Comparing Systems
Central heating 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.
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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.
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Heat Transfer Systems
Non-combustion or heat transfer systems include heat pumps and
geoexchange systems. Heat pumps operate by capturing heat from outdoor
air and transferring it inside of a home or business. Geoexchange
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 geoexchange systems
also provide domestic hot water at low operating costs.
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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.
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Geoexchange Systems
More recently, even more advanced and efficient heating and cooling
systems have emerged using the geoexchange 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,
geoexchange 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 geoexchange systems on the market have the ability to provide
low-cost domestic hot water, further increasing their operating
efficiency. Thus, geoexchange 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,
geoexchange systems provide low operating and maintenance cost and
greater comfort.
About Carbon Monoxide:
When inhaled, carbon monoxide interferes with the delivery of oxygen
throughout the body, and can cause unconsciousness and death. Even all
amounts of this colorless, odorless gas cause symptoms ranging from
headaches, dizziness, weakness, nausea, confusion, and disorientation,
to fatigue. Prolonged exposure may cause permanent brain damage.
Children, pregnant women, the elderly, and people with anemia or with
heart or respiratory problems are especially sensitive to carbon
monoxide exposure.
Over 1,500 people die and over 10,000 reportedly take ill from carbon
monoxide exposure each year. Many carbon monoxide poisonings are not
detected, as doctors confuse its symptoms with influenza or food
poisoning.
The U.S. Consumer Product Safety Commission and others recommended the
installation of carbon monoxide detectors, although it is not clear that
detectors will protect consumers from low levels of carbon monoxide over
long periods of time. Detectors have also been the subject of recalls by
their manufacturer due to failure to alarm at dangerous levels of carbon
monoxide.
Carbon monoxide is an insidious killer. To help assure safe operation,
combustion-based heating systems should be checked frequently for indoor
air pollution hazards. Other sources of carbon monoxide, such as
barbeque grills and automobiles, should never be operated in enclosed
spaces.
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. The table below compares the various types of central heating
systems:
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), or geoexchange
systems (with their low operating and maintenance costs and high levels
of comfort).
A study by the U.S. Environmental Protection Agency showed that
geoexchange systems have the lowest life-cycle cost of all systems
available today. The study also shows that geoexchange systems have the
lowest impact on our environment. And consumers rank their comfort and
satisfaction with geoexchange 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.