Types of Systems
There are two basic types of home heating systems-those that require a flame to operate (i.e., combustion based), and those that do not. Most central systems presently installed create heat by combustion, just as they did almost 100 years ago. These systems use a furnace to burn a fossil fuel (such as oil, natural gas or propane) or in some instances, wood. More advanced, non-combustion systems operate by transferring or moving heat from one location to another.

Combustion-Based Systems
Until the last few years, combustion-based systems have been the preferred heating systems for home and business owners because of their moderate installation and operating costs and wide availability in the market place.

Heat Transfer Systems
Non-combustion or heat transfer systems include heat pumps and geothermal systems. Heat pumps operate by capturing heat from outdoor air and transferring it inside of a home or business. Geothermal systems capture and transfer heat from the earth. Nearly all heat transfer systems can be reversed, providing central cooling as well as heating. Some heat pumps and most geothermal systems also provide domestic hot water at low operating costs.

Heat Pumps
Beginning in the 1970s, air-source heat pumps came into common use. They have the advantage of no combustion, and thus no possibility of indoor pollutants like carbon monoxide. Heat pumps provide central air conditioning as well as heating. And they are installation-cost competitive with a central combustion furnace/central air conditioner combination.

Heat pumps operate by moving or transferring heat, rather than creating it. During the summer, a heat pump captures heat from inside a home or business and transfers it to the outdoor air through a condensing unit. During the winter, the process is reversed. Heat is captured from outdoor air, compressed, and released inside.

Depending on climate, air-source heat pumps (including their supplementary resistance heat) are about 1.5 to 3 times more efficient than resistance heating alone. Operating efficiency has improved since the 70s, making their operating cost generally competitive with combustion-based systems, depending on local fuel prices. With their outdoor unit subject to weathering, some maintenance should be expected.

Geothermal Systems
More recently, even more advanced and efficient heating and cooling systems have emerged using the geothermal process. Sometimes called geothermal or ground-source heat pumps, these systems move or transfer heat like the air-source heat pumps. However, they exchange heat with the earth rather than the outdoor air. Since earth temperature remains relatively constant throughout the year, geothermal systems operate more efficiently than air-source heat pumps and generally without the use of resistance heat. And because they are working from those constant earth temperatures, there are no blasts of hot air or "cold blow" as with other systems. Nearly all geothermal systems on the market have the ability to provide low-cost domestic hot water, further increasing their operating efficiency. Thus, geothermal systems are generally 2.5 to 4 or more times more efficient than resistance heating and water heating alone, and have no combustion or indoor air pollutants. Since there is no outdoor unit (as with air-source heat pumps or the central air conditioners used with combustion-based systems), no weather-related maintenance is required.

Although their installation cost is somewhat higher due to the required underground connections for heat transfer to and from the earth, geothermal systems provide low operating and maintenance cost and greater comfort.

Conclusions
When comparing heating systems, safety, installation cost, operating costs, and maintenance costs must be considered. To simplify the selection process, installation, operating, and maintenance costs can be combined into a life-cycle cost - the cost of ownership over a period of years.

A recent study by the U.S. Environmental Protection Agency showed that geothermal systems generally have the lowest life-cycle cost of all systems available today. The study also shows that geothermal systems have the lowest impact on our environment. And consumers rank their comfort and satisfaction with geothermal systems higher than all others. While a higher initial investment is required, the investment is paid back through low energy bills (enhancing resale value), excellent family safety and real comfort.

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