How Coil Replacement Affects Performance & Dependability

swcoil_superadminCoil Performance, Coil Replacement, Uncategorized


Eventually, all the coils or the entire unit will need replacing.  In commercial and industrial systems, coil (component) replacement is the norm due to the tremendous expense and down time of an entire new system.  The larger the system tonnage, the larger the price gap and replacement becomes a no brainer.


To begin with, today’s coil selections for packaged equipment almost never have a service factor for performance due to the heightened competition to provide high efficiency with the lightest weight at the lowest cost.  Even larger system coil selections provide only marginal service performance guarantees.  These factors create “marginal coil construction” that can cause problems providing comfortable heating and air conditioning within the conditioned space.

How does this happen?  Over time, most coils start to load with dirt, debris and foreign materials.  The length of time and the degree of the coil loading is all based on the types of filtration, the individual unit system maintenance schedule, and the severity of the foreign material exposure.  For example, the clean office unit in an office park may have totally different requirements than an office building located in an industrial site.  The types of filters and the filter replacement schedule will also be different.  Additionally, all coils need to have their finned-tube surfaces cleaned, and once again, the cleaning schedule must be based on the application and the system’s environment.

When a coil is loaded with foreign material, the overall performance is drastically reduced.  Fan performance is based on supplying a volume of air versus a total resistance. The original calculation is based on these two factors, and the result is a designated motor horsepower and drive component selection (pulleys, belts etc.).  If coil resistance is very high, the supply CFM volume falls.  If the CFM falls 20%, the overall BTUH capacity will do the same.

Another forgotten aspect of coil loading is the insulation factor of foreign material that reduces heat transfer. In HVAC coils, the calculations of performance are based on the transfer of cold to warm or warm to cold through the tubes and fins and into the air.  More dirt leads to more insulation between these two streams which reduces heat transfer.


Any owner of an HVAC system needs to have a minimum of quality operation over time. One of the major reasons why coils can play a negative role in system dependability is based on two major items.

Many coils in HVAC units have integral problems because of terrible unitary designs. In other words, you are receiving “a lemon” from the outset.  Condenser coils are not properly braced from excess vibration from compressors and condenser fans.  There are also micro channel coils that can’t stand up to the high refrigerant pressures and normal wear and tear of the condenser coil application.  Many coils are not protected against air side corrosion (salt laden air and the like).  Evaporator coils are so light duty that leaks start appearing in the distributor hardware and at return bend areas.   In other words, the race to deliver tonnage at the lowest cost produces system components that can be very light duty creating operating problems very early in their life cycle.

Lack of scheduled maintenance is a huge issue, and it’s not always the fault of the servicing contractor.  The problem may also be an owner that doesn’t have an adequate budget for maintaining its systems. This becomes more prominent in bad economies, recessions, and low-end real estate markets.  With some HVAC systems, the damage is done over time.  The negative payback is that there is so much down time that the owner is forced to keep replacing coils and eventually the entire unit.

Only 20% of all coils in HVAC installations make it to old age.  There are many factors today that influence coil problems and subsequent replacement.  At the time of HVAC design, it’s important to select quality consulting engineers and the proper maintenance requirements during the unit’s life cycles.  These selections are all based on budgets and funds during the selection process.

Southwest Coil represents USA Coil & Air exclusively in the Southwest Region.  Together, we have been in the business of replacing coils for 4+ decades, and our existence is based on diagnosing problems and creating solutions that could have been avoided if identified early.  Most coil problems require the services of a professional coil engineer who understands why the coil(s) have failed and offers you timely, quality replacements that alleviate future problems.  We believe in solving problems – not creating new ones!

Quotes of the day on choosing “Quality”

“The happiness of your life depends on the quality of your thoughts and decisions”.

“Associate with men and women of good quality if you value your own reputation.  It’s better to be alone than in bad company”.

“The way we communicate with others ultimately determines the quality of our lives.” (Do unto others as you would have them do unto you.)

“Courage is the #1 human quality, because it’s the quality which guarantees all the others”.