How is a grease interceptor sized in Phoenix?

Add the drainage fixture units (DFU) of every grease-bearing fixture, multiply by 3 gallons per minute, then by 12 minutes of retention, or 17 minutes if there is a garbage disposal. Phoenix's smallest gravity interceptor is 500 gallons, so anything under that rounds up to 500.

When can a Phoenix restaurant use a small grease trap instead of an outdoor interceptor?

When it has four or fewer grease-bearing fixtures and no garbage disposal or dishwasher. The trap is sized by fixture count, from 20 gpm and 40 pounds for one fixture up to 50 gpm and 100 pounds for four.

What is the smallest grease interceptor Chandler allows?

Chandler's chart starts at 750 gallons for 0 to 21 drainage fixture units and runs to 3,000 gallons at 342. Above 342 DFU an Arizona registered professional engineer has to design it.

Do hand sinks count toward grease interceptor size?

No. Phoenix's worksheet excludes hand sinks, and they shouldn't drain to the grease line at all. Condensate and cooler drain lines also stay off it.

Is this calculator's answer final?

No. It runs the same worksheet the city uses, but plan review makes the call, and the inspector recounts fixtures in the field. Use it to budget and plan, then submit the city's worksheet with your plans.

Free Tool

Grease Interceptor Sizing Calculator

Count your kitchen's fixtures and get the size Phoenix or Chandler will expect, worked out with the formulas from each city's own worksheet.

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Short answer

In Phoenix, a gravity grease interceptor holds your fixtures' drainage fixture units times 3 gallons per minute times 12 minutes of retention (17 with a garbage disposal), with a 500-gallon minimum. Kitchens with four or fewer fixtures and no disposal or dishwasher can use a small trap instead. Chandler sizes from a DFU chart starting at 750 gallons.

Size your interceptor

Floor drain

2", 3" or 4" trap · 2 DFU each

Floor sink

Skip floor sinks already counted with a sink below · 3 DFU each

Trough drain

2", 3" or 4" trap · 2 DFU each

Trough drain at tilt or soup kettle

2" trap x 2 · 4 DFU each

Trough drain at tilt or soup kettle

3" trap x 2 · 6 DFU each

Trough drain at tilt or soup kettle

4" trap x 2 · 8 DFU each

Mop or service sink

1½" or 2" trap · 3 DFU each

Sink with food waste

Scullery, prep or prewash sink (hand sinks excluded) · 3 DFU each

Food waste disposal

2" trap · 3 DFU each

Dishwasher

2" trap arm x 2 · 4 DFU each

Dishwasher

3" trap arm x 2 · 6 DFU each

Dishwasher

4" trap arm x 2 · 8 DFU each

Phoenix result

Add the grease-bearing fixtures in your kitchen to see the size.

An estimate for planning, not a plan approval. The city's plan reviewer and inspector make the final call, and they count fixtures in the field.

How Phoenix sizes a gravity interceptor

Phoenix's Fats, Oils and Grease manual gives one formula: capacity in gallons equals total drainage fixture units (DFU) times 3 gallons per minute times the retention time. Retention is 12 minutes, or 17 minutes if the kitchen has a food waste disposal. The DFU values come from the city's fixture count worksheet, which is what the calculator uses.

The city's own example: one food prep sink (3 DFU), a mop sink (3 DFU) and three floor drains (2 DFU each) add up to 12 DFU. 12 × 3 × 12 = 432 gallons, so the interceptor is sized at the 500-gallon minimum. Simple as that.

A 500-gallon unit needs at least two manways and two compartments; 750 gallons and up needs three manways. It has to be an approved model, and a kitchen fed by a grinder pump sizes from the pump's flow rate times 17 instead. See the Phoenix fixture count rule and replacement plan review.

Hydromechanical traps in Phoenix

The small indoor traps are sized by how many fixtures drain to them, under Phoenix's amendment to IPC Table 1003.3.5.1. Only kitchens with up to four fixtures and no disposal or dishwasher can use one, and a two-way cleanout goes on the discharge side.

Fixtures connected	Flow rating (gpm)	Grease capacity (lb)
1	20	40
2	25	50
3	35	70
4	50	100

Chandler's DFU chart

Chandler amends IPC 1003.3.7 to size gravity interceptors from a chart. Fixture DFUs come from drain size (IPC Table 709.2), and a dishwasher counts 2 DFU per gallon per minute of its rated flow.

Total DFU	Interceptor volume (gallons)
0 to 21	750
22 to 35	1,000
36 to 90	1,250
91 to 172	1,500
173 to 216	2,000
217 to 307	2,500
308 to 342	3,000
Over 342	Designed by an Arizona registered engineer

More on the Chandler sizing chart and Chandler's food service FOG device rules.

Other Valley cities

Other cities size interceptors by the IPC or UPC as they have amended them, and some add a review by their pretreatment staff. Compare them on the Valley grease trap rules by city page, and read the UPC sizing method if your city uses the UPC.

Once it's installed, the interceptor needs a pumping schedule and three years of records. Our printable grease trap maintenance log covers what Phoenix, Scottsdale and Surprise ask for. Running a restaurant? Start with our restaurant plumbing guide.

Sources

FAQ

Grease interceptor sizing questions

Anything else, call (602) 675-1555.

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