It doesn't happen often, but sometimes customers call us and tell us that their exhaust hood is leaking grease. We are going to have to ask some questions to narrow that problem down.
Did you just have your hood cleaned? If so, it may not be grease. It may be dirty brown water. If this is the case it isn't altogether uncommon. What happens? Hoods are built by countless craftsmen, using a variety of
kitchen exhaust hood models, but there remains only one type of hood cleaning- -a wet one. The grease exhaust ducts- -all of them- -are welded to the hood and each turn, dip, rise, 90 degree turn, etc... the duct makes on its way to the fan on the outside of the building contain seems in the metal that also have to be welded water tight- -but not all are water tight.
Before a kitchen exhaust hood is put into service, a fire marshal must inspect the fitness of the duct by supervising a light test where a bright bulb is passed through the entire inside of the exhaust hood system duct. If any light can be seen from the outside, the light test is deemed a failure and another light test appointment has to be made after the problems are resolved.
Let me add here that these precautions are taken with fire safety as priority. Still being this sure to seal all seems in the duct, human error will prevail from time to time and leaks will occur.
Grease leaks are happening for the same reason water leaks are happening, only grease is usually thicker and slower.
One more important note. Access doors can also leak. If your system has access doors due to hard to reach access, and many do, the seals on the access door may have failed or the door could be improperly installed.
In any case, the problem must be understood and hopefully resolved.