Page 142

NORA Oilheat Technicians Manual

Chapter 7 Combustion Figure 7-16: Effects of leaving a unit operating with a 5 smoke 7-16 Combustion Percent of Fuel Wasted Percent of Combustion Efficiency Net Flue Gas Temperature °F • Obstruction in chimney or at top of chimney • Top of chimney is lower than the peak of the house • Flue pipe diameter is too small. It should never be smaller than the breeching size • Too many 90 degree elbows in the stack • Flue pipe does not have sufficient pitch upward from breeching to thimble; it should be at least ¼" per running foot • Flue pipe extends too far into the chimney flue • Heat exchanger passages are clogged with soot and scale, too restricted, or too baffled • Appliance is overfired; the volume of flame and combustion gases is too great for the heat exchanger design and are creating back pressure or a positive draft over the fire • Unit is underfired, so that the chimney gases never get hot enough to create normal draft conditions • Insufficient ventilation or combustion air in the appliance room, starving the flame for air and draft flow • Improper adjustment of the draft regulator • Differences between breeching and over-fire draft (draft drop): More than .05" difference between the two draft readings usually means trouble. Check for heavy soot deposits in the heat exchanger, particularly if the burner was found with a heavy smoke • Little or no difference between the breeching and over-fire draft: If the stack temperature is high, baffling or heating unit replacement should be considered • Over-fire CO2 higher than breeching CO2: Check for air leaks between top of combustion chamber and heat exchanger outlet (Breeching) • Visible openings for air leakage: Study how the heating unit is put Total Burner Operating Time (Hours)


NORA Oilheat Technicians Manual
To see the actual publication please follow the link above