AMERICA’s Sheet Metal Source

Since 1981

Specialty Duct

Ductwork has a lot of uses besides air conditioning. As "America’s Sheet Metal Source", Spiral Pipe of Texas has been manufacturing a wide variety of air transport systems since 1981.

We fabricate for a variety of applications — from cleanroom and pharmaceutical quality stainless steel exhausts through the big, tough and dirty ducts you’ll see in manufacturing, agriculture and mining.

If it’s metal and transports air, we are your source.


Your Round Solution for Rooftop HVAC Duct Systems

Finally, there is a solution to your rooftop duct system needs that is the right shape, the right material and the right price. We have combined our almost 40 years of quality metal duct fabrication with a willingness to innovate and explore new technologies. The result is PhenoliDuct. We combine the proven technology of our double-wall duct manufacturing with the properties of Kingspan KoolDuct® to give you the perfect rooftop ducting solution.

It’s Round!

Rooftop duct should always be round when possible. The round shape sheds rainwater and prevents excessive snow and ice loads. But for most of the country the main reason is wind. A round duct experiences only about 40% of the wind force a comparable rectangular duct would see. Hanger and support spacings are greater for round ducts. And this is truly a round duct, not an 8 or 12-sided adaptation from rectangular duct. Our standard construction uses our spiral duct as the outer shell and a round metal longitudinal-seam duct for the inner shell. Your performance is the same as for our other round duct products.

It’s Closed-Cell!

Owners and designers want a product that will not wick or retain moisture. The Kingspan KoolDuct® insulation is closed cell.

Exceptional Thermal Performance!

Our standard product uses the KoolDuct 45mm board. This product has an R-value of 12.0. It is machined to fill a 2” annular space in our double-wall construction, and our process eliminates all potential thermal gaps. This is 50% more thermal performance in a 2” insulation product than you would get with fiberglass or elastomeric insulations.

Exceptional Surface Burning Characteristics!

The KoolDuct® board used as our insulation has flame spread and smoke developed indices of 10 when tested per ASTM E84. This greatly out-performs other insulations that struggle — and often fail — to reach the minimum 25/50 indices required by most codes. We can provide desirable characteristics such as fully-welded fittings without worrying about setting the insulation on fire. Our customers can also perform field-modifications to the duct without creating a fire hazard.

It’s Durable!

Sheet metal ducts, and particularly spiral ducts, are proven to be durable in outdoor applications. Other rooftop products have been introduced, including some made with phenolic board. Most are simply one or two layers of insulating board with an external lagging applied. These have neither the strength nor durability of double-wall metal construction.

It Is Easy to Install!

If you have installed double-wall spiral duct, you already know how to install this product. Actually, it’s even easier to install than our fiberglass insulated products. The rigidity of the phenolic board and the close tolerances of our annular construction eliminate the need for an inner coupling. Most installations will only need external bolted companion angle rings or our economical SPOT-Flanges.

Lots of material and fabrication options!

We can provide the inner and outer metal shells as galvanized steel (standard), paint-grip galvanized steel, epoxy powder-coated steel, PVC-coated steel, black iron, aluminized type 1 steel, 3003-H13 aluminum, 304 stainless steel or 316 stainless steel. We can provide the metal shells as spiral duct or longitudinal seam welded duct, and in thicknesses from 10 gauge through 26 gauge. We offer spiral lockseam construction, tack-welded and sealed construction, MIG and TIG welding. We can even offer the product as flat oval or rectangular construction. We can factory-assemble manifolds of duct and fittings to minimize field work. Essentially, we can offer just about all products from our SPOT catalog in PhenoliDuct construction.

Phenomenal Price!

This is the good part. We are a lot less expensive than the other closed-cell insulated duct products — elastomeric, foam-filled and even other phenolic products. We aren’t spending time and money trying to overcome properties that don’t lend themselves to the application. We simply developed a way to use the best rooftop metal duct fabrication — SPOT’s double-wall round spiral duct — with the best rooftop insulation material — Kingspan’s KoolDuct® phenolic system. The result is 50% more R-value at 20-50% less cost.

Insulation Characteristics SPOT PhenoliDuct Fiberglass Fiberglass Johns Manville Permacote® Linacoustic® AP/Armaflex® AP/Armaflex® AP/Armaflex FS® K-Flex® Duct Liner Gray K-Flex® Duct Liner Gray Ductmate PolyArmor™ Ductmate PolyArmor™ PremiPour™ 202M Baytherm® 9912 PTM Dual-Tech® ThermaDuct™ R-8.1 ThermaDuct™ R-12 Johns Manville Spiracoustic Plus® AP/Spiralflex®
Insulation Thickness 1-3/4" 1" 2" 2" 1" 2" 2" 1" 2" 1" 2" 1" 1" 1-3/16" X 2 1-3/16" 1-3/16" 1-3/4" 2" 1"
R-Value 12.0 4.2 8.0 8.0 4.2 8.0 8.0 4.2 8.0 4.2 8.0 6.7 6.6 16.0 8.1 12.0 8.4 4.2
Fiber-Free Yes No No No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes Yes No Yes
Closed Cell (≥90%) Yes No No No Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No
25/50 Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No
Density (PCF) 3.5 1.0 1.0 ~3.8 ~5.0 ~5.0 ~5.0 3 – 4 3 – 4 1.6 1.4 2.0 2.2 3.5 3.5 3.5 ~3.8 ~5.0
Water Absorbtion, % by volume Round 1.15% <3% <3% <3% 0.20% 0.20% 0.20% <0.2% <0.2% 0.24% 0.24% 0.05 3.56% 1.15% 1.15% 1.15% <3% 0.20%
Round Yes Yes Yes Yes No No No No No Yes Yes Yes Yes No No No Yes Yes
Flat Oval Yes Yes Yes Yes No No No No No Yes Yes No No No No No No No
Rectangular Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Yes Yes Yes Yes No
Smoother Metal Inner Airway Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No
Durable External Shell Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Can you weld metal on it without it smoldering, smoking or catching on fire? Yes Yes Yes Yes No No No No No No No No No No No No Yes No
Maximum Pressure WG (positive) 10" 10" 10" 10" 10" 10" 10" 10" 10" WG 10" 10" 6" WG 10"
Maximum Pressure WG (negative) -6" -6" -6" -6" -6" -6" -6" -6" -6" WG -6" -6" -6" WG -6"
Cost $$$ $ $$ $$ $$$$ $$$$$ $$$$$ $$$$ $$$$$ $$ $$$ $$$$ $$$$$ $$$$$$ $$$$ $$$$$ $$ $$$$$
Install Labor $ $ $ $ $ $ $ $ $ $ $ $ $ $$ $$ $$ $ $$
Double-Wall Sheet Metal Double-Wall Foam Filled Built-Up Insulation Board with External Lagging Lined Duct (no inner metal shell)

SPOT AgION Antimicrobial Coated Ductwork

Quality from Start to Finish

Indoor air quality has become a leading environmental issue. Studies have shown that the air we breathe indoors is often more polluted than outdoor air and that 70 or more percent of indoor air quality problems involve HVAC systems. Ductwork manufactured with AgION™ antimicrobial-coated steel helps resolve these contamination issues by providing a second line of defense against destructive microbes.

The demand for antimicrobial products is increasing. More and more owners and engineers are requesting it for its effectiveness in inhibiting the growth of damaging bacteria, mold and fungi. AgION antimicrobial-coated steel ductwork is durable and should be incorporated into HVAC systems for hospitals, pharmaceutical facilities and food processing amenities, schools, daycare centers and nursing homes.

AK Coatings’ AgION Antimicrobial Steel. We are incorporating their steel into our complete line of Heating, Ventilation and Air Conditioning ductwork. SPOT `AgION is our name and available through our knowledgeable team. Please call today for more on our destructive microbe SPOT AgION duct work.


The AgION™ antimicrobial compound is a long-lasting, inorganic material that contains silver ions — a safe and natural antimicrobial agent. The compound has two key components working together to suppress the growth of microbes: Silver Ion (the active agent) and Zeolite (stores the silver ions and releases them).

When moisture is present the Zeolite gives a controlled release of silver ions into the environment. This release provides continuous antimicrobial protection for the product. As the humidity increases, and the environment becomes ideal for bacterial growth, more silver ions are released.

For most types of bacteria, the treated surface will be virtually free of microbial contamination within three to four hours, protecting the product from degradation for the life of the coating. The coating life is a function of the application and surface wear.

Coated products must still be cleaned to insure the surfaces will be free of destructive microbes. This serves as an added cleanliness to support regular cleaning routines between each cleaning. The coating life is a function of the application and surface wear, but could average between 10-30 years depending on the thickness of the coating and the wear it receives.

The coating containing the AgION™ antimicrobial compound shall withstand temperatures not to exceed 350F for an extended period of time.


AK Coatings offer antimicrobial-coated galvanized, carbon and stainless steel products up to 60 inches wide in gauges from .018 inch to .060 inches. Products are also available up to 48 inches wide in gauges from .060 inches to .075 inches. Heavier gauge coating capabilities are currently being developed.

SPOT AgION™ Antimocrobial Steel duct can be produced in rectangular, round, flat oval and thermal acoustical panels as supplied by Spiral Pipe of Texas, Inc. Duct system components shall be manufactured from gauges defined in SMACNA’s Duct Construction Standards – latest edition. Coating containing the antimicrobial compound shall have a hardness of 2H minimum when tested per ASTM D3363.


The AgION™ antimicrobial compound is blended into a paint system and applied to AK products by continuous coil coating. The interior surface is treated with the AgION™ antimicrobial coating uniformly and applied with a minimum thickness of 0.1 mils. An untreated clear coating is applied to the exterior surface of the duct. [If necessary, both surfaces of the ductwork can be treated with the coating containing the AgION™ antimicrobial compound].

Gaps in the coating wider than 1/4” shall be repaired in order to maintain product performance. Repair kits are available in spray or brush applications and can be purchased through Spiral Pipe of Texas to the installing contractor.


Rectangular Ductwork
Round Ductwork
Oval Ductwork
Thermal Acoustical Panels

Maximum Temperature: 350F

Smoke/Flame Spread: Virtually 0


Gauge: 26 gauge to 18 gauge

Width: Maximum 60"


Antimicrobial compound is registered with the EPA (Environmental Protection Agency) and FDA (Food and Drug Administration).

Antimicrobial coated product conforms to Standard 723 – not to exceed flame spread or smoke developed ratings of 25/50.

Antimicrobial coated product complies with ASTM B117, ASTM D247, and ASTM D870

Spiral Pipe of Texas

Our Products

SPOT is taking all precautions during the COVID-19 coronavirus pandemic. We do remain OPEN FOR BUSINESS and stand ready to serve you. We are limiting customer service interactions to PHONE and EMAIL ONLY however our offices are closed to in-person visits.