How to handle exposed ductwork projects
Here are some suggestions
I recently had a son graduate from college. To celebrate, my wife and I took a group out to a week-old new restaurant.
My wife groaned as I took out my cellphone and started taking pictures of the exposed duct system. Hey, it’s what I do for a living. Architecturally exposed duct systems have become popular for a number of different reasons, but as a “duct guy,” I take particular pride in the many successful installations of which I’ve been a part. I’m also curious about how others design, fabricate and install exposed duct systems. I see some great ideas on how to handle some applications. I also see bad installations and things to avoid. As I took pictures of the exposed duct in this brand-new restaurant, all I could think of was “Some people just shouldn’t do exposed ductwork.”
This duct was only 10 feet above the floor and painted red, so it was hard to miss. At various places along the duct there were creases and big dents. The ends of the spiral duct were banged up as if someone pried on them with a screwdriver.
Maybe 99 of 100 guests in that restaurant would have never noticed. But this was not a good exposed duct installation. And I doubt the owner or the architect, walking through the new restaurant, were pleased either. I’ve been around enough though, to understand how this scenario played out. It may not even have been the sheet metal contractor’s fault. These ducts could have been damaged in shipment. The painter may have run into the duct with a scissor lift. Or it could have been the sheet metal contractor’s fault.
Not a good show
The owner may have taken the job with the thought it could be the kind of marquee installation that would advance the business. Then he or she sent two poorly trained technicians to install it, neither of whom had the skill or inclination to do a proper job. Or maybe someone decided to go cheap and just use some right-sized duct that had been lying around for a few years.
No one should be happy with this installation. The problem is this restaurant had to open, and by the time someone may have complained, replacing this duct system would have delayed completion of the project. So, a bad HVAC construction installation gets accepted. And architects, owners and people like me get a little less excited about using exposed duct on the next project.
There were several points where this situation probably could have been avoided without significant delay to the project. There are an estimated 2,000 spiral duct machines in the U.S., so replacing a couple of damaged pieces may cost someone a few dollars, but it shouldn’t take a long time. Or maybe someone should have seen that errant painter on the scissor lift, or those workers banging around and said “Wait, that’s not acceptable.”
Regardless of who was to blame, the fact that a poor installation had to be accepted was the fault of the entire team — designers, fabricators and installers. When ductwork fabrication people like me get together at ASHRAE events or Spiral Duct Manufacturers Association meetings, we frequently have conversations about what needs to be done to ensure a successful installation of an exposed duct system. The following are some guidelines for what should be the responsibilities of all three parts of the team. They mostly apply whether the job is round, rectangular, flat-oval or even fabric.
Define the appearance that will be acceptable. Vague “must look good” specifications don’t work. They are hard to enforce. If dents and dings are not acceptable, state that in the contract documents. I often see projects where a minimum gauge is called for specifically to prevent dents and dings, especially in athletic facilities where expected use involves lots of basketballs hitting the duct. It’s an option available to the design team in all applications, though for the sake of cost you might just want to use standard gauges and make sure everyone is just a little more careful with the duct if you don’t expect mistreatment after installation.
There should also be a designated representative who will approve the installation in a timely manner so corrections can be made without delaying the project.
Define acceptable features. It should be OK — especially on exposed duct jobs — to insist on specific features or manufacturers. I confess a preference for the look of noncorrugated versus corrugated spiral duct myself, but I know plenty of people that feel just the opposite. Some duct manufacturers — round, flat-oval and rectangular — have put a lot of thought into ways to make a better looking product. If they have some features you want in your installation, call them out.
The duct must function properly and in accordance with construction codes. This starts with requiring the ductwork to be sealed. I’ve heard the statement “You don’t have to seal it because it’s in a conditioned space” many times from contractors that should have stuck with installing window air conditioners. They’re wrong. There is no exposed-duct exception to ASHRAE standard 90.1. It states quite specifically that “Ductwork and all plenums with pressure class ratings shall be constructed to seal Class A.” The function of the duct system is not to simply fill the box with air; it is to place the air so that it provides comfort to the occupants. And those occupants are not sitting in the rafters.
As the industry moves toward more energy efficient systems, eliminating leakage — as well as proper duct design and selection of the right air-projection methods — can help achieve occupant comfort with less volume of conditioned air.
Improperly installed and uninsulated ductwork can lead to condensation in humid environments.
Is the duct going to be painted and who will be responsible for painting the duct? You would be surprised how often you can’t get an answer to those questions from the project documents. Several duct manufacturers now offer painted products, so specifying one can help get you the look you want. If a separate contractor on the job site will be doing the painting, make sure the specifications for the duct and the painting align. Otherwise, you may be spending money for the duct material that is not necessary to meet the painting requirements. It’s equally important to know if the duct will not be painted so things like mill and shop markings on the outside can be avoided.
Does the duct need to be insulated? This is an engineering decision, not a contractor decision. I live in Houston, where for six months each year the outside temperature and the relative humidity are in a daily race to see which can get close to 100 first. Combine that with 55°F conditioned air, a minimally insulated roof and ducts running too close to an outside doorway and you can have an indoor waterfall.
I’ve been to restaurants where entire rows of tables are unusable in August because of condensation dripping from the ducts. Yes, insulation costs money and everyone wants to lower the cost of building their project. But it is the responsibility of the engineer to determine the need for duct installation and defend that need to the owner and contractor. Duct insulation may add to the project cost, but it pales with potential lost revenue from unused space or the cost of one slip-and-fall accident. Eliminating it where needed is not “value engineering.”
Have a written and specific guideline for fabricating exposed duct systems, preferably with pictures. Owners, designers and installers have an idea in their head of their expectation for an exposed duct system. But then they get quotes for “One lot of…” and a price. They need a way to differentiate between you and all the other quotes to insure they get the system they want.
If you have a desirable innovation or feature, give it a name or a brief description. It will be a lot easier for the owner, designer or installer to ask for your product, or at least set the bar for your competitors.
Know the specification and standards, and assure customers will get products built to them. I’ve seen a lot of projects where the duct looks acceptable coming off the truck but the problems start showing up when they turn the HVAC system on. These problems are especially noticeable on an exposed duct system. Massive dust streaks down the sides of the duct a few months after installation show poor seams and missing sealant. I got called to one job where a 44-inch duct terminated in an end cap, right over the store entrance. The fabrication contractor used too light of a gauge on the cap and it became a giant bass drum.
Yes, the duct must look good, but first it must perform. Know that your flaws will be there for everyone to see.
This red-painted spiral ductwork has dents, likely due to poor handling. Pictures courtesy of Bob Reid.
Have a shipping strategy. Exposed duct should be treated more kindly than regular duct. Your shipping team can undo all the careful work and planning you put into making a good exposed duct product. But owners, designers and installers can go a little overboard on their expectations, too. If things go wrong, everyone will want to know why you didn’t wrap each piece and crate them. You need to communicate early what alternative method you use to minimize damage. The right balance of product care and cost is a competitive advantage.
Have a backup plan and let your customer know what it is. Exposed duct systems should normally arrive at the job site just in time to be installed so they do not get damaged from sitting around. The usual reason damaged or unfit duct gets used is that replacing it as a normal first-come, first-served shop order would delay the project. Even though ducts almost never leave the shop damaged, you end up sharing much of the blame — and sometimes the claim — because you leave them little alternative to using damaged duct.
In this case, workers decided to put insulation around the duct after it had been installed. The insulation should have been put in prior.
Have a process and plan in place, and a price, for repair and replacement of damaged duct. Depending on complexity, it could be up to a three-day turnaround on replacement at a set premium. I once did a large stadium with complex assemblies and our plan for minor damage was an auto paint and body shop that demonstrated their ability to repair dents before painting. We never had to use them — proving the old adage that those with a backup plan seldom have to use it.
A good exposed duct installation should cost a little more than one that will never be seen above a ceiling. It doesn’t have to cost a lot more, but all of those special design features, shipping strategies and backup plans cost money. Think of it as insurance — you hope you never need it, but it won’t ruin you if the unexpected happens.
Exposed duct jobs are your showcase. Treat them as such. Your competitors will. Use your most talented installers.
Make sure everyone knows the duct will be exposed. This may not be apparent to fabricators, especially if they’re working from your bill of materials. I once had a job where the contractor sent a group of helpers to the jobsite to unload the trucks instead of interrupting their installation crew. The duct was carefully packed, but large. When the installation crew started to lift the duct in the air they found long scrapes and dents running the entire length of the bottom of the duct — the side everyone would see. It turned out that the unloading crew didn’t know anything about the job, didn’t see a forklift they could use, and simply dragged the duct off the back of the truck. A little information would have avoided a big problem.
Don’t let your purchasing agent ruin the job. My simple rule is that the longer your field crew touches the duct, the uglier it will be. That’s not intended to be a knock on the field crews. Labor-reducing features and functions performed in the controlled environment of the shop will almost always recoup far more than their cost on exposed jobs. Longer lengths, gasketed joints, factory painting, manifolds and assemblies, installed taps and diffusers, packaging and protection, coordination drawings — all those things will give purchasing agents heart attacks when they look at what they’re used to paying for duct. But decisions on where to spend a little money to save a lot of money should be guided by the ones that have to sell the final product: project superintendents and managers.
Poorly made and installed taps can lead to leaks.
Have someone who understands how air functions in an open space look at the job before you begin. Otherwise, pictures of your installation will wind up on a wall of shame somewhere. I’ve seen countless installations where a supply register blows straight into the return air grille, short-circuiting 25 percent or more of the designed airflow and decreasing duct pressure to the point that downstream registers can no longer perform as designed. I see registers blowing into walls and beams because no one coordinated the layouts. Noise problems, dust problems, mold problems, condensation problems are all avoidable for someone who can visualize the operating duct system in the finished environment, but not so obvious to someone that only sees sizes on a duct calculator or just a bill of materials.
A successful exposed duct job relies on all three parts of the team — design, fabrication and installation — understanding what it takes to make a good-looking and well-functioning exposed duct system. If any of the three failed, it could undermine the efforts of the others. So to ensure success, you really need to start with a fourth part of this team: the owner. That person needs to select a design team who understands what it will take to get the job done right. Then he or she needs to trust their judgement and hold them accountable for designing and specifying a system that will meet the requirements of both appearance and performance. The owner needs to communicate what visible features are expected from the duct system. Insist that fabricators and installers demonstrate the ability to provide the system he describes. Finally, the owner must be ready to disallow lower prices from designers, fabricators and installers that do not meet the requirements. Getting ugly duct is one thing. But getting duct that performs poorly will end up costing far more than any momentary savings.
This example of dust-covered duct should have had sealant put around its joints.
I’ve seen far too many applications where owners were forced to go back after a restaurant opening and have the exposed ducts wrapped with insulation, which was far more expensive than having it done during construction. They do it, even though the cost will be several thousand dollars, because each booth or table that cannot be used on days the humidity is too high represents hundreds of dollars each of those days in lost revenue.
Not everyone should try to do exposed duct systems. There are plenty of other projects out there that do not require the quality of both appearance and performance, Take the time to describe what makes your projects good. That will give owners and the other members of the team the reasons to make you part of their next project.