Heating - Outside Source for
Technology Snapshot & Benefits:
Combustion units for heating buildings
benefit from drawing combustion air directly from the outside using sealed and
insulated ductwork. The advantages of this are two-fold: 1) conservation of
warm indoor room air; and 2) reduced infiltration of cold outside air through
cracks in windows, doors, and elsewhere in the building envelope. When
combustion air is drawn from a heated basement room, it returns to the outside
via a chimney after supporting combustion in the firebox. This loss of air
slightly depressurizes the interior of the building, and pressure recovery is
most likely through leaks to the outside. Bringing combustion air to the firebox
through an insulated and sealed duct solves this problem.
Estimated Cost Savings:
A typical home furnace, rated at 80,000
Btu/hour, may operate at a duty cycle of 50% (it is operating about half of the
time). To support this combustion, X cubic feet of air per hour are required,
or 24X cubic feet of air per day, more or less, depending upon how much your
furnace runs. Savings accrue from retaining warm indoor room air and
particularly from reduced infiltration of cold outside air. Drafts,
particularly annoying to occupants, are eliminated or greatly reduced. In
dollars, this translates to a potential savings of 5-10 cents on the
dollar for the heating costs of the typical home or building owner. For an
average heating bill of $200 per month, this translates into a savings of $10-20
per month, directly to the bottom line.
Enabling ductwork may present logistical
issues to rooms that are already finished. These are often easily overcome.
The value of this modification depends upon
the annual heating requirement of your furnace or boiler. The
The National Climatic Data Center provides an historical record of departures of average daily
temperatures from a reference temperature of 65 degrees F. This information is
available as "Heating Degree-Days per Year" and provides a very useful estimate
of how often your heating plant will run.
Installation (Getting It
The air intake source should
be covered with a screen to prevent access by rodents and pests.
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