Soot is not a very friendly word in the vocabulary of anyone in the fuel oil or service business, but in fact it can be the silent killer of systems’ efficiency. Many will often blame it on old equipment and/or the lack of a proper annual system tune up. In speaking with many technicians, I often hear how they are finding that many oil filters, pump strainers and nozzles are not being replaced on an annual basis. Sometimes these components are not ever changed until the system shuts down and often at the most inconvenient time.
Many of you will also say that fuel condition is a major problem along with all of the above. I will agree that it could be a contributor to soot. However, there are other areas that should be taken into consideration. Is the system properly sized, short cycling, improperly adjusted or has the structure in which the system is located been changed?
For example, a finished basement added to compliment the house could be reducing the combustion air requirement for the heating equipment. Perhaps the structure is new with high IR rated doors and windows that are just too tight for the unit to breath. I’m also hearing that several contractors will not install any heating equipment unless outside air is included in the package. Keep in mind that combustion air problems are most noticeable during the height of the heating season because doors and windows are closed for an extended period. I’m also hearing that states and communities have made OSA a must with all new installations. If a piece of equipment is operated in a confined space, air should be ducted to the structure exterior. The general rule is one square inch for every 5,000 Btu of input.
However make sure that you have a copy of NFPA 31 and NFPA 54, as this is where you will find all the information needed to determine combustion air requirements.
I would also mention that start-up and shut down of some older burners can be a soot contributor, even if all service and parts replacement required has been done correctly. The reason takes some thinking about how the nozzle and pump perform. Keep in mind when the pump starts, it starts at atmospheric pressure and continues to reach for a predetermined pressure say from 0 to 100 PSI and this is why soot will develop on start up. On shut down the nozzle will return to atmospheric pressure again creating more soot. So in short you have soot on start up and shut down. This can be eliminated if you just install a nozzle check that is available from the nozzle manufacturers. Now, with the new technology that is built into the new pumps and controls, this issue has been resolved. I would, however, suggest that when setting up a burner for maximum efficiency, pay close attention to the nozzle specification and pressure ratings. Pressure can vary to a level that my shock you, example from 140 PSI to 290 PSI.
In closing, keep in mind that soot is dirty and an insulator that affects efficiency. There are many products available from your supplier that can help to overcome combustion air issues and eliminate sooting.