Oil-fired
heating systems generate heat in a furnace or boiler. Oil systems are less
popular than those using gas because they have a higher initial cost
and limited size availability. They also require a storage tank, oil deliveries,
payment in advance for fuel to be used later, and more maintenance. For instance,
most manufacturers recommend replacing the burner nozzle each year and cleaning
the oil filter monthly. However, when the price of oil is low relative to the
price of other fuels, oil systems are sometimes preferred for their lower operating
cost. Some like oil systems because oil is less flammable than gas.
Most homes using oil use Number 2 heating oil. One gallon of number 2 oil weighs about 7 pounds and contains a heating value of 141,000 BTUs. Oil systems generally have AFUEs ranging from 70% to 80%, and as high as 91% for high efficiency oil condensing furnaces. Oil boilers have AFUE ratings from 50% to 80%.
Although the end result, the flame, appears to be the same, oil combustion is slightly different from gas combustion. Oil is pumped to the burner as a liquid, and contains more impurities than gas does. When oil is transported from a storage tank, a filter installed in the line just before the burner removes sediment and dirt from the oil.
Two
types of burners are common in home heating systems. Most older units have gun-type
burners, which shoot an atomized spray of oil into the burner. Flame retention
head burners are an upgrade to gun burners. Using a high speed blower to force
combustion air through the slots in a cone-shaped combustion head, they are
able to give more turbulence to the entering air stream and confine the flame
to a smaller zone for added heat. In addition, when the boiler is idle, this
type of burner restricts air flow thereby reducing off-cycle heat loss. The
efficiency of older units can be improved by replacing the gun burner with a
flame retention head burner.
The products of combustion pass through the heat exchanger by way of the venting exhaust system, usually consisting of a vent pipe and a chimney. The vent pipe is the connector from furnace to chimney, and the chimney is the vertical shaft leading outdoors.
