Grease Trap Sizing

Grease traps and grease interceptors resist the flow of grease from kitchen wastwater to the sanitary sewer system. The combination of kitchen appliances attached to the grease trap determines the grease trap size. When multiple fixtures (dishwashers, 3-compartment sinks, pot sinks, mop sinks) are connected to the grease trap, grease trap sizing becomes challenging. The location of the appliances in the kitchen may determine if more than one grease trap is required.

Grease Trap Sizing Factors

Passive Grease Interceptor and Grease trap sizing formulas can vary from city to city. Grease traps, grease interceptors, and grease recovery devices are sized with different formulas and strategies. Size of the physical units (holding tank) are key in grease traps and grease interceptors whereas the draining time period is key in the sizing of a grease recovery device.

Grease Trap Sizing

Our Grease Trap Sizing Calculator provides a detailed grease interceptor sizing, grease trap sizing and grease recovery device sizing tool. The grease trap sizing formula and results are printable as well as explained in detail. How to size a grease trap made easier.

Grease Trap / Interceptor sizing has been calculated in various ways in various municipalities. Antiquated codes still exist that use formulas that factor in the number of seats in dining room, Manning Formula, meal serving times, fixture ratings, and restaurant location. Grease Recovery and the life of the grease recovery equipment are of the utmost importance to a successful restaurant as well as the sanitary sewer system.

Is the grease interceptor size large enough to effectively separate grease during peak flow periods? An oversized grease interceptor does not work either. The rotting grease and food solida, left in the interceptor over 30 days, wears away the interceptor as well as emits extremely high levels of hydrogen sulfide.

The failure of grease traps and grease interceptors is when the inflow of wastewater exceeds the capacity of the grease trap. This occurs at restaurant dishwashing peak periods. The wastewater bypasses the grease interceptor due to the hot and rapid outflow from the automatic dishwasher. The grease does not have time to settle and separate from the wastewater. Retention time is the time needed for fats, oil, and grease to separate from the wastewater and settle inside the grease trap. Passive grease traps must be maintained monthly as the capacity diminishes as the grease trap fills. Larger sized units (round up to next size) are frequently implimented by mechanical engineers.

Grease Trap Sizing Complications

Massive Sized Interceptor

Municipal codes frequently disallow automatic dishwashers attached to grease traps. Dishwasher wastewater then discharges directly into the sanitary sewer.

Some Municipal codes force drains to be attached to the grease trap. Minimal grease goes down the drains. Enzymes are frequently used to clean the grout on tiled floors. The enzymes disturb the natural bacteria in the trap allowing the grease to liquefy and pass through trap.

Outside in-ground grease interceptors are frequently not possible due to space restrictions inside and outside of a restaurant. The space in a food court restaurant is extremely limited. The installation of in-ground grease interceptors in congested downtown areas is not conceivable. The space requirements as well as the construction required to install grease interceptors is not always practical. The concept of only allowing a large in-ground grease interceptor to meet compliancy is irrelevant and out-dated. A grease interceptor does not always perform to current grease recovery standards if not maintained on a monthly schedule.

Goslyn Grease Recovery Device Sizing


Goslyn Grease Recovery Device sizing is based on the drainage time of the attached appliances. The size of the 3-compartment sink is a key element. The Goslyn separate the fats, oils, and grease (FOG) from the waste water as it enters the device. Grease free waste water goes down the drain while the FOG is collected in a visible cassette. Waste water from an automatic dishwasher will not bypass a Goslyn as the inflow of waste water in controlled. A full 3-compartment sink will take 1 to 2 minutes to drain if the Goslyn is properly sized. FOG will not enter the sanitary sewer or Septic system. Goslyn separate the grease from multiple fixtures simultaneously.

Grease Trap Size or Performance ?

Size Matters - The Correct Size

More Goslyn Info Environmental Impact Grease Management

Grease Trap Sizing

Grease Trap Sizing
can be a
complicated formula

Dishwashers and
sinks are key
factors in
grease trap size

3 Compartment sink

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Goslyn Ontario - Toronto, Canada - 647-763-4060