The Grease Interceptor Capacity Estimator is a practical tool for foodservice professionals, plumbing consultants, and restaurant owners who need to determine the proper size of a grease interceptor for their kitchen drainage system. By analyzing the water flow from connected fixtures and applying standard retention guidelines, this estimator helps ensure your interceptor meets local code requirements, prevents costly sewer blockages, and supports environmental compliance.

How It Works

Sizing Methodology (PDI G-101 Based)

This estimator follows the Plumbing and Drainage Institute (PDI) G-101 standard approach:

Core Formula:

Required Capacity (Gallons) = Total Flow Rate (GPM) × Retention Time (Minutes) × Load Factor

Step 1: Compile Fixture Flow Data

  • Identify every fixture that drains into the interceptor (3-compartment sinks, pre-rinse stations, dishwashers, wok stations, etc.)
  • Record the flow rate for each fixture in Gallons Per Minute (GPM)

Step 2: Set Sizing Parameters

  • Retention Time: The minimum duration wastewater must stay in the interceptor for grease to separate and rise. Most codes require 15-30 minutes.
  • Load Factor (Safety Margin): A multiplier (usually 1.5-2.0) that accounts for peak flow surges and ensures the interceptor has adequate reserve capacity.

Step 3: Select Commercial Size
The calculated capacity is matched to the nearest standard commercial interceptor size:

Standard Sizes (Gallons): 20, 35, 50, 75, 100, 150, 200, 250, 300, 500, 750, 1000

Always round up to the next available size if your calculated value falls between standard options.

ParameterDescriptionDefaultTypical Range
Load FactorSafety margin multiplier for peak flow1.51.0 – 2.5
Retention TimeMinimum time for grease separation (minutes)1510 – 30
Fixture Flow RateGPM for each connected fixtureVaries0 – 50 GPM each
Fixture TypeTypical GPM
3-Compartment Sink7.5 GPM
Pre-Rinse Sink5.0 GPM
Dishwasher (Commercial)15-25 GPM
Wok Station25-40 GPM
Floor Drain (Kitchen)3-5 GPM

FAQ

Q: How do I determine the right interceptor size for a small restaurant?
A: A small restaurant with a 3-compartment sink and dishwasher typically requires a 50-75 gallon interceptor. Use the estimator with your specific fixture GPM values for a precise recommendation.

Q: What are the consequences of an undersized interceptor?
A: An undersized interceptor will need more frequent cleaning, may overflow, and can cause sewer blockages that lead to fines and environmental violations.

Q: What is the recommended cleaning frequency for a grease interceptor?
A: Generally every 30-90 days depending on usage. The interceptor should be cleaned when 25% of its capacity is filled with grease and solids.

References