Comparing HVAC Systems

Central heating & cooling systems have been considered a necessity in our homes and businesses for many years. When comparing available systems, consumers should carefully consider safety, installation cost, operating costs, maintenance costs, and comfort.

Types of Systems

There are two basic types of 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 in the early part of the century. 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. Unfortunately, there are a number of serious safety and related maintenance concerns with these systems.

Some combustion-based systems present an explosion hazard if the storage or delivery of their fuel is not carefully controlled. Explosions due to improperly installed or maintained gas pipes and delivery systems are often in the news. Since these systems require a flame to operate, failures or improper installation of system components (for example, heat exchanger, damper, chimney, or flue) can result in property loss to fire. Fortunately, smoke detectors have saved many lives that might have been lost to fires caused by combustion-based heating systems.

In addition to heat, combustion-based heating systems also create by-products such as carbon monoxide. Carbon monoxide is a result of the incomplete burning of fuel in combustion-based systems. Incorrectly installed systems, chimneys that are blocked by birds nests, or downdrafting can cause carbon monoxide to remain inside of buildings. This is especially dangerous in modern, well-sealed buildings, where it is difficult for outside combustion air to reach the furnace, and where carbon monoxide can be trapped and build up over time. Furnaces, water heaters, and other appliances must be properly vented outside.

Combustion-based systems that deliver heat through ducts present occasional “blasts” of hot air. This not only reduces comfort directly, but tends to dehumidify the air. The addition of a central humidifier (with its associated installation, operating, and maintenance costs) can correct this humidity problem.

Combustion based central heating systems are often coupled with low-efficiency central air conditioners. This raises installation and operating costs significantly, while adding an entirely separate unit to be maintained.

Heat Transfer Systems

Non-combustion or heat transfer systems include air-source heat pumps and geothermal heat pumps (GHPs). Air-source heat pumps operate by capturing heat from outdoor air and transferring it inside of a home or business, while 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 GHP 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 as a matter of course. 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.

Much less electricity is used to move heat rather than create it, making heat pumps more economical than resistance heating. However, in all but the most moderate climates, the heating ability of the heat pump is limited by freezing outdoor temperatures. So electric resistance heat is used to supplement outdoor-air-source heat pump during the coldest weather, preventing “cold blow.”

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 Heat Pump Systems

More recently, even more advanced and efficient heating and cooling systems have emerged using heat transfer to and from the earth. 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, GHP 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 GHP systems on the market have the ability to provide low-cost domestic hot water, further increasing their operating efficiency. Thus, GHP 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, GHP systems provide low operating and maintenance cost and greater comfort.


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. The table below compares the various types of central heating systems:


Installation Cost


Maintenance Cost
A Concern
Air-Source heat pump

Consumers who take the necessary steps to insure the safety of combustion-based systems (frequent inspection and maintenance, smoke detectors, carbon-monoxide detectors, and other safety precautions) may wish to consider these moderate life-cycle cost systems. Others should consider more advanced heat transfer systems — heat pumps (with their moderate installation, operating, and maintenance costs), orGHP systems (with their low operating and maintenance costs and high levels of comfort).

A recent study by the U.S. Environmental Protection Agency showed that GHP systems generally have the lowest life-cycle cost of all systems available today. The study also shows that GHP systems have the lowest impact on our environment. And consumers rank their comfort and satisfaction with GHP 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.