Choosing between spiral and rectangular ductwork might seem minor, but it quietly determines your energy bills and comfort for decades. More contractors are switching to spiral whenever space allows.
Better Airflow = Lower Costs
Round pipes maximize airflow with minimal surface contact. Lab tests show spiral systems deliver 20-30% lower pressure drops than rectangular ducts of the same capacity. Every bit of pressure saved means smaller fans, lower energy costs, and quieter operation.
Dramatic Leak Reduction
The numbers are eye-opening:
- Spiral systems: Class 6 leakage ratings (one continuous seam)
- Rectangular systems: Class 12+ leakage (seams everywhere)
- Real-world test: 490 CFM leakage (rectangular) vs. 36 CFM (spiral)—that's 90% less air loss
Faster Installation
Per 100 feet of ductwork:
- Spiral: 5-10 pieces, 25-35% less labor
- Rectangular: 20-25 pieces, 40-50 joints to seal
Spiral arrives in 10-20 foot lengths that slide together. Rectangular needs flanging, welding, and extensive sealing.
Quieter Operation
Rectangular ducts "pop" and drum with pressure changes. Spiral's curved walls are rigid and create smoother airflow—perfect for offices, schools, and healthcare facilities.
The Bottom Line
Spiral systems typically cut fan energy costs by 10-20% annually and often pay for themselves in under three years, even before factoring in installation savings.
When to Use Each
Choose spiral when you have space for maximum efficiency and easier installation.
Stick with rectangular for:
- Tight vertical shafts
- Retrofit projects with existing connections
- Spaces where ceiling height is critical
The smart approach? Use rectangular only where space forces your hand, then let spiral handle everything else. The numbers don't lie—round ductwork delivers better performance and long-term savings.
Final Verdict: Spiral Ductwork Saves More
If your project has the space, spiral ductwork is the clear winner in airflow, installation efficiency, noise reduction, and cost savings. The lower leakage rates, reduced labor, and better performance can pay for themselves in under three years.
The smart strategy? Use rectangular ductwork only where absolutely necessary, and let spiral ducts do the heavy lifting everywhere else.