Finned Tube Types

A practical comparison of the six fin types we produce: how each one is made, what it costs relative to the others, and which duty it suits.

Comparison table

Type	Fin attachment	Contact resistance	Max metal temp.	Relative cost	Best for
Extruded (bimetal)	Extruded from sleeve	Very low	250 °C	Medium	Air coolers, clean air, best efficiency
Embedded (G)	Locked in machined groove	Low	400 °C	Medium-high	High-temperature air coolers
L / LL / KL	Tension wound	Medium	250–300 °C	Low	Clean air, cost-driven projects
HF welded	Welded strip	None (metallurgical)	600 °C+	Medium	Economisers, flue gas, high temp
Laser welded	Laser-welded strip	None (metallurgical)	700 °C	High	Stainless, thin fins, high purity
Integral	Rolled from tube wall	None (same metal)	400 °C	Medium	Chillers, condensers, compact bundles

How to read the table

Contact resistance is the thermal penalty at the fin-to-tube joint. For a mechanically wound fin it grows over time as the fin relaxes; for a welded or integral fin it is effectively zero and stays zero. The maximum metal temperature is a practical limit, not a theoretical one: aluminium loses strength and creeps above roughly 250 °C, which is what governs the L, LL, KL and extruded families.

The two questions that decide the type

1. What is the metal temperature? Below 250 °C the choice is economic; above 350 °C only welded or embedded constructions are stable.
2. What is in the air? Clean air allows thin aluminium fins; dust, ash or corrosive gas pushes you towards steel fins, wider pitches and welded joints.

Everything else — fin height, pitch, thickness — is then optimised inside the chosen family. The next page explains the selection process step by step.