Galvanized Ductwork 101: Gauges, G-Ratings, and What We Use at K & E

When you’re choosing duct, two specs matter most: steel gauge (thickness) and galvanized coating weight (zinc layer, e.g., G60 or G90). Thicker steel resists dents and spans farther; more zinc slows rust at seams and scratches. (Intro to coating weights and ASTM overview: GalvInfoNote, U. S. Steel quick conversions.)

Gauge (Thickness): What it Means

  • 30 ga (thin, light): common on small-diameter round pipe for low-pressure runs.
    Pros: light, inexpensive. Cons: dents easily; not ideal for long spans or rough handling.

  • 28 ga: step up in stiffness for round and small fittings.
    Pros: better durability. Cons: slightly higher cost/weight.

  • 26 ga: standard for many residential trunks and larger fittings.
    Pros: sturdier panels, cleaner seams. Cons: heavier, pricier than 28–30.

  • 24 ga: for larger trunks, long spans, light commercial, or tougher handling.
    Pros: strong, holds shape, reduces oil-canning. Cons: more cost/weight; may need heavier hangers.

Rule of thumb: As duct gets larger, longer, or exposed to abuse, go thicker (lower gauge number). (SMACNA context: see the HVAC Duct Construction Standards.)

G-Ratings (Zinc Coating): Why G60 vs. G90 Matters

The G-number is total zinc weight on both sides (ASTM A653). More zinc = better corrosion resistance.

  • G60: balanced protection for interior duct in conditioned spaces.

  • G90: extra margin for damp areas, basements, crawlspaces, garages, rooftop curbs, or where condensation risk is higher.

Important: G60 vs. G90 does not change steel thickness—only the protective zinc layer. (Definitions and conversions: GalvInfoNote, G60 vs G90 explainer.)

K & E Shop Standards

  • We stock and fabricate 26 ga and 24 ga as our core thicknesses.

  • For both 26 ga and 24 ga we use G60 and G90 zinc coatings depending on environment.

  • Heavier gauges (22 ga, 20 ga) are used as the job and specifications require (size, pressure class, span, and reinforcement).

  • For sealing, we follow UL 181 listed mastics/tapes for HVAC duct systems. (UL 181 context.)

Quick Picks (Save & Share)

  • Small round runs (dry interior): 28–30 ga, G60

  • Typical residential trunks/returns: 26 ga, G60

  • Basement/crawl/garage or any condensation risk: 26 ga, G90 (or 24 ga if large spans)

  • Large trunks/long spans/light commercial: 24 ga, G60/G90 per environment

  • Outdoor/rooftop/curb: G90 minimum; consider 24 ga or heavier

Advantages & Tradeoffs at a Glance

  • Thicker gauge (24 vs. 26): more rigidity, fewer oil-cans, longer spans → higher cost/weight.

  • Higher zinc (G90 vs. G60): longer rust resistance → slightly higher material cost.

  • Smart combo: match gauge to size/span and G-rating to moisture risk.

Helpful Definitions & Deep Dives

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Why Young People Should Join the Trades: Building Real Skills, Real Things, and a Real Future

Pallet Of Ductwork

Every fitting tells a story.

This photo might look like a stack of shiny metal boxes to some, but to us, it's a week of progress, planning, and precision. Each piece sitting on this pallet—offsets, reducers, elbows, takeoffs—is the result of a design process that begins with tape measures in tight basements, field notes scribbled on scrap paper, and digital cut files run through our plasma table.

Here’s what you’re looking at:

  • A mix of custom transitions, each fabricated to fit unique site conditions

  • A couple of rectangular elbows, carefully bent to maintain airflow and minimize pressure loss

  • A set of square-to-round reducers, which help marry mismatched systems

  • Stacks of unformed blanks, labeled and ready to bend, notch, and hem

All this galvanized sheet metal will be installed in real homes and buildings within days—maybe even hours. It will hide behind drywall, above ceilings, and inside mechanical rooms. And though you may never see it again, your comfort will rely on its craftsmanship for years to come.

Why It Matters

Most homeowners never think about their ductwork until something goes wrong. But behind every well-ventilated space is a network of sheet metal fittings fabricated by hand and eye—cut to spec, sealed tight, and installed by a crew that knows airflow is as much art as science.

These aren’t generic pieces pulled off a shelf. Every job has quirks—maybe the furnace sits low, or the joists don’t line up, or the return drop has to squeeze past plumbing. That’s where skilled fabrication makes all the difference.

From Shop Floor to Air Flow

This pallet is ready for delivery, and the team who built it will probably never see the finished job. That’s just how it goes in this line of work. But we take pride in knowing that when someone turns up the thermostat or gets a blast of cool air in a second-story bedroom, this pile of metal helped make it happen.

So here’s to the overlooked, the hidden, the hard to reach. Here’s to ductwork that fits like a glove.

A Trade Worth Learning

If you’re a young person out there wondering what to do with your hands, your head, and your future—look again at that photo.

Those fittings didn’t come from a factory overseas. They were made right here, by people who know how to read a job, cut a pattern, fire up a plasma table, and build something real. There’s value in that. There’s pride in that. And there’s opportunity in it, too.

The trades are full of aging experts and open jobs. The work is steady, the pay is solid, and the impact is immediate. You don’t need a mountain of student debt to get started—you need curiosity, grit, and the willingness to learn.

We need more hands on deck. If you like working with tools, solving puzzles, and doing work that actually matters, this is a career path worth walking. And we’re always looking for people ready to take that first step.

Want to see more behind the scenes?
We’re planning a photo series showing how fittings go from CAD file to cut sheet to installed product. Follow along on the blog or sign up for our newsletter to get updates.

📸 Photo taken in our shop last week. Every job is different, and every fitting gets made with care.
🔧 If you’re a homeowner planning a retrofit or a contractor needing fast turnarounds, reach out. We build to fit, not force.

The Best Way to Paint Galvanized Metal

Painting galvanized metal requires some preparation to ensure proper adhesion and durability. Galvanized metal has a zinc coating to protect it from corrosion, but this coating can make it challenging for paint to adhere. Here's the best process:

1. Clean the Surface

  • Remove dirt and grease: Use a degreaser or soapy water to remove any oils, dirt, or grease from the surface. Rinse thoroughly and allow it to dry.

  • Eliminate white rust: If there is white rust (a chalky residue from the zinc), scrub it off with a wire brush or fine-grit sandpaper.

2. Scuff the Surface

  • Use fine sandpaper (120–150 grit) or a scuff pad to lightly roughen the surface. This helps the primer and paint adhere better.

  • Wipe down the surface with a clean, damp cloth to remove sanding dust.

3. Choose the Right Primer

  • Use a primer specifically designed for galvanized metal, such as a zinc-rich or self-etching primer. These primers adhere well to zinc-coated surfaces and create a good base for paint.

  • Apply the primer in thin, even coats according to the manufacturer’s instructions. Allow it to dry completely.

4. Select the Proper Paint

  • Opt for an acrylic latex paint or a paint specifically formulated for galvanized metal. Avoid alkyd- or oil-based paints unless they are explicitly labeled for galvanized surfaces, as these can react poorly with the zinc coating.

5. Paint Application

  • Apply the paint using a brush, roller, or spray, depending on the size and shape of the surface.

  • Use thin, even coats and let each coat dry completely before applying the next one. Typically, two coats are sufficient for full coverage.

6. Cure and Protect

  • Allow the paint to cure fully before subjecting the surface to heavy use or outdoor elements.

  • For additional protection, you can apply a clear sealant or topcoat if needed.

Tips:

  • New galvanized metal: If the metal is newly galvanized, it may have a shiny surface that makes adhesion difficult. Let it weather for a few weeks or use a vinegar solution (1:1 vinegar and water) to etch the surface before priming.

  • Test adhesion: Before painting a large area, test the primer and paint on a small, inconspicuous spot to ensure they adhere well.

Following these steps will ensure your painted galvanized metal is durable and looks great for years.

Custom One Inch Lined Plenum Boxes and Plenum Sleeves

Depending on the job, commercial or residential, there may be a need for fiber glass acoustical lining on the inside of the duct work. Duct liner, in it’s simplest form, is there to help reduce noise and provide a minimal R-value—much less than duct wrap—to provide more consistent temperatures and energy efficiency.

K&E Sheet Metal’s morning was full of duct liner, one inch thick to be exact. The thickness can range from 1/2” to 2”. Our shop mostly deals with half-inch and one-inch. Occasionally, we will get a spec (specification) for 1 1/2” or 2”, but it’s rare for the size jobs—commercial vs. Industrial— we fabricate for. In future, as the shop grows, that could change.

The liner is cut to size, adhered to the metal with glue, and then secured with corresponding weld pins.

Plenum Sleeves with liner glued; waiting for pins to be welded down.

Plenum Sleeves with liner glued; waiting for pins to be welded down.

Plenums and Sleeves in multiple stages of the lining process

Plenums and Sleeves in multiple stages of the lining process

Steve finishing up weld pinning some plenum sleeves

Steve finishing up weld pinning some plenum sleeves

Joe placing pins for the next step

Joe placing pins for the next step

Finished and ready for pickup

Finished and ready for pickup



Square to Round Monday

Happy Monday! The humidity has arrived in the fabrication shop, as the rains continue here in the Northeast. The floors are coated with a perfect glaze of condensation from the annoying Spring weather patterns. Rain is getting tiresome. Frustrating, but not something to get worked up over. Air conditioning to the rescue!

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We move on. HVAC sheet metal fabrication stops for no weather! The square to rounds must go on!

We are busy and the name of the game today is square to round fabrication. Our shop is limited in the fact that we don’t currently have a spot welder for assembling our square to round fittings. We rivet them. Why not weld? Valid Question. One that many of you fabricators may be asking.

Truth be told, I’ve had different spot welders over the years and have never been thrilled with the results. Collars were continually popping off in the field, making it harder for our customers to get their job done efficiently. So we began riveting, which does take longer, but there is no worrying about failure in the field.

I am aware that a water cooled spot welder would be the way to go. However, it’s just not in the budget at this time. We invested heavily in equipment over the last few years and the focus is on managing that debt. We will get there.

The picture below shows multiple flat stock body patterns of square to round duct fittings after being cut on the plasma table. They are marked to start the bending process.

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Collars for the round portion of the fittings have been built, ready for installation after the guys have assembled the main body of the custom fittings. We usually fabricate the collars first so they are ready to go!

Custom Collars for Square to Rounds

Custom Collars for Square to Rounds

We had a minor issue with the hand beader for the square to rounds. Below, Steve is working diligently to fix the problem.

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We use the manual bead roller to crimp the top—the round end—of the fitting body. The crimp helps to make easier the installation of the collar on the fitting. We then switch out the crimping dyes for the bead dye, which helps to secure the collar to the square to round body. We finish the job with a few rivets.

Crimping

Crimping

Final Bead with Rivets

Final Bead with Rivets

We are currently fabricating an order of 75 square to rounds. They take time and we want to make sure each one is done to the best of our ability. Occasionally, that means sacrificing some speed. I think the trade-off is worth it.

Next on the docket…Custom plenum drops for a couple rooftop heating and cooling units!! Joe is starting that process this afternoon. Sheet number one has finished cutting; next we clear the table, cut the remnants for recycling and use the scrap for other items in the shop. Possibly another square to round!

Joe clearing the plasma table.

Joe clearing the plasma table.

Sheet Metal Cutting Tools: Straight and Bulldog Tin Snips

Why are my cuts coming out so jagged!? Why don't these snips cut a radius well? Why do all of my long cuts A.) Take so long and B.) Have all these little notches every inch or so?

You may or may not have asked yourself these questions or many others while hacking through a piece of tin. 

I've had all these frustrations over the course of my career and some of those issues come down to experience cutting with any kind of tin snip by hand. However, another answer could be that you may be using the wrong snips for the job. One size does not fit all when it comes to sheet metal cutting tools. 

The one tool that I would have gold plated and mounted on the wall of my office is a pair of Straight Tin Snips. They are on the front of our company T-Shirts and will forever be a building block of any micro tin shop.

Straight Tin Snips I use daily

Straight Tin Snips I use daily

Known as Lather Snips to some, I have always labeled them as straight cut tin snips or shears. I have spent over 15 years of my working life cutting straight duct, plenums and fittings by hand with these and other kinds of tin snips. However, these were by far the Labron James of snips in my Tin Knockers tool bag and on the sheet metal fabrication table.

The manufacturer will tell you wide curves can also be cut, and to a point, you can with the Straight Cut. However, I would argue that the longer handle Bulldog Pattern Snips provide an easier cut when dealing with radius shearing. The Bulldogs are for "nibbling" heavier gauge and they do a great job in that forum. But they do a much better job than the straight cut snips when you have to cut a 40" flat elbow cheek and especially when cutting smaller radius lines by hand. Bulldogs saved me a lot of frustration on those days when fittings prioirized the schedule. 

Bulldog Tin Snips We Use Each Day

Bulldog Tin Snips We Use Each Day

The straight cut snips hang up too much as you make your way through the radius. They can't make the corner nice, especially on those tighter curves. Think of a good handling car versus a bad one. Both vehicles can make the turn. However, you can feel the difference if you've driven the car that really handles well in the corner. It can make all the difference when time is of the essence. 

Having both pairs of snips at your disposal can only help your fabrication prowess. 

Every sheet metal worker, roofer or HVAC technician will have a pair of Straight Tin Shears at the ready. They are tried and true; the backbone of a Tin Knockers tool bag. I would bet many of them carry a pair of Bulldogs as well.

Today at K & E Sheet Metal they have taken a back seat to the CNC plasma table and pneumatic jump shear, but they still hold tremendous value in our shop on a daily basis.  They were the tools that built this company to where we could afford the plasma table and jump shear.

If you're working in the field and you don't have a pair in your tool bag, do yourself a favor. And if your're starting a small fabrication shop, they are a must. Those aviator snips you may have picked up at the local Home Depot are immensely important when it comes to sheet metal cutting tools, but they will soak up your time and forearm strength in seconds.

The Straight Cut Tin Snips and Bulldog Pattern Snips will help take care of that problem and keep your cuts straight and true.  

Happy Cutting!