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Grease interceptors are used in plumbing systems to trap greases, oils and solid particles before they can reach the public sewage. For this reason, they are also known as grease traps. A certain oil content is normal in wastewater, and it forms a thin floating layer once it reaches septic tanks and water treatment facilities. However, wastewater from food preparation contains more oil than in other applications, and the waste from multiple commercial kitchens can overwhelm water treatment systems and cause spillage. Lard and other high-viscosity fats can also solidify as they cool down, trapping other solids and blocking sewage pipes.\n
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COMMERCIAL KITCHEN DESIGN | COMMERCIAL KITCHEN PLUMBING | GREASE INTERCEPTORS
Grease interceptors are used in plumbing systems to trap greases, oils and
solid particles before they can reach the public sewage. For this reason, they
are also known as grease traps. A certain oil content is normal in wastewater,
and it forms a thin floating layer once it reaches septic tanks and water
treatment facilities. However, wastewater from food preparation contains more
oil than in other applications, and the waste from multiple commercial kitchens
can overwhelm water treatment systems and cause spillage. Lard and other
high-viscosity fats can also solidify as they cool down, trapping other solids
and blocking sewage pipes.
Grease interceptors should be installed for any commercial kitchen equipment
where grease may be released into drain pipes. Consider that some plumbing
fixtures that do not normally receive grease may be exposed to large amounts
occasionally: for example, floor drains are not normally exposed to large
volumes of grease, but there may be cases where it is spilled on the floor in
large amounts and the floor drains must handle it. Of course, there are also
cases where the use of grease interceptors is obvious. For example, scullery
sinks and meat preparation sinks produce large amounts of grease, oils and
Make sure your grease interceptors are specified
For projects in New York City, only a Registered Design Professional
(RDP) can submit commercial kitchen plumbing designs for approval by
the NYC Department of Buildings, and only a Licensed Master Plumber
(LMP) can carry out the actual installation. Also consider that the NYC
Department of Environmental Protection (DEP) performs routine
maintenance and cleaning.
In addition to NYC-specific requirements, grease interceptors are
subject to national standards such as:
● PDI-G101: Testing and Rating Procedure for Hydro Mechanical
Grease Interceptors (Plumbing and Drainage Institute)
● ASME A112.14.3: Grease Interceptors (American Society of
● ASME A112.14.4: Grease Removal Devices
Grease Interceptor Sizing Procedure
The first step to specify grease interceptors is reviewing the kitchen
layout and determining which equipment must be routed to grease
traps. Interceptors may be specified individually or for multiple fixtures
at once, as allowed by the available space.
After a grease interceptor layout has been proposed, the next step is
calculating the aggregate volume from the fixtures connected to each
unit. Aggregate volume is the maximum volume that can flow through
the interceptor simultaneously, determined by adding the wastewater
volume of individual fixtures plus any required margins.
Department of Environmental Protection provides two tables, each with
interceptor capacity values (in pounds) corresponding to aggregate
volume from kitchen fixtures (in cubic inches).
Kitchen Fixtures Covered by
Kitchen Fixtures Covered by Table II
Food preparation sinks
Floor drains used only for
Any fixture where soup and stock
kettles are discharged
The retaining capacity is calculated separately for the fixtures in each
table and the two values are then added. The tables can be viewed
directly in the NYC Dept. of Environmental Protection website.
and 2,500 cubic inches for Table II fixtures. With these values,
● Table I requires 14 lb of retaining capacity
● Table II requires 20 lb of retaining capacity
● The total grease interceptor capacity is 34 lb.
This value applies if all the kitchen fixtures in the example discharge
into a common interceptor. If multiple grease traps are used, the
procedure is carried out separately for each one. Although the
procedure is straightforward, keep in mind that some exceptions apply:
● For commercial kitchens with floor drains where grease may be
discharged, Table I still applies. However, the aggregate volume
must be increased by 1,540 cubic inches for each floor drain.
● Soup and stock kettles that discharge into a floor drain count
towards the Table II aggregate volume, even if floor drains are
Table I fixtures.
● Table I reaches up to 123,000 cubic inches, while Table II reaches
up to 61,600 cubic inches. If these values are exceeded, the grease
interceptor capacity must be calculated by an NYC Registered
Design Professional, based on data extrapolation.
● The retention capacity of grease interceptors (in pounds) must be
at least twice the numerical value of flowrate through the unit (in
A final requirement is that water flowing through a grease interceptor
must not have a temperature above 180°F.
General Guidelines for Grease Interceptor Installation
A recommendation not only for grease interceptors but for equipment in
general is adhering to manufacturer instructions. A good product can
have poor performance if it used in the wrong application or installed
Grease interceptors are available in recessed, semi-recessed and
on-floor versions. They must be equipped with vented flow control
fittings to keep discharge below the flow capacity specified by the
manufacturer. Using manual valves to reduce flow to a grease
interceptor is not allowed.
After initial installation, grease interceptors must be kept under optimal
operating conditions. Cleaning and grease removal must a part of
routine maintenance, and the units should be accessible for inspection
by the NYC Dept. of Environmental Protection.
requirements are met:
● An NYC Registered Design Professional must file a formal petition.
● The proposed system must deliver equivalent or superior
performance compared with a grease interceptor.
● Equivalency must be demonstrated with detailed documentation
Grease interceptors perform a fundamental role in commercial kitchens,
as well as other applications where significant amounts of grease or oil
are discharged. They are very important for public hygiene, and the NYC
Dept. of Environmental Protection places stringent requirements
regarding their use, while carrying out routine inspection for units in
By working with qualified design engineers, you can ensure your grease
traps are specified properly. This ensures code compliance, offers
hygiene for your staff and customers, and prevents the uncontrolled
discharge of grease and oil into the environment.