How Much Fuel Oil Do Steam Boilers Use?

Steam Boilers

• Steam boilers are being phased out in favor of other forms of heating in many places. Typically found in older homes, steam boilers bring water in the tank to a boil by heating it with a flame from below. As the water heats, it converts to steam. This steam flows in the top of heating pipes to the radiators in each room of your house where it radiates the heat from the steam into the room. By releasing its heat, the steam in the radiators condenses back to water and returns to the boiler at the bottom of the same pipes it traveled to the radiator in. Steam boilers can use oil, natural gas, propane or electricity to heat the water in the tank.

Type of Fuel Oil

• The type of fuel oil you are using will help determine the amount needed. The different fuel oil grades create varying amounts of heat when burned. According to "Building Environments HVAC Systems" by Delmar, et al., grade #1 oil generates 137,000 BTUs per hour and grade #2 generates 141,000 BTUs per hour. Grade #4 produces 146,000 BTUs per hour, 148,000 BTUs per hour are created by grade #5 fuel oil and grade #6 oil yields 150,000 BTUs per hour. There is no grade #3 oil. BTU stands for "British Thermal Unit," a measurement of energy that tells you how much heat the system can produce.

Steam Boiler Efficiency

• The efficiency of the steam boiler will help you to determine how well the system makes use of the oil it is burning. The efficiency is a ratio of the heat output of the boiler to the heat input from burning fuel. Manufacturers put the efficiency of their individual unit on a product information sticker affixed to the boiler. Generally, clean, well-maintained oil-firing steam boilers have an efficiency of around 87 percent, according to "Control & Instrumentation Technology in HVAC: PCs & Environmental Controls" by Michael Hordeski.

Firing Rate

• The amount of fuel oil used in a steam boiler is called the firing rate, expressed in gallons per hour of fuel used. To determine the firing rate for your steam boiler, look for the gross rating on the side of the boiler. This number will be in BTUs per hour and reflects the heat input. Multiply the fuel rating of the type of fuel oil you are using by the efficiency of the unit. The gross rating is divided by this number to find the firing rate of the steam boiler in gallons per hour, which will help you create an estimate of how much fuel oil you'll need to keep the steam boiler running.