Furnace Oil Preheating Temperature

What does the furnace manufacturer's manual say?

The #1 used oil heater manufacture Clean Burn has 2 heaters in the burner.

The block heater set point is 140F, and the proving switch is 125 F. The proving switch prevents the burner from trying to fire until the block heater reaches 125F.

The nozzle heater temp. is 120 F.

We burn #4 and #5 oil. We don't even look at the #6 oil. That is bad stuff. It is cheap but when you get it on you it is like a Tattoo. Burn your clothes and trade trucks.

Tom Silver

No. 5 FO will require preheating at 215-220 degF. Most efficient firing will be when the fuel oil viscosity is such that optimum atomizing is achieved. Burner tips are calibrated for a given flow. Flow is a function of orifice diameter, line pressure and fuel viscosity which is a function of temperature.

Been in the oil burning business for 18 years and hold several patents.

Fuel oil #4 or #5 is basicly used oil from the auto industry. Flash point is 125 F. and flows great at 100 F., Reccomended temp is 140 to 160 F. The oil begains to cook and make deposits in the system at 165 F.

The Heavy Oil is #6 or Bunker C, It must be heated to the 215 F. plus.

Tom Silver

Thanks for setting the record straight on FO #6.

For storing and transferring cold fuel and if no preheat source is available, fuel pumpabilty can be enhanced by adding a dispersant.

The preheating temperature depends on the grade of oil you are using. The idea of preheating is to make the oil flowable and reduce the viscosity. The Cst 180 oil has a viscosity of 180 at 50 deg C. If the oil has to flow freely with at reduced viscosity of around 50, then you have to heat the oil app. to 100 deg C. Ofcourse, the other criterion is the Pour point and flash point. If the pour point of the fuel oil is around 70 deg C, the rule of thumb is 20 degrees more. Make sure that the fuel oil flash point is much above the preheating temperature. i would heat to 95 to 100 deg C.