Every winter, the same question arises: what is the most efficient fuel source for my heating needs? Typically, the consumer has five choices: Gas (Natural or Propane), Oil, Electricity, Solid Fuels, or Renewable Energy. Fossil fuels come in different forms and have an energy content per unit fuel that in the US is measured in British Thermal Units (BTUs). Elsewhere, kilowatts (kW) are the preferred measuring unit. The conversion factor is 3.46 BTU/W.

Natural Gas and Propane

Natural gas is currently the primary means by which most people heat their homes in the United States and most of Europe. Usually, it is the most convenient fuel source in urban areas and hence very popular... The homeowner has little more to do but pay the bills to keep the gas flowing. Natural Gas is usually transported in gaseous form through pipelines or via tanker trucks or ships in liquid form.

Natural gas is supposed to be made up principally of methane, though other gases can and do sneak into the mix. Whenever the local gas utility is running low on its principal fuel, substitutions can, and will, be made. Natural gas has an energy content of about 100kBTU per therm or 103kBTU per ccf (100 cubic feet). However, anecdotal evidence suggests that the actual heating value of "Natural Gas" coming out of the distribution pipe may vary from as little as 60kBTU up to 160kBTU per ccf.

Propane is derived from petroleum products during the refining process. It is transported in pressurized containers and the gas containers that the propane is stored in are frequently found adjacent to homes in rural areas where there are no "Natural Gas" distribution networks. Perhaps unsurprisingly, the distributors of Propane do not use the same units of measure as the "Natural Gas" competitors. Thus, Propane quantities are measured in gallons, not ccf, and it contains 91kBTU per gallon. Typically, Propane is a more expensive fuel source than natural gas on a $ per BTU basis.

Both Natural Gas and Propane integrate very easily and inexpensively into the forced-air heating systems which dominate the US market. Modern boiler systems that predominate elsewhere can also take full advantage of the ease with which these gases can be metered. So-called low-mass, modulating, and condensing boilers represent the pinnacle of energy efficiency and there are far more to choose from on the gas side of the business than the oil side in the USA.

That said, the gas companies could do a better job of not giving their potential customers the wrong illusion that gas appliances require less maintenance than oil-fired ones, or that gas is cheaper to heat with than heating oil. Until you compare historical vs. present-day price averages and compare on a $/BTU basis, you simply won't know. All heating appliances benefit from yearly maintenance, it keeps them running at peak efficiency and hopefully will uncover any issues before they leave you in the cold.

Heating Oil

Heating oil is a fuel most commonly found in the Northeast of the USA and it also still competes with its gaseous competitors in many other areas of the world. Historically speaking, home fuel oil replaced coal in many parts of the world as soon as it became widely available because it was a more convenient fuel - no ashes to deal with, less dust, etc. Hence, it is still possible to find ancient boilers or furnaces in basements that were converted from coal to Heating Oil and perhaps even to Gas.

Home Heating Fuel is also known as #2 fuel oil and is very similar to Diesel fuel used in transportation. It has an energy content of about 139kBTU per gallon. Because oil requires more sophisticated burner systems than gas does to be fired efficiently, oil-fired heating appliances typically cost more than their gas-fired competitors. However, heating fuel is somewhat safer to store than gas since it's much harder to ignite. On the other hand, a leak in your tank can end up costing a lot of money to fix.

Electricity

Believe it or not, many industry pundits in the 1950's thought that atomic energy would make electricity too cheap to meter. Nowadays, electricity costs are rising quickly in line with other fuel sources such as natural gas (because natural gas is becoming the primary fuel source for many new electrical generation facilities). However, if you happen to live close to a subsized electrical source such as a hydro-electric dam, your electrical costs may be very, very low. Electricity has a heating value of about 3.4kBTU per kWh.

Electricity can be used to run a variety of heating and cooling appliances, ranging from simple resistance heaters to air conditioners and heat pumps. The most efficient heat pumps usually use the ground as a heat exchanger and achieve efficiencies in excess of 400% under the right conditions.

Solid Fuels

Solid fuels were the only active means of heating a home before the discovery of heating oil. Whenever other fossil fuel prices rise, the interest in either wood heat or coal rises as well. Granted, there are vast supplies of coal in the US and we won't be running out of them anytime soon. On the other hand, there is a reason that people stampeded towards the use of other fuel sources: convenience. Coal or wood-based heating systems need a lot more attention and care than people typically have time for. I would treat the performance claims of many wood boiler manufacturers with healthy suspicion and visit people who have actually operate such boiler systems to see what their experiences were. Boilers that burn wood with a gasification step are probably tops for efficiency.

Renewable Energy Sources

Solar heating has been used for centuries, yet it's last great adoption spurt was after the last energy crisis in the 1970's prompted government subsidies. The tax credits meant well but ultimately gave much of the industry a bad name because many systems were installed improperly, had serious design defects, etc. as can be reviewed in the excellent "Lessons Learned" tome from ECS Solar.

However, much of the industry collapsed and then matured a great deal after the tax subsidies were ended by Ronald Reagan. Nowadays, you can buy a wide variety of solar water heaters, solar cell systems, wind generators, etc. that have a proven track record (and modest tax breaks as well). Renewables make a lot of sense for homes that have been built in remote locations because getting energy to them is usually very expensive.

Usually, solar hot water systems are the easiest to justify, particularly if you live in a area that gets a lot of sun. Similarly, photovoltaic systems can do a great job of generating peak electrical power just as the power needs of utilities, etc. peak as well (due to air conditioning).

Here are some neat resources on the web to peruse:

• EERE guide to calculating payback rates for investements.
• Consumer Energy Council of America guide to oil vs. gas.
• If you live in Massachusetts and use heating oil, I highly recommend becoming a member of the Mass Energy Consumer Alliance. They have a frequently-updated page with information on oil-price trends.

Choose your heating and cooling systems wisely and try to get as much information about the different fuel choices you have before committing to a contract. For example, the very high efficiencies of ground source heat pumps sound very attractive until you examine the enormous up-front costs that these systems usually carry. Plus, the fuel that powers a ground-source fuel pump (electricity) has to come from somewhere...

After long reflection, we went with oil heat in our home. Burning coal or wood in a densely-populated area is a no-go. While we have access to Natural Gas, the local gas prices are so sky-high that even if we account for fuel efficiency differences between a condensing gas boiler and the non-condensing oil boiler we ultimately chose, that oil still comes out less expensive than gas. Way to go Nstar!

The way to calculate for yourself which fuel source makes the most sense, start by bringing all the fuels to a consistent unit of measurement. It's probably easiest to use kWh since our electric bills are already metered in that unit. Simply call around and get the current prices for the fuels you'd like to consider. Now convert the many different fuel prices into comparable measures:

Please note that the above prices are fictional. However, you can download my Fuel Price Comparison Spreadsheet and fill in your own fuel cost values. If you want to be more accurate, also account for the efficiency of the heating system you're using. Modern heating systems that use fossil fuels can mbe 95%+ efficient, while ground source heat pumps can be 400%+ efficient.

Ultimately, the best way to reduce your fuel bill is to ensure that your heating/cooling plants operate at peak efficiency and that you've done everything you can to increase the thermal performance of your home. That means insulating, weatherizing, and taking advantage of simple devices like the GFX Heat Exchanger to flush fewer BTUs down the drain, or to mount a desuperator on a air conditioning condenser to increase its efficiency and heat domestic hot water at the same time.