electrical heating methods discussed include reverse cycle air conditioning (heat pump) and heat bank as well as the more obvious ones.
Always remember that warming a room requires much less energy than warming a whole house and warming a person within a room requires much less energy than warming the whole room.

I want to make this site as useful, informative, and correct as possible. If you believe I've missed an important home heating method here, or if you think I'm wrong on some point, I'd be very pleased to have your comments.


Major sections on this page are...

Heating: characteristics Table 1

Coal | Electricity | Firewood | Gas | Oil

Electricity generation: methods Table 2

Biogas | Biomass | Coal | Hot dry rock | Hydro | Nuclear | Oil | Solar photovoltaic | Solar thermal | Wind

Electrical heating: methods Table 3

Simple radiator | Oil filled convection heater | Fan heater | Heat bank | Reverse cycle air conditioner

General notes Table 4






This page uses several technical units. Energy units, definitions and conversions are available on an additional page.

Table 1

Various forms of home heating: greenhouse emissions, other pollution, efficiency, and sustainability compared

Also see energy cost calculator to help calculate the cost of your heating energy.
Fuel Greenhouse emissions Other pollution Efficiency Sustainability
Coal High; large production of CO2.

Coal is mainly carbon. Burning one tonne of carbon produces about 3.7 tonnes of carbon dioxide.
Smoke can be a problem, especially in cities. In an efficient stove, burning high quality coal and run correctly, there should be little smoke. Some coal contains sulphur and mercury, which produce toxic gasses when burned. The ash contains toxic substances that can leach into streams and groundwater. An open, old-style, fireplace is probably no more than 15% efficient, a well designed stove is 50% to 70%; possibly 80% when new. Not sustainable. Coal is a fossil fuel.
Fuel Greenhouse emissions Other pollution Efficiency Sustainability
Electricity Depends entirely on how the electricity is generated, see Table 2. No pollution where the electricity is consumed, but possibly major pollution where the electricity is generated. 100% or better in the home, but the inefficiency is in the electricity generation process. Methods of electrical heating are discussed in Table 3. Depends entirely on how the electricity is generated.
Fuel Greenhouse emissions Other pollution Efficiency Sustainability
Firewood Carbon dioxide is released, but so long as trees are planted at the same rate as they are burned there is no net increase in greenhouse carbon dioxide. Smoke can be a problem, especially in cities. In an efficient stove, burning dry wood and run correctly, there should be little smoke. Ash must be disposed of. Similarly to coal fired heating, an open, old-style, fireplace is probably no more than 15% efficient, a well designed stove is 50% to 70%; possibly 80% when new. Wood pellet burning heaters can also be highly efficient. Fully sustainable, so long as trees are planted at the same rate as they are burned. See also notes on gathering firewood.
Fuel Greenhouse emissions Other pollution Efficiency Sustainability
Gas Carbon dioxide in released. Moderate amounts if natural gas, large amounts if 'town gas'. Little pollution of consequence outside the house, but if burned in an un-flued stove they can release the highly toxic carbon monoxide and oxides of nitrogen inside the house. Non-flued types are 100% efficient in that all the heat is retained inside the house; flued types should be 50% to 70% efficient. Not sustainable. Gas is a fossil fuel, whether the gas is 'town gas' or natural gas.
Fuel Greenhouse emissions Other pollution Efficiency Sustainability
Oil Poor (better than coal, marginally worse than natural gas) Little air pollution, may be some SO2 depending on the oil. Around 50% to 70% if working well. Not sustainable, oil is a fossil fuel.

Table 2

Methods of generating electricity: greenhouse emissions, other pollution, efficiency, and sustainability compared.

Also see Pros and Cons of various electrical generation methods and Personal greenhouse impact calculator.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Biogas (from landfill) Collection of the methane seeping from landfill (buried rubbish) and burning it to generate electricity reduces greenhouse gas production. Carbon dioxide is released. None? Of all gas captured, about 60% is combustible methane.* One estimate is that 75% of the methane can be captured.* (Much of the remaining 25% is lost before sealing the landfill.) The collection of methane can continue so long as our society goes on burying organic waste.
* Cardiff University Internet site - WasteResearch
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Biomass Carbon dioxide is released, but so long as the biomass (bagasse, forestry waste, etc.) is replaced as fast as it is burned for electricity generation there is no net greenhouse gas production. Some smoke, smell? Probably low (15%?); would depend very much on moisture content. So long as the biomass is replaced at least at the same rate as it is burned, it is a sustainable source of electricity.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Coal fired Very poor, one of the world's greatest producers of CO2.

Coal is mainly carbon. Burning one tonne of carbon produces about 3.7 tonnes of carbon dioxide.

The SA EPA greenhouse intensity rating for black coal is 1.0, for comparison Victorian brown coal does worse at a rating of 1.2, that is, 1.2 times as much polluting CO2 is produced per kWh of electricity generated.
Can be poor. SO2, huge quantities of ash that must be disposed of. Sometimes heavy metals go up with the smoke. Modern, well designed coal-fired power stations with smoke scrubbers are much better than older types. Current best for brown coal in Australia is 28% (or 1220kg CO2/MWh of sent out electricity), and for black coal 37% (861kg CO2/MWh)*.
Combined cycle and cogeneration can greatly improve efficiency.
Not sustainable. Coal is a fossil fuel.
* Australian Greenhouse Office AGO.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Gas fired (natural gas) Poor, it produces large amounts of CO2, but better than coal or oil.

SA EPA greenhouse intensity rating is 0.6; combined cycle rates 0.4, and cogeneration does even better at 0.2-0.4.
Limited. Some SO2, depending on the feeder gas; this can be extracted. Combined cycle gas turbines have achieved 40% (or 451kg CO2/MWh) in Australia. Internationally, over 50% has been achieved.* Not sustainable. The world's supplies of natural gas are likely to run out before petroleum (and petroleum will run out long before coal).
* Australian Greenhouse Office AGO.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Hot dry rock No greenhouse emissions Minor pollution possible during the establishment stage; drilling very deep wells, etc. Non polluting during operation. I don't know. I don't think figures are available yet. This is a very new technology. The amount of suitable hot rock is finite, but very large; sufficient to provide all the world's electricity needs for several centuries, I believe.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Hydro No greenhouse emissions from the hydro-power stations themselves, but the reservoirs associated with the stations is another matter. CO2 and methane would be produced from flooded vegetation in the early stages, and also from vegetable matter that gets washed in and ferments. The flooding of valleys for hydroelectric dams causes loss of habitat and destruction of ecosystems. In some cases large numbers of people loose their homes. 60 to 85% for small systems, could be greater for heavy industrial installations.

(The Australian Snowy Mountains Authority was unable to give me a figure!)
High. Dams will eventually fill with silt; how long this may take will vary enormously depending on the location.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Nuclear No greenhouse emissions This is a very contentious point. Long-lived radioactive isotopes are produced. Permanent disposal of nuclear power station waste has not been successfully achieve anywhere (so far as I know), although the problems may be more political than technical. Production of plutonium, which terrorists may be able to steal and use in bombs, is of concern. Similar to other thermal electrical generation methods, eg. gas, oil. The amount of uranium in the earth is finite. Therefore its use in generating electricity is not sustainable. However, there is a huge amount of uranium that is minable. See the note on uranium, as a fuel, below.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Oil fired Poor, but produces more energy per kilogram of CO2 than does coal fired. Fair to poor. Variable quantities of SO2 depending on the oil used. Highest efficiencies in Australia are 34 to 37%, depending on the type of oil. Not sustainable. Oil is a fossil fuel.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Solar photovoltaic No greenhouse emissions in operation. There are some emissions in the manufacture of the panels. Non polluting in operation. Old panels must be disposed of at the end of their useful life; perhaps 20 years. Pollution in the manufacturing stage may be significant?

One less common, expensive, but highly efficient type of solar panel, gallium arsenide, contains toxins that need to be disposed of carefully at the end of the life of the panel.
From 10% to 34%; generally at the lower end of this scale in stationary electrical generation applications. Cells of greater than 15% tend to be expensive. 34% achieved only in laboratories. Power production is fully sustainable, manufacture and disposal may not be.
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Solar thermal None None Variable, depending on the method. Of little environmental importance. Fully sustainable
Type Greenhouse emissions Other pollution and problems Efficiency Sustainability
Wind No greenhouse emissions Visually wind farms can be a problem. They must be in windy places and this often means conspicuous places. They produce a fair amount of noise. Of little environmental importance Fully sustainable
See also cogeneration.

Table 3

Methods of home heating using electricity

Heater type Efficiency Comments
Simple radiator 100% The main advantage of a simple radiator is that it can be used to warm a person rather than to warm a whole room or house. To do this effectively it needs an efficient reflector and the person to be warmed must be in front of the heater.
Oil filled convection heater 100% Electrically heated elements within the oil warm the oil. Convection moves the warm oil to all parts of the heater. Then convection of the air around the heater and within the room warms the room.

The main disadvantage of this type of heater is that warm air rises; so the warmest air is that very close to the heater or close to the top of the room; see the illustration below this table.
Fan forced air heater 100% This contains heating elements and a fan. The fan blows air over the electrically heated elements, warming it, and then expels the air into the room.

Note that 'hot air rises', therefore the warm air blown out of this type of heater will rise toward the ceiling; however, this type of heater mixes the air more effectively than the oil filled convection type.
Heat bank 100% These use low tariff (off peak) electricity to heat a 'heat bank' with the heat being released into the room later, as required. Limitations are:
- The amount of heat that can be stored;
- The efficiency of the insulation. Heat will leak out at some rate even when it is not required in the room.
The heat bank may be magnesite bricks. Heating of the bank generally takes place over-night when electricity may be less expensive; the advantage in a heat-bank based heater is in cost, not in efficiency.
Reverse cycle air conditioner 100% to 400%* Also known as a heat pump. The principle is that of a refrigerator, ie. to move (pump) heat from a cooler place to a warmer place; in this case, to move heat from outside a house to inside. One of its limitations is that the outside section can become so covered with ice that it can no longer function.

*In effect greater than 100% 'efficiency' is achieved as more heat is brought into a house than the energy in the electricity 'consumed'. (The more correct term is Coefficient of Performance [COP] rather than efficiency.) Of course no process can produce more energy than it consumes, but heat pumps use a given amount of electricity to 'pump' a greater amount of heat from one place to another (this is explained in Wikipedia).

Heat map of room
Thanks to Australian Consumer's Association (Choice) for this illustration. It represents a room in cross section.

"This heat map of a test room clearly shows the stratification effect created by a convection heater when there's little air movement in the room: the yellow bar at the ceiling represents about 22°C, the purple bit (where your cold feet would be) about 14°C."

It is important to consider where the heat from a heater will go; warm air rises, cold air falls.

Note that all electrical heaters, in themselves, are at least 100% efficient in converting electricity into heat; although inefficiencies exist where the electricity is generated. See methods of generating electricity. It is not difficult to convert electical energy into heat. However, note that it is more effective to heat people within a house than to heat the whole house.

Of course, in most cases, heating a part of a house where there are no people, or heating a house when it contains no people, is energy wasted.

Table 4

General notes

Explanatory notes are here; shorter, definitive notes are in the glossary; also see the index

Biogas Organic matter confined in an environment with little oxygen (as in a landfill rubbish dump) will rot and produce methane gas. The methane can be collected and burned to generate electricity. Methane, generated by methods such as this, is called biogas.
Coal There are different types of coal ranging from lignite to anthracite. Lignite contains 60 to 75% carbon, anthracite 90 to 98%. Coals may also contain high percentages of water, which makes them less valuable as a fuel, especially if the water is saline.
  • The water must be removed before the coal can burn. If heat from burning the coal is used to 'boil off' the water, there is a corresponding decrease in the efficiency of the power station.
  • Sodium contained in salt can cause clogging in the combustion chamber.
Coal may also contain sulphur which becomes sulphur dioxide when burned. In turn, sulphur dioxide becomes sulphuric acid after reacting with water in the atmosphere; this is one of the chief causes of acid rain. Coal can also contain significant amounts of the toxic heavy metal mercury, which can be released into the atmosphere when the coal is burned.
Cogeneration Waste heat from industrial processes, or from thermal power stations, can be used for other purposes. In some cases more electricity may be generated, the heat could be used for community heating, or it might be used for desalination. Cogeneration can increase the effective efficiency of electrical generation from the typical 33% of fossil fuel power stations to 50 or even as high as 84%. (The 84%, or 314 kgCO2/MWh, has been achieved in Australia; from AGO).
Combined cycle An electrical power generation system where a flammable gas is burned to power a gas turbine and then the heat from the burned gas is used to produce steam which drives a steam turbine to generates more electricity. The flammable gas may be produced by the gasification of coal, or it may be natural gas, biogas, etc.
Efficiency The efficiency of a method of producing electricity is important when fossil fuels are being burned for energy because of the link between energy output and carbon dioxide output. The more efficient the method, the more energy per kilogram of carbon dioxide produced. However, efficiency of greenhouse friendly methods of producing electricity, eg. wind power, generally has no such connection to any form of pollution.

The efficiency of fossil fuel electrical generation methods can be expressed in two main ways:

  1. Efficiency of conversion of the heat of combustion into electricity;
  2. Electricity output per unit of carbon dioxide produced.
The latter method is used when greenhouse is the main concern.
Gathering firewood How the firewood is obtained is of great environmental importance. Cutting forest or scrub removes habitat, can increase the likelihood of flooding, and can cause loss of biodiversity. Even collecting dead wood removes habitat because many macro and micro organisms live in rotting wood. Cutting down old trees containing hollow limbs removes nesting sites for birds and 'homes' for other animals. You could also see my notes on firewood in its relationship to greenhouse, overpopulation, exercise, and environment.
Geosequestration As applied to the energy industry geosequestration is the deep burial of carbon dioxide. It is most talked about today as a potential means of stopping the carbon dioxide produced by fossil fuel fired power stations from entering the atmosphere. (Carbon dioxide is the major man-made greenhouse gas.) Geosequestration of carbon dioxide is entirely unproven on a commercial scale. Cost estimates vary around US$40 to US$60 per tonne (or US$50 to $100 per megawatt hour of electricity produced). Note that geosequestration does not destroy the carbon dioxide, it only removes it from the environment; hopefully, for a very long time.
Also see Sequestration and Geosequestration on my Greenhouse page.
Geothermal electricity This is generated by tapping naturally occurring steam from volcanic areas. In regard to greenhouse and other environmental concerns, it is very similar to hot dry rock.
Green electricity Many electricity retailing authorities offer 'green' electricity for sale. Consumer who buy green electricity pay a premium on the price for non-green electricity. For every kilowatt hour of green electricity that an electricity retailer sells, it is committed to buy a kilowatt from a an electrical generator that produces power by a greenhouse friendly method; that is, by a method that does not produce greenhouse gasses. It is also usual that these producers must not use any method that causes significant environmental damage of other types.
Heat bank home heaters These could theoretically be adapted to 'green' energy systems where the electricity is generated, and the heat bank heated, when the wind blows or when the sun shines. The heat could then be released into the home at some later time, when required. However, the sun often does not shine much at the time of year when home heating is required, and the wind may not blow for several days at a time. I suspect, therefore, that larger heat banks would be required than those found within the types of heaters contained within the living parts of homes. A suitable large capacity heat bank could be a water tank beneath the floor of the house.
Shale oil Shale oil is oil that can be extracted from shale by mining a shale that is saturated with oil and roasting it at about 500 degrees Celsius to extract the oil. The roasting process generally involves burning oil that has previously been extracted from the shale, so shale oil results in a very large net level of carbon dioxide release to the atmosphere. It is one of the most greenhouse polluting and least desirable forms of fossil fuel from an environmental point of view.
Smoke Smoke from coal and wood fires contains policyclic aromatic hydrocarbons (PAHs). These are carcinogens, and are very slow to be broken down by micro-organisms. While in the atmosphere they may be gradually broken down by ultraviolet light. You could also see my notes on firewood in its relationship to greenhouse, overpopulation, exercise, and environment.
Uranium as a fuel Current nuclear power stations can consume only the U235 isotope of uranium. This makes up only 0.7% of naturally occurring uranium; most of which is U238. It is possible to convert U238 into plutonium (Pu239) in what is called a fast breader reactor. This Pu can then be used to produce power in much the same way as U235. However, Pu can, if stolen, be used by terrorist to make nuclear bombs; so having many tonnes of Pu in many places around the world would be a hazard.
Proposed ' fast ' reactors, combined with a fuel reprocessing method that does not separate plutonium 239 from other transuranic elements and isotopes, can use most of natural uranium.


Short definitive notes are here, longer, explanatory notes, are in general notes

AGO Australian Greenhouse Office AGO
Bagasse Plant residue after the primary product has been extracted. For example, the grape mark remaining after the juice has been extracted for wine making, or the sugar cane pulp residue after crushing.
Biomass As used here, any matter of recent biological or organic origin. For example, forestry waste, bagasse, much of domestic refuse, garden waste.
Greenhouse intensity In the electricity generating industry this is the amount of carbon dioxide released into the atmosphere for each unit of electrical energy generated. For example, in combined cycle gas fired power stations the greenhouse intensity is typically around 0.4 Mt CO2/TWh (equivalent to 0.4 tonnes of CO2/MWh). Coal fired power stations do much worse at around 1 Mt CO2/TWh
CO2 Carbon dioxide is one of the main greenhouse gasses in the Earth's atmosphere. It is also the major cause for greenhouse warming. See also methane. Carbon dioxide has a much longer residence time in the atmosphere than does methane. Burning 1 tonne of carbon produces about 3.7 tonnes of carbon dioxide.
CO Carbon monoxide is an odourless gas that is highly toxic. It can be produced by partial combustion of carbonaceous material in an environment having insufficient oxygen for full combustion.
Fossil fuel A fuel that formed from the remains of plant and/or animal matter millions of years ago and has been mined from the earth. The rate of replenishment is virtually zero.
Isotope A form of a chemical element having a different atomic mass to other isotopes of that same element, but almost indentical chemical properties.
Magnesite A mineral composed of magnesium carbonate. As thermal capacity is generally greater in elements with lower atomic numbers, and magnesium, carbon, and oxygen have fairly low atomic numbers, one would expect the thermal capacity of magnesite to be quite high. It also can be heated to high temperature without damage.
Methane CH4. A highly flammable organic gas. Per kilogram methane is a much more effective greenhouse gas than is carbon dioxide. Methane has a shorter residence time in the atmosphere than does CO2.
Natural gas Piped or compressed natural gas (CNG) is a mixture mainly of methane and ethane. Liquified natural gas (LNG) is mainly propane, butane and probably pentane. All of these are fossil fuels which are drawn from wells.
NOxNitrogen oxides. A toxic gas, and one that is involved in acid rain.
Passive solar heating The heating of a home by maximizing the use of sunshine. Generally it is combined with appropriate insulation, some sort of passive heat storage medium and control of sunshine in summer.
Photovoltaic The direct conversion of light into electricity, using a 'solar panel'.
SA EPA South Australian Environmental Protection Authority
SO2 Sulphur dioxide. This gas is corrosive. If released into the atmosphere it eventually changes to sulphuric acid, the main cause of acid rain. This has lead to the wide-spread acidification of lakes and loss of forest.
Thermal capacity The amount of heat required to raise a unit mass of a substance by a unit of temperature. Put simply, the amount of heat that can be stored in something when it is heated.
Thermodynamics, first law The conservation of energy, which states that energy cannot be created or destroyed, but only converted from one form to another.
Thermodynamics, second law When energy is transformed from one form to another, it tends to flow from a higher grade or more ordered form - such as mechanical, electrical energy, chemical or high-temperature heat - to a lower-grade or more disordered form, ultimately low-temperature heat. So energy becomes degraded and less useful to humans. It is possible to reverse this natural flow, pushing low-grade energy 'uphill', but only by expending more high-grade energy at the input than is received at the output.
Town gas Also known as producer gas. A mixture mainly of CO and H, but also the nonflammable CO2 and N, produced in a process that involves the partial combustion of carbonaceous substances, usually coal, in an atmosphere of air and steam. It has a lower heating value than natural gas.



It is my intention to place common misconceptions about heating in this section. Suggestions welcome; contact: David K. Clarke.

Effect of a fan on electrical consumption

Some heaters have fans in them. Fans consume some electricity. Does this mean that if I use a fan heater I am getting less heat for the same amount of electricity?

Energy is, for all common purposes, indestructable (see the first law of thermodynamics). The little bit of electricity that goes to run the fan in a heater changes into heat after it has done its work (see the second law of thermodynamics). So you loose no heat.

Related pages

External site...

Reliant has a good Home Efficiency Improvement Guide. It gives 'Quick Fixes', 'Weekend Projects' and 'Appliances and Major Projects' to improve home energy efficiency.

Related pages on this site...

Climate change: an impending disaster of enormous proportions

The end of coal: the impending collapse of what has been a hugely profitable and harmful industry


Some energy units, definitions and conversions

Australia's Energy Future



I have gleaned information from many sources, most of which are listed in appropriate places in the text as links. I also obtained much useful information from the Clean Energy Future Report by the Clean Energy Future Group.