Mid-Efficiency (Noncondensing) Oil Furnace
A typical noncondensing, mid-efficiency oil furnace uses 28 to 33 percent less fuel oil than a conventional oil furnace to produce the same amount of heat. Its operation is characterized by significantly lower combustion and dilution air requirements.
The internal components of a typical mid-efficiency oil furnace are illustrated in Figure 12-4. The high-static oil burner fires into the combustion chamber, commonly made of a heat-resistant ceramic material. Air for combustion is drawn into an intake opening on the burner assembly by a small motor where it mixes with the fuel oil and ignites. The hot combustion gases then pass through the heat exchanger and are eventually expelled through an insulated flue pipe to the outdoors. A separate, larger blower (some- times called the indoor blower or furnace fan), forces air across the outer surface of the heat exchanger, extracts heat, and forces the heat out into the rooms and spaces of the house. The two air streams never mix.
Many of these mid-efficiency furnaces do not require a connection to a chimney. They pass the combustion gases though an insulated vent pipe that extends directly through the sidewall of the structure. A barometric damper is not required in the more efficient furnaces. Some use the forced draft of a high-static oil burner to vent the combustion gases. Others use sealed combustion with a high-static oil burner.
The mid-efficiency oil furnace is equipped with a safety shutoff device in case of draft problems. The other controls are similar to those found on conventional oil furnaces.