The biggest difference when using exposed versus concealed spiral is aesthetics. Obviously, you would like all of your spiral to go together easily, be quiet and heat and cool the space well. But with exposed spiral, you have the added need for “pretty” because now your customers will see it. Here are the top five things we at Hennemuth Metal Fabricators (HMF) consider when sending exposed duct out to our customers. 

insulate                        Insulated board


1.    Are you planning to keep the traditional galvanized metal finish, or will you be painting it

If you are planning to paint your spiral, you will need to use galvanneal instead of galvanized metal. This is a type of paint grip material that will allow your paint to adhere better to your spiral. Typically, the spiral is painted after it’s installed but it can also be powder coated for a more durable finish.   

2.    Will all your connections look the same? 

Depending on the diameter of pipe you are using for your project, your connection types can vary. At HMF, we use a flanged connection for pipe and fittings over 20 inches in diameter. For spiral 20 inches or less, we use a gasketed connection (coupler). 

In a case where you have a 20” piece of pipe exposed along with an 18” piece of pipe the transition, it could look sloppy or unbalanced to your customer’s eyes. In this case, we would consider doing a flanged connection for the smaller pipe as well to keep a uniform look. Keep in mind, there are different types of flange connections. HMF offers the HFC single bolt flange with an overring. The HFC flange is very cost effective because it saves our contractors a considerable amount of time in the field. There is no need for screws or applying gasket. The flange has a gasket already incorporated in the over ring and is tightened down with one single bolt. 

different hanger

Different hangers.

 3.    What type of registers will you use? 

The most popular options are a curved register that directly mounts to and matches the radius of the pipe, a universal spiral register, or a register box with a typical sidewall or double deflection register. Yes, all of the options get the job done, but the curved register offers you a seamless look to complete your exposed job. 

4.    How will you hang your spiral? 

Again, there are many options out there to use to hang your spiral, but not all of the options are aesthetically pleasing. Our first choice would be using a gripple loop to hang your project. This specific hanging material not only saves you field labor, but also gives you a clean line and almost disappears into the backdrop. Other popular options that HMF carries are a 1” hanging strap or allthread with strut.

paint grip

Galvanized, paint grip and powder-coated. 

5.    Does your project require a certain R-value to meet code or condensation concerns? 

If so, we would recommend going with an internally lined spiral and using duct board liner. Duct board will satisfy the R-Value needed without affecting your overall look and typically is cheaper than the traditional double wall spiral. 

spiral register

       Hennemuth Metal Fabricators has three different spiral register options.  


Brett Barker is a shop foreman and estimator at Hennemuth Metal Fabricators.