In the United States, the fuel used to heat homes depends largely on location, climate, and available infrastructure.
Regional Patterns:
- Northeast: Cold winters mean high heating needs. Many homes use heating oil or natural gas.
- Midwest & Mountain States: Natural gas and propane are common; some rural areas still use wood or coal.
- South: Milder winters (fewer "heating degree days"—a measure of how cold it is over time) mean less heating overall. Electricity is the dominant heating source here.
- West Coast: Mix of natural gas and electricity, with growing interest in heat pumps and renewable energy.
Looking Ahead: Electricity is the second-most used heating fuel nationwide—and its use is expected to grow. Many states are promoting "electrification" (switching from gas/oil to electric systems) to reduce carbon emissions.
Text description of the Share of Homes by Primary Space Heating Fuel and Census Region image.
The image is a map of the United States divided into four Census regions: West, Midwest, South, and Northeast. Each region features a pie chart representing the primary space heating fuels used in 2009. The pie charts are color-coded according to a legend on the right, showing different fuels: natural gas (yellow), electricity (blue), heating oil (brown), propane (green), wood (light-brown), and kerosene/other (gray). In the West, the pie chart shows a majority in electricity with natural gas as a significant portion. The Midwest chart is dominated by natural gas. The South has a large section for electricity with natural gas also significant. The Northeast shows a mix of heating oil, natural gas, and electricity. The lower right corner has a separate pie chart indicating the U.S. total, summarizing 110 million heated homes, showing a predominant use of natural gas and electricity.
Fuel Comparisons
| Fuel | Capacity | Consumption | Additional Information |
|---|---|---|---|
| Natural Gas | Measured in British thermal units per hour (BTU/h). Most heating appliances for home use have heating capacities of between 40,000 and 150,000 BTU/h. In the past, gas furnaces were often rated only on heat input; today the heat output is given. | Consumption of natural gas is measured in cubic feet (ft3). This is the amount that the gas meter registers and the amount that the gas utility records when a reading is taken. One cubic foot of natural gas contains about 1,000 BTU of energy. | Utility companies often bill customers for CCF (100 cu. ft) or therms of gas used: one therm equals 100,000 BTUs. Some companies also use a unit of MCF, which is equal to 1,000 cu. ft. One MCF equals 1,000,000 BTUs (1 MM BTUs). |
| Propane or Liquefied Petroleum Gas (LPG) | Measured according to BTU/h. | Consumption of propane is usually measured in gallons; propane has an energy content of about 91.300 BTUs per gallon. | Can be used in many of the same types of equipment as natural gas. It is stored as a liquid in a tank at the house, so it can be used anywhere, even in areas where natural gas hookups are not available. |
| Fuel Oil | The heating (bonnet) capacity of oil heating appliances is the steady-state heat output of the furnace, measured in BTU/h. Typical oil-fired central heating appliances sold for home use today have heating capacities of between 56,000 and 150,000 BTU/h. | Oil use is generally billed by the gallon. One gallon of #2 fuel oil contains about 140,000 BTU of potential heat energy. | Several grades of fuel oil are produced by the petroleum industry, but only #2 fuel oil is commonly used for home heating. |
| Electricity | The heating capacity of electric systems is usually expressed in kilowatts (kW); 1 kW equals 1,000 W. A kilowatt-hour (kWh) is the amount of electrical energy supplied by 1 kW of power over a 1-hour period. Electric systems come in a wide range of capacities, generally from 10 kW to 50 kW. | Electricity is sold in kWh (kilowatts per hour). | The watt (W) is the basic unit of measurement of electric power. |
Heating Values of various fuels
Each unit of fuel when burned gives different amounts of energy. The energy that is released when a unit amount of fuel is burned is called the heating value. The heating value of a fuel is determined under a standard set of conditions. A comparison of approximate heating values of various fuels is shown in the table below.
| Fuel | Unit | Heating Value (BTU's) |
|---|---|---|
| Natural Gas | CCF (100 Cu. ft) or Therm | 100,000 |
| Natural Gas | MCF (1,000 Cu.ft) | 1,000,000 |
| Fuel Oil | Gallon | 140,000 |
| Electricity | kWh | 3,412 |
| Propane | Gallon | 91,300 |
| Bituminous Coal | Ton | 23,000,000 |
| Anthracite Coal | Ton | 26,000,000 |
| Hardwood | Cord | 24,000,000 |
Just as we saw back in Lesson 2, all energy conversion devices are not 100% effect. In most heating systems, we have some sort of furnace or boiler to burn our fuel. This process is not perfectly efficient.
Annual Fuel Utilization Efficiency (AFUE)
What Is AFUE?
AFUE (Annual Fuel Utilization Efficiency) is a rating that tells you how efficiently a furnace or boiler converts fuel into usable heat over an entire heating season.
Simple Definition:
AFUE = (Heat Output ÷ Fuel Input) × 100%
Think of it like a report card for your heating system—the higher the score, the better it performs!
How to Read AFUE Ratings
| AFUE Rating | What It Means | Example |
|---|---|---|
| 90% | 90% of fuel becomes heat; 10% is lost | For every $100 spent on fuel, $90 heats your home, $10 goes up the chimney |
| 80% | 80% efficient; 20% wasted | Older systems often fall in this range |
| 98% | Nearly all fuel is used for heating | Top-tier modern ENERGY STAR models |
What AFUE Does (and Doesn't) Measure
AFUE Measures:
- Efficiency of the furnace or boiler itself
- How well the unit converts fuel to heat at the source
- Performance under standardized testing conditions
AFUE Does NOT Measure:
- Heat loss through ductwork (leaky ducts can waste 20–30% of heated air)
- Poor insulation or air leaks in your home
- Thermostat settings or user behavior
- Distribution losses from pipes (in boiler systems)
Important: A 95% AFUE furnace can still heat your home inefficiently if your ducts are leaky or your attic isn't insulated!