What Creates Coil Freeze Events?

pressure burst

What Creates Coil Freeze Events?

There are numerous reasons why water and steam coils can have major freeze events.   The damage is often extensive enough to require a coil replacement. The following reviews some of the major freeze event causes.


  • Coils not drained properly when winterized – This problem may be out of your control. Many chilled water coil circuits and placement of drains makes it impossible to fully drain the coil. Some manufacturers design uphill coil circuitry that prevents full drainage.


  • Steam coil selection and the system design prevent condensate from being removed – These problems include lack of installed vacuum breakers, improper sizing, location of the traps, and inadequate coil tube sizes and pitch. A steam coil in operation can have a freeze event if the condensate removal is inadequate.


  • Air stratification across the face of the coil – Air stratification can occur when preheat coils are located very close to an outside air damper or louver. High wind, along with just a minor mechanical breakdown, can create a rapid freeze event.


  • Mechanical Breakdown(s) – Breakdowns can be as simple as a valve malfunction, an inoperable pump, and/or a variety of freeze stat problems. Any or all of these can create a freeze event in a matter of minutes.

pressure burst

Freeze damage occurs when liquid inside the coil (heat exchanger) reduces its temperature and the liquid begins to turn into a solid (ice). Most people see this as an expansion of the ice that ultimately creates the damage. However, it is the increase in pressure inside the coil until it can’t be contained by the coil construction. A textbook freeze failure will always have bloating of the weakened area with a crack forming in the middle of the bloat.


Why is the damage often located at the back end of a return bend? Many times this is the weakest area of the coil, and the rising pressure seeks and finds this weak area.


Why is the damage sometimes located on the tubes and not on the return bend? The pressure builds, but so does the ice. Sometimes ice can form in the tubes and cut off the pressure to the outside of the coil (the return bend). This causes the tube to fail before the return bend fails.

Sentry Guard

USA Coil & Air has developed a patented coil series known as Sentry Guard™. We can’t prevent the actual freeze event, but we can prevent the damage to the coil from that event.


How is damage prevented by the Sentry Guard™ Coil design? The Sentry Guardrevolutionary freeze-relief plugs located on all the return bends and headers at both ends of the coil absorb the increased pressure and fail before the tubes and return bends. These screw-on/screw-off type plugs can be replaced easily, and the coil(s) becomes operable immediately. These plugs release the pressure at or about 650 PSI.   Our research has shown that damage to a tube or bend must exceed 1,000 PSI. The early release of pressure at 650 PSI gives you protection from any damage due to a freeze event.


We’ve recently heard of a design that we believe won’t work for many reasons. Those reasons include lack of coverage at both ends of the coil, the rearrangement of circuits that may reduce performance of the coil, and devices that occupy too much space, reducing the face area and performance even further.


Many fresh air systems are prone to a freeze event, and the down time and replacement is counterproductive and very costly. Examples are: hospitals, schools, universities, public areas, and specialized industrial processes. All of these have large percentages of air delivered from the outside.

Sentry Guard

USA Coil & Air has been building the Sentry Guardfor over 20 years. Our knowledge and experience provides you with a product that works, and we guarantee it!

USA Coil