The most important advance in oil heating has been the flame retention head oil burner (FRHOB). Furnaces and boilers with FRHOBs have combustion (steady-state) efficiencies of over 80%. Replacing an existing oil burner with an FRHOB is very cost-effective if the existing combustion efficiency is less than 75%. Flame-retention-burner motors run at 3450 rpm and older oil burners run at 1725 rpm motor speed. Looking for the nameplate motor speed can help you discriminate between the flame-retention burners and older models of oil burners.
When a conventional oil burner is replaced with an FRHOB, the burner orifice may be reduced one size—a procedure called derating—which accounts for: the over-sizing of the original burner, the higher efficiency of the FRHOB, and building shell energy improvements. The smaller nozzle may also save a little fuel.
A derated FRHOB burner pushes less excess air through the combustion chamber thereby sending less heat up the chimney. The FRHOB reduces the velocity of flue gases and reduces flue gas temperature. However, flue temperatures shouldn’t fall below 350°F or flue gases could condense, causing corrosion.
If a furnace or boiler has a sound heat exchanger but the oil burner is inefficient or unserviceable, the burner may be replaced by a newer flame-retention burner. The new burner must be tested for efficient and safe operation after installation.
Size the burner and nozzle to match the building’s heat load, making adjustments for new insulation and air sealing done during weatherization.