Orifice Size for a Natural Gas 56,000 Furnace

Finding Size

• There is no standard orifice size for all natural gas furnaces and every brand. Sizes differ, especially based on burner configuration, the size of the furnace itself and how old the furnace is. This makes it difficult to give a clear idea of the right size for a natural gas furnace, but manufacturers tend to make it easy. Orifice sizes are typically machined onto burners, gas valves and other surrounding components for easy reference. Close inspection of the system should reveal the right sizes.

Pilot

• Pilot burners have separate orifices from primary burners. If you are replacing or switching your pilot burner, do not use primary burner measurements. Pilot burners tend to have slightly different measurements, often a fraction of an inch in variance. Many pilot lights come with variable orifices. These can be widened or narrowed to compensate for individual burner requirements and can be adjusted according to instructions in your manual.

Burner

• Primary burner orifice size tends to vary based on the power of the furnace. For a 56,000 Btu rated gas furnace, orifice size tends to stay around 0.136 inches for most furnaces. Others may be larger depending on the brand of furnace. Never assume an average size. Always look in your burner, check with your manufacturer and read your manual to find the right size. Close off gas lines and shut down electrical power before making any changes to the system.

Altitude

• A good orifice sizing chart for your natural gas furnace should show not only the proper orifice size for a 56,000 furnace, but also how the size should change based on altitude. The higher the elevation, the smaller the orifice size needs to be to compensate for difference air pressure. At a couple thousand feet about sea level, orifice sizes can drop to 0.128 or 0.120.