Grease Duct

Our fully welded grease ducts vent flammable grease-laden vapors, usually from commercial cooking equipment, to outside the building. We ensure our duct fabrication is in compliance with NFPA 96 (“Standard Ventilation Control and Fire Protection of Commercial Cooking Operations”). Check your building and local fire code for special requirements.

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United Team Mechanical quality

Our Grease Duct

A fully welded grease duct system is a large task to undertake. Not only is the pipe heavy and difficult to handle, but it also has little to no margin for error. You must have rigging, certified welding, and pipefitting skills to get your grease duct installed properly. Don’t hesitate to ask our installation department for help – we are professionals, this is what we do for a living and we actually enjoy it.

Quality Suppliers

Even the smallest hole in a weld can cause issues with your grease duct. In order to mitigate this risk we have an automated transverse seam welder to ensure our quality. Our grease duct is commonly formed from 16 gauge black iron, but we can fabricate grease duct from most all types of material in various gauges.

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HVAC Fabrication and Manufacturing

Grease Duct Options

Square Duct

  • All sizes (typical length is 59″ but can be prefabricated in longer lengths)

Pipe Diameter

  • 4″ – 60″

Pipe Length

  • Any size from 1″ – 120″ (standard length is 60″ or 120″ depending on diameter.)

Metal Type

  • Black iron and stainless steel

Metal Gauge

  • 1/4″ plate
  • 12 gauge
  • 14 gauge
  • 16 gauge

Serving These Industries

Commercial Kitchens


Food Processing

Pneumatic Conveying

Advantages of Grease Duct

Fully Welded

Fully welded grease ducts are also light tested for any pin hole leaks. The weld seam will hold and is less susceptible to leaking than any other type of seam.

Minimal On-site Welding

Grease duct is notorious for being difficult to connect in the field since access is poor at best. Our team will prefabricate and weld sections together to allow easier joint connection in the field.


Although other “easier” options are often touted, black iron welded grease duct is a tried and true method that allows you to make the duct to the exact dimensions called out on the prints.


We are required to have the grease duct meet the NFPA 96 standards when fabrication and installation.

Readily Available

16ga black iron steel is a common item that is found at most all sheet metal shops and can be quickly fabricated to your specifications.


Slope and access doors can be fabricated to allow easy access to maintain and provide the slope necessary.

Frequently Asked Questions

What is a grease duct?

Similar to any other duct, it is a metal series of pipe that typically runs from an exterior exhaust fan to an interior hood. The typical grease duct is fully welded 16ga black iron, or as specified in local code. This allows the air carrying grease particulates to be safely exhausted outside a building.

Are there alternatives to welded grease duct?

Yes – there are a few options of a “clamp together” system that is pre-insulated and welded. The transverse connections are all done onsite with caulking and clamps.

How to clean grease duct?

If you do not professionally clean grease duct, we would recommend hiring a professional to help maintain the ductwork. Grease duct should be built and installed sloping either toward the kitchen hood or the exhaust fan, and access doors are periodically spaced at change of directions or specific clean-out spots. Start cleaning at these easy access points.

Can I replace an existing grease duct?

The short answer is yes, but it can become very costly due to the fully welded duct that is typically fire wrapped and surrounded by conduit, structure, and the like. We highly recommend replacing grease duct only when it is absolutely necessary or at the time of an existing remodel.

How to size grease duct?

As sizing any other ducting system, you must start with your equipment needs. If your kitchen equipment calls for a certain amount of air then you must match the fan and the ducting to accommodate. Always start with your kitchen equipment needs and work backwards.

How difficult is installing grease duct?

The typical 16ga black iron fully welded grease duct always proves to be a challenge for a number of reasons.

  1. Grease duct requires a slop
  2. Typically you can install the duct before other trades but the tie-in pieces must wait until after the hood is installed
  3. The tie-in fittings are usually being welded in very tight spaces trying to weld stainless and mild steel together. Nonetheless, we have become very proficient at installing grease duct, as it is our job.
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