Avoid Trane as their outdoor condensing unit coils are made using a unique design called 'Spine-Fin' and are notorious for loading up with cottonwood fluff, spider silk, etc.


I have worked in the HVAC trade and would like to share some up-to-date facts about copper versus aluminum condensing units and evaporator coils.


1a) Money - Copper prices went out of control high when the Chinese economy boomed prior to the Great Recession of 2008. It only reasonable for U.S. manufacturers to anticipate future copper metal price spikes in considering potential future cost and potential copper shortages. Aluminum metal is plentiful, but uses a great deal of electrical energy to refine the ore.

Advantage aluminum.


1b) Aside from the cost of copper metal, aluminum coils are more difficult and costly to manufacture. This is in large measure because it is difficult to join aluminum tubes because of the thin layer of oxide that forms on aluminum. Copper is much easier to join and repair. New aluminum soldering alloys were developed over recent years that have improved the process of producing all-aluminum coils, although it is still remains difficult to repair an aluminum coil in the field.

Advantage copper.


2) Higher refrigerant pressures - New EPA mandated chlorine-free refrigerants replaced long time standard HCFC refrigerant R-22 in 2012. An example of a new refrigerant is Carrier's Puron (which is known in the trade as R-410a) which operates at higher pressure than R-22, so the tubing used in making new condensing and evaporator coils must have thicker walls to resist the higher pressure.

The new refrigerants heat-carrying ability, known as its enthalpy, fluid ounce for ounce, is about half that of R-22. Since about twice the mass flow is needed to move the same quantity of heat, larger coils are needed. Larger coils mean more metal used. A-coils in evaporators (at the furnace end) become N-coils to absorb the heat from the air stream, and condensers (found outdoors to move the heat into the air) must be much larger to handle double the flow
of refrigerant. EPA also mandated higher Seasonal Energy Efficiency Ratios for air conditioners and heat pumps, requiring these coils to be made larger still.

Advantage aluminum.


4) Corrosion - Copper coils are made with aluminum fins mounted in galvanized steel frames, which is a recipe for galvanic corrosion over time. Aluminum metal reacts with the oxygen in the air to produce a thin, but tough oxide coating that protects the underlying metal from corrosion. If the aluminum metal is scratched or scuffed, the protective oxide layer reforms immediately. Aluminum coils are all aluminum, and being homogeneous, do not suffer from galvanic corrosion the way three-metal copper coils do. The protection afforded by the oxide layer is not absolute; animal urine, like dogs sent marking or male cats spraying, and sea salt spray will destroy both copper and aluminum coils.

Advantage aluminum.


4a) Chinese Drywall, More Corrosion - References are made in this thread to Formicary Corrosion a.k.a. Ant Nest Corrosion. Formic acid is an organic acid produced by ants to signal each other, but many organic acids will cause this deep pitting corrosion in copper. Some thread entries blame ants, but not one entry has named the actual cause of most of the recent spate of damage to U.S. HVAC equipment - hydrogen sulfide off-gassed by impurities in imported Chinese drywall. Because of its protective oxide layer, aluminum does not react with hydrogen sulfide the way copper does.

Advantage aluminum.


5) Field serviceability - Repairing aluminum refrigeration tubing is much more challenging than repairing copper tubing. Copper can be heated all the way to cherry red glow without damage. It can be both brazed (temperature over 800 degrees F) or soldered (temperature below 800 degrees F). Aluminum heats up and as the temperature rises, without warning, melts onto a puddle.. When the temperature is tightly controlled, because of that thin, but tenacious layer of aluminum oxide mentioned earlier, solder or braze filler metal alloys have difficulty bonding to aluminum. Recently developed exotic and expensive fluxes are making field repair easier, but some technicians still refuse to even attempt a field repair on an aluminum coil, insisting on replacing it instead.

Advantage copper.



I think it is fair to say the future is all aluminum coils, both because of the cost savings in the cheaper metal, and continuing improvements in aluminum joining and repair techniques.

If you want your new A/C or heat pump investment to last as long as possible, for a few hundred dollars extra, ask you contractor if the make and model they are offering is available with a 'Coastal' or 'Sea-Side' option. Units with this option are made with their coils coated with a very thin, but completely corrosion resistant polymer, and are assembled using stainless steel screws and bolts. They are intended for use near the ocean, but are equally good at resisting corrosion caused by a range urban threats from acid raid to cat pee.