|Fig. 1: Heating Fuel Consumption  (Courtesy of the EIA.)|
According to the U.S. Department of Energy, the primary consumption of all energy use in households is attributed to space heating.  As the largest residential use of energy and the most expensive use, there is a financial and energy benefit to evaluating the current use of energy for household heating. The external component to the efficiency of a home heating system is the thermal envelop which includes the walls, roof, insulation, windows, weather stripping, and any other parts of the building that separate the living space from the outdoors.  The internal components include the fuel type used for heating and the system type. Some conclusions can be identified from comparing heating fuels and heating systems. Are the most widely used systems the most efficient? Are the most widely used fuels the least expensive? A survey of home heating fuels and systems will reveal the efficiencies and expenses of the different systems.
The nine primary heating fuels in the U.S. are fuel oil, electricity, natural gas propane, wood, pellets, corn, kerosene and coal. Of those fuels, natural gas and electricity are the dominate sources of space heating accounting for 85% (50% natural gas, 35% electricity) of households.  Electricity is becoming the more common form of heat for new homes, but natural gas has been the dominant heating fuel in the US for several decades. 
Each fuel can be evaluated and compared based upon fuel cost per amount of heat produced. Given the fuel price per unit and fuel heat content per unit, the cost per fuel heat content (BTU) can be calculated as:
|Price per Million BTU =||Fuel Price per Unit
Fuel Heat Content per Unit
The Fuel Cost Comparison report found natural gas to be the most cost effective at $6.20/ million BTU.  Although natural gas from a fuel cost perspective would be the best choice, the type of heating system utilized also contributes to determining the optimal form of home heating.
The heating system type accounts for the efficiency of heating a home and different type and ages create variations of efficiency. Older heating systems are typically less efficient than newer ones because the system is nearing the end of its life cycle. Another contributor of inefficiency is incorrect sizing of heating systems which leads to wasteful operation.  There are many types of heating systems used including heat pumps, solar heating, electric resistance heating, furnaces and boilers, wood, pellets, steam and hot water radiators, radiant heat, and portable heaters.
Furnaces and boilers are the most common form of heating in the US and are fueled by natural gas, fuel oil, coal or electricity.  Natural gas and electricity, as we discussed, are dominant and are measured by annual fuel utilization efficiency (AFUE), required by the Federal Trade Commission, which is the ratio of heat output compared to the total fuel consumed.  Although all electric furnaces and boilers have an AFUE of 95-100%, the cost of electricity makes them an uneconomical choice. On the other hand, the use of a natural gas furnace or boiler has an average AFUE of 80%, but the savings on fuel costs makes this a more affordable option. 
The high energy usage of space heating drives residential energy demand making it an essential component to address for energy consumption and efficiency. The high priority of heating energy consumption also makes it an important financial expense to the consumer. A life cycle analysis of the home heating system is important for home owners and property developers to consider when making an informed decision at the time of new construction or renovation which would influence efficiency and cost.  Although there has been an increase in high efficiency heating systems that use electricity; natural gas is the most cost effective because of its low fuel costs. 
© Lauren Jaramillo. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Annual Energy Review 2011," U.S. Energy Information Administration, DOE/EIA-0384(2011), September 2012.
 "Elements of an Energy-Efficient House," U.S. National Renewable Energy Laboratory, DOE/GO-10200-1070, July 2000.
 K. Hellevang and C. Pedersen, "Fuel Cost Comparison," North Dakota State University Extension, AE-1015, February 2012.
 V. P. Shaw, D. C. Debella and R. J. Ries, "Life Cycle Assessment of Residential Heating and Cooling Systems in Four Regions in the United States," Energy and Buildings 40, 503 (2008).