Steam Boilers & Determining the Appropriate Nozzle Size

Function

• One of the primary purposes of a nozzle is to improve steam quality and heating efficiency. In steam boilers, feeders supply water that is heated to produce steam. The steam is pushed out of a nozzle attached to the steam outlet in the boiler. On average, boiler nozzles deliver steam at speeds between 4,000 to 5,000 feet per minute, according to the U.S. Department of Energy publication, “Steam Pressure Reduction: Opportunities and Issues.” As steam pressure decreases, the nozzle's steam velocity increases. Generally, to increase the velocity of steam, you must install a larger-sized nozzle.

Burner

• The size of the burner nozzle in steam boilers determines the system's ability to produce not only high quality steam, but also latent heat for the radiator. Heating systems require a certain amount of oil to fire the burner and fuel the steam boiler. The oil burner nozzle is responsible for distributing this oil into the burner tank. If the nozzle's gallon per hour (GPH) rate is lower than the GPH rate required to fire the burner, then you will need to replace the nozzle with a larger size. Install burner nozzles that are compatible with the boiler's GPH firing rate to avoid condensation in the pipes. This will allow the boiler to produce enough steam to fill the radiators.

Load Design

• When replacing boiler nozzles, ensure that the steam nozzle size matches the boiler’s design load. Design load reflects the boilers ability to handle fluctuations in energy use during the operation of appliances and other home equipment. The size of the boiler’s steam reservoir will help determine the proper nozzle size for the system. For example, purchasing an oversized nozzle can increase the release of pollutants and decrease thermal efficiency.

Operating Pressure

• The volume of steam and distance from the steam nozzle to the water level in the boiler will also affect steam quality. Operating pressure affects the size and rate of the entrainment, or capture of water droplets in the rising steam. A lower operating pressure in steam boilers will determine the size of the nozzle. For example, nozzles with lower steam pressures will produce larger water bubbles, higher levels of entrainment and higher speeds out of the boiler.