Unintended water release in a residence is a frequent cause of damage (and insurance claims). Often, the water released is caused by a worn-out washing machine hose that ruptures, or an ice-maker supply tube that flexed one too many times and sprang a leak. These failures can result from a hose or tube defect, but often, they are caused by homeowner neglect or failure to replace an aged part.
When water damage begins suddenly in the attic space of a home, it may be tempting to blame it on a leaky roof. But if the weather has been clear for several days prior to the incident, an engineering investigation is in order.
Exactly this type of loss occurred in a 23-year-old Southern California townhouse. The homeowners awoke in the middle of the night when they heard running water and found their bedroom floor covered with about an inch of water. When the fire department responded to the homeowners’ emergency call, they found an air handling unit (AHU) in the attic was the source of the water streaming down the walls into the living space below. According to the homeowners, the air handler had been repaired in December, just two months before the incident, because it had not been providing any heat on cold nights during the early days of the winter season.
During our inspection, we discovered that the AHU contained 3 sets of coils: Two sets of coils in an older unit (blue and violet arrows in right photo below), and one additional coil that appeared brand new, but contained several cracked u-bends in the copper tubing (green arrows in left photo, coil removed in right photo). The first coil (blue arrow) was corroded and disconnected, and we determined that this was the hot water coil that had been in service until being replaced in December. The second coil (violet arrow) was connected to refrigerant tubing that ran outside to a compressor/condenser unit. And the third coil (green double arrow in left photo indicating cracked tubing) was located downstream of the other two.
The cracks were obviously the source of the water leak, and we hypothesized that they were caused by freezing of the water inside the tubes, but the sequence of events wasn’t obvious until we examined the weather history from December to February. That winter, the weather was generally mild, but there was (a) a cold spell in December, about the time the AHU was repaired; (b) a spell of unusually warm temperatures in January, when air conditioning was needed in the townhouse; and (c) another cold spell right when the water release occurred, a time when heating was needed again.
It was obvious that when the HVAC technician installed the new heating coil, he violated a well-known mechanical code requirement – never install a water coil downstream of a refrigerant coil because the chilled air is cold enough to freeze the water, which causes ice expansion that leads to bursting of tubing and piping. Clearly this aspect of the installation was defective, but additionally, there was yet another defect that contributed to the damage. He also failed to install a pan and drain underneath the new heating coil. When the homeowners called for heat during the February cold spell, and water began flowing out of the tubes that were ruptured during the January warm spell, it ran directly downward to the plywood flooring in the attic, rather than being directed outside via a drip pan and drain pipe.
The purpose of “Investigation Anecdotes” is to inform our readers about the intriguing field of engineering investigations. We hope you are instructed by this content, and we encourage you to contact us if you seek additional information. Copyright Martin Thermal Engineering, Inc. (2013)