Grease Trap Sizing Calculator
Size grease interceptors for commercial kitchens and food service establishments. Calculate capacity requirements based on fixture loads and code requirements.
Grease Interceptor Sizing Guide
Flow Rate Calculation
Sum fixture flow rates and apply peak load factors
Account for establishment type and code requirements
Capacity Requirements
Based on flow rate and required retention time
Includes storage capacity for grease accumulation
Unit Selection
Gravity interceptors for high flow, outdoor installation
Hydromechanical for compact, indoor applications
System Configuration
Kitchen Fixtures
Kitchen Equipment
Food Preparation
Cooking Equipment
Grease Interceptor Guide
Gravity vs Hydromechanical
• Gravity: 500-1500+ gal, outdoor installation, 30-min retention
• Hydromechanical: 40-150 gal, indoor installation, 2-min retention
• Choose gravity for: High flow (>20 GPM), outdoor space available
• Choose hydromechanical for: Space constraints, indoor installation
Code Requirements
• UPC: Standard sizing based on fixture flow rates
• IPC: 20% higher flow, 10% larger capacity requirements
• Local codes may require additional sizing factors
• Some jurisdictions require automatic cleaning systems
Maintenance Requirements
• Fast food: Weekly cleaning minimum
• Full service restaurant: Bi-weekly to monthly
• Low grease load: Monthly to quarterly
• Document cleaning frequency for health department
Grease Interceptor Sizing Formulas & Code Requirements
Step-by-Step Sizing Process
- 1. Flow Rate Assessment: Calculate total GPM from all connected fixtures
- 2. Peak Load Factor: Apply multipliers for establishment type and usage patterns
- 3. Code Compliance: Apply local code requirements and safety factors
- 4. Capacity Calculation: Determine required volume based on flow and retention time
- 5. Storage Allowance: Add capacity for grease accumulation between cleanings
- 6. Unit Selection: Choose gravity or hydromechanical based on application
Core Sizing Calculations
Basic Flow Rate:
GPM_total = Σ(Fixture_GPM × Count)
Sum all connected fixture flow rates
Design Flow Rate:
GPM_design = GPM_total × Peak_Factor × Code_Factor
Apply peak load and code multipliers
Required Capacity (Gravity):
Capacity = GPM_design × 30 min × (1 + Storage%)
30-minute retention for gravity interceptors
Required Capacity (Hydromechanical):
Capacity = GPM_design × 2 min × (1 + Storage%)
2-minute retention for hydromechanical units
Peak Load & Code Factors
Establishment Type Multipliers:
Fast Food: 1.5x
Full Restaurant: 1.2x
Cafeteria: 1.0x
Hotel/Hospital: 0.8-1.3x
Code Requirements:
UPC: 1.0x flow, 1.0x capacity
IPC: 1.2x flow, 1.1x capacity
Local: 1.5x flow, 1.3x capacity
Grease Load & Cleaning Frequency
High Grease Load Operations:
Fast food restaurants
Frying operations
Bakeries with fryers
Cleaning: Weekly minimum
Medium Grease Load Operations:
Full service restaurants
Hotel kitchens
School cafeterias
Cleaning: Bi-weekly to monthly
Low Grease Load Operations:
Coffee shops
Minimal cooking facilities
Prep-only kitchens
Cleaning: Monthly to quarterly
Performance & Efficiency Factors
Gravity Interceptor Efficiency:
Grease removal: 90-95%
Solids removal: 85-90%
Temperature sensitivity: Low
Flow rate sensitivity: Medium
Hydromechanical Efficiency:
Grease removal: 85-90%
Solids removal: 80-85%
Temperature sensitivity: High
Flow rate sensitivity: High
Variable Definitions & Standards
GPM = Gallons per minute
DFU = Drainage fixture units
Storage% = Grease accumulation allowance
Peak_Factor = Establishment type multiplier
Code_Factor = Local code multiplier
Retention = Required detention time
Capacity = Interceptor volume (gallons)
Efficiency = Grease removal percentage
Design Standards:
UPC Chapter 10
IPC Chapter 10
ASME A112.14.3 (Hydromechanical)
ASME A112.14.4 (Gravity)
Installation Requirements & Maintenance Standards
Installation Guidelines
Gravity Interceptor Installation
- • Location: Outdoor, accessible for pumping
- • Depth: Typically 4-8 feet underground
- • Access: 24" minimum access opening
- • Venting: Required per local codes
- • Slope: 1-2% slope to interceptor
Hydromechanical Installation
- • Location: Indoor, under sinks or nearby
- • Clearance: 18" minimum for service access
- • Electrical: 115V connection required
- • Drain: Cleanout connection needed
- • Mounting: Floor or wall mounted options
Maintenance Requirements by Application
Fast Food Operations
- • Cleaning frequency: Weekly
- • Grease removal: When 25% full
- • Documentation: Required by health dept
- • Emergency cleaning: 48hr response
Full Service Restaurants
- • Cleaning frequency: Bi-weekly
- • Grease removal: When 25% full
- • Inspection: Monthly visual check
- • Records: 3-year minimum retention
Low-Volume Operations
- • Cleaning frequency: Monthly
- • Grease removal: When 30% full
- • Self-service: Some units allow
- • Monitoring: Quarterly assessment
Grease Trap Sizing Questions & Answers
How do I decide between a gravity interceptor and a hydromechanical unit?
Gravity interceptors (per UPC 1003.3.4) require 30-minute retention time and work best for flows over 20 GPM. They're passive systems that separate grease through flotation. Hydromechanical units (per PDI G101 standard) use mechanical separation in 2 minutes but are limited to specific flow rates. Choose gravity for outdoor installations and variable flows, hydromechanical for tight indoor spaces under 50 GPM.
What happens if I undersize the grease trap?
You'll be cleaning it constantly, and it still won't work right. Undersized units can't handle peak flows, so grease just flows through without separating. You'll get grease in your drainage system, potential backups, and probably a very unhappy health inspector. It's way cheaper to go a size up than to deal with constant maintenance and potential line stoppages. Plus, most health departments require specific sizing based on your fixture count anyway.
How often do these things really need to be cleaned?
Per health department regulations, most jurisdictions require cleaning when grease and solids reach 25% of total capacity. High-volume operations (fast food, fryers): weekly minimum. Medium-volume (full-service restaurants): bi-weekly to monthly. Low-volume (coffee shops): monthly to quarterly. Document all maintenance per FDA Food Code Section 4-204.112 - inspectors will verify compliance records.
Do I need to connect every sink to the grease trap?
No, just the ones that handle grease. Dish machines, prep sinks, pot sinks - yes. Hand wash sinks, mop sinks, and toilets - no. Some places try to connect everything thinking it's simpler, but that just dilutes the grease and makes the trap less effective. The code usually specifies which fixtures need to go through the interceptor. When in doubt, if grease goes down the drain, it needs to go through the trap.
What's the deal with local codes being different from UPC or IPC?
Local jurisdictions can be more restrictive than the model codes. Some cities require larger interceptors because they've had problems with grease in their sewer systems. Others might require automatic cleaning systems or specific types of units. Always check with the local authority first - their requirements trump the model codes. This calculator has a "local code" option that adds extra safety factors, but you still need to verify the actual local requirements.
Can I install a grease trap myself, or do I need a contractor?
Gravity interceptors almost always need a licensed contractor because you're excavating and connecting to the sewer system. Hydromechanical units under sinks might be DIY-friendly if you're handy with plumbing, but check local permits first. Many jurisdictions require permits and inspections regardless. Even if you can legally do it yourself, consider the warranty implications and whether you want to be responsible if something goes wrong.
How much do these systems typically cost to install?
Small hydromechanical units run $2,000-5,000 installed. Gravity interceptors are $5,000-15,000+ depending on size and excavation requirements. The equipment is usually about 40% of the total cost - the rest is labor, excavation, permits, and connections. Factor in $500-2,000 annually for maintenance depending on your cleaning frequency. It's not cheap, but it's way less than dealing with sewer backups or health department fines.
What about those "biological" grease treatment systems I've heard about?
They're basically grease traps with bacteria added to digest the grease. They can work, but they're finicky - the bacteria need the right temperature, pH, and detention time to work properly. Many health departments don't recognize them as equivalent to traditional interceptors. If you're considering one, make sure it's approved by your local authority first. Traditional grease traps are proven technology - biological systems are still proving themselves.
Why do some calculations give me wildly different sizes?
Because there's no single standard for peak load factors and safety margins. Some calculators are conservative and add big multipliers, others are more aggressive. Manufacturer calculators sometimes push you toward larger units. Local codes vary widely too. The basic flow rate calculation is pretty standard, but everything after that can vary. When in doubt, check with local authorities about their specific requirements and sizing methods.
What maintenance should I be doing besides pump-outs?
Check the baffles and inlet/outlet pipes for blockages, make sure the grease layer isn't too thick, and keep an eye on odors which indicate problems. For hydromechanical units, clean the strainer baskets regularly and check that moving parts are working. Document everything - take photos if possible. Train kitchen staff on what can and can't go down the drains. Good daily practices prevent most grease trap problems.
Are there specific code requirements I should know about?
Yes - UPC Section 1003 and IPC Section 1003.3 specify grease interceptor requirements. Most jurisdictions require interceptors for food service establishments over 20 seats or with specific equipment. Size calculations typically follow the 1 GPM per meal served method or fixture unit calculations per code tables. Always verify local amendments as they often add stricter requirements than model codes.
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