What Decides Furnace Nozzle Dimensions?

Combustion Requirements

• Oil furnaces rely on the principle of continuous combustion. This means that once the furnace begins to run, it continuously burns oil that's sprayed in via the nozzle. By contrast, a car engine also burns sprayed-in fuel but uses spark plugs to ignite individual combustions as part of a non-continuous cycle. Furnace engineers adjust nozzle dimensions to allow for the proper flow rate that facilitates continuous combusting, ensuring the furnace has an adequate supply of both oil and oxygen to keep burning.

Need for Efficiency

• Oil furnaces need to be efficient to make effective use of heating oil. Nozzle dimensions control efficiency in a number of ways, and the need for efficiency limits the dimensions of nozzles. For example, the angle of the nozzle determines where the fuel enters the combustion chamber and how quickly it ignites. The precise dimensions of the nozzle's swirl chamber, which oil passes through shortly before being vaporized, are based on how much surface area the oil droplets need to have when they are emitted and heated.

Furnace Type

• Different types of furnaces also require nozzles with varying dimensions. For example, larger furnaces intended to heat larger buildings need nozzles that can handle a greater flow rate and higher pressure than the nozzles in smaller furnaces. Nozzles also vary in terms of external dimensions, which vary from one manufacturer to another.

Industry Standards

• Although manufacturer specifications and furnace types determine nozzle dimensions, the oil heating industry also specifies standards for nozzle dimensions. According to oil furnace manufacturer Delavan, the oil heating industry recognizes more than 20 acceptable flow rates for furnace nozzles and six spray angles. Manufacturers can choose from among nozzles with dimensions that meet these industry standards based on their specific applications and design goals.