Warning Signs of a Near Death HVAC System

What’s the average life of an HVAC system? The real answer, according to the U.S. Department of Energy, is the “end of it’s expected service life”.  That translates into real terms for the Air Conditioning System (AC) of about 10-15 years…and for a furnace or boiler, approximately 15-20 years.  In addition to age, as a primary factor in considering when to replace…a few other more obvious visible factors that should be factored in…as well as some more general symptoms that time for replacement is imminent…if not immediately needed are:

above ceiling view of a commercial cleanroom hvac installation

Air Conditioners

Since central AC systems have vital parts that are located outside…exterior to the building, they experience more exposure to weather changes and temperature fluctuations. As a result, they require more maintenance than a furnace does. So frequency of repairs becomes a major indicator as to when it’s time to replace the building’s AC system.  A general rule is that if more than one required service during a single season occurs due to mechanical issues, the AC system itself should be scrutinized more closely as to whether there are more fundamental issues involved.  A single malfunctioning part…or even a system that was improperly setup initially has the potential to trigger significant collateral damage to the overall AC system itself.  If that indeed occurs, merely replacing or fixing the original source problem doesn’t cancel out damage that other related parts have experienced as a result.  A common cause of spent or dead AC compressors is caused by accumulated acid that circulates in the system for some period of time.  Replacing the compressor is the obvious and necessary first step to getting the AC system back up and running. But if the acid isn’t thoroughly flushed out or any system leaks go unnoticed…the whole process could repeat shortly.

Excessive noise and impaired efficiency are two more symptoms of an AC system that’s diseased or wearing out.  While there are many reasons for the variety of awful sounds made by a system on it’s last leg, the likelihood that a serious issue is looming is too large to ignore.  However, replacing equipment outright isn’t always the final treatment required.


The heat exchanger in a gas fired furnace moves the heat produced by the gas burners…to the air that eventually circulates throughout the system and comes out the vent to warm up building occupants. Though a vital system component, the heat exchanger can also become vulnerable if it gets too hot, causing it to expand more than it was designed to.  The result…cracks that form in the heat exchanger…leading to eventual replacement of the component.  Dirty air filters can also cause the same problem over time…but usually it’s just the result of old age and deterioration.  Rust can also cause vulnerability to heat exchangers if the HVAC equipment is located in an area with excessive humidity…or if the the furnace is connected to a central  air conditioning unit that drips water onto the heat exchanger because of issues related to a faulty condensate drain or pan.

Warning signs to watch out for that indicate a dire heat exchanger issue are:

  1. Smell of exhaust in occupant or living space areas
  2. Soot visible on/near the heating vents in the occupant/living space
  3. Water visible under the furnace or corrosion inside the unit itself
  4. Your CO2 detector gets triggered during the Fall/Winter heating season ( call service technician immediately)


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