The Condensate System – An Important Item in Routine HVAC Maintenance


Expertise Includes:

    • Fires & Explosions
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    • Products Liability
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HVAC systems are almost everywhere in the United States now.  As a life-long resident of the humid south that grew up in a home without central air conditioning; I definitely appreciate the ability of a well-designed and maintained HVAC system to remove the oppressive summer humidity.

The very humidity that makes your clothes damp with sweat and hastened the invention of cooled leather seats in automobiles also has another route to create havoc…condensate.

In order for an HVAC or “air-conditioning system” to reduce the humidity in the air of your home or office it must first cool the air down to a point where the air can no longer keep the moisture in suspension as water vapor.  The moisture must condense… creating condensate.  This is what is happening when your cool beverage of choice “sweats” on the exterior of the container in the humid summer. Now that you have liquid water, as opposed to water vapor, this condensate must be directed out of your conditioned space to prevent water damage due to backed up or leaking condensate.

Secondary drain pan with float switch

The International Building Code, by way of the International Mechanical Code (IMC) has requirements for the handling of condensate.  Section 307 of the IMC states:

307.2 Evaporators and cooling coils.  Condensate drainage systems shall be provided for equipment and appliances containing evaporators or cooling coils.  Condensate drain systems shall be designed, constructed, and installed in accordance with Sections 307.2.1 through 307.2.4.

Of note for this blog is section 307.2.3 Auxiliary and secondary drain systems, which states:

In addition to the requirements of section 307.2.1, where damage to any building components could occur as a result of overflow from the equipment’s primary condensate removal system, one of the following auxiliary protection methods shall be provided for each cooling coil or fuel-fired appliance that produces condensate:

  1. An auxiliary drain pan with a separate drain shall be provided under the coils on which condensation will occur. The auxiliary pan drain shall discharge to a conspicuous point of disposal to alert occupants in the event of a stoppage of the primary drain……
  2. A separate overflow drain line shall be connected to the drain pan provided with the equipment. Such overflow drain shall discharge to a conspicuous point of disposal to alert occupants in the event of a stoppage of the primary drain.  The overflow drain line shall connect to the drain pan at a higher level than the primary drain connection.
  3. An auxiliary drain pan without a separate drain line shall be provided under the coils on which condensate will occur. Such pan shall be equipped with a water-level detection device conforming to UL 508 that will shut off the equipment served prior to overflow of the pan. ….
  4. A water-level detection device conforming to UL 508 shall be provided that will shut off the equipment served in the event that the primary drain is blocked. The device shall be installed in the primary drain line, the overflow drain line, or in the equipment-supplied drain pan, located at a point higher than the primary drain line connection and below the overflow rim of such pan.

Section 307.2.4 Traps states:  Condensate drains shall be trapped as required by the equipment or appliance manufacturer.

That’s a lot of words to say that the condensate created must be handled according to the manufacturer’s instructions, that a system must be present to remove the condensate from the structure, and a method of preventing damage from occurring to the structure should be present if the primary condensate system fails to properly remove the condensate from the structure.

Image credit: Primary drain pan switch

Image credit: Drain Pan

Condensate is generated when air is passed over the cooling coils at a temperature, usually around 55 degrees F, which causes the moisture in the air to condense on the coils and drain into the condensate pan.  From there the condensate must drain to a point outside the structure where it doesn’t cause damage.

The pool of condensate in the drain pan and the trap will, more likely than not, begin to grow algae over time.   Accumulation of algae can stop up the trap that is required by most manufacturers to allow the condensate to drain out of the condensate pan against the negative pressure created on the suction side of the supply fan.  If this trap becomes clogged with algae, then the condensate will have nowhere to go and can spill out of the primary drain pan.  If there is no secondary drain pan or a functional water level detecting switch in the secondary drain pan then the condensate can leak into the structure, causing water damage.   I have investigated claims for water damage where the condensate line was stopped up with algae.

Condensate pans, traps, and piping should be inspected regularly and serviced as necessary to prevent these types of backups.   The water level detection system must be properly installed in the condensate or secondary drain pan to shut the equipment down before the pan spills over the rim.   These level detection systems must also be wired properly into the HVAC thermostat or other control system in order to be effective.

Chad Jones, PE, CFEI, CMSE has a Bachelor of Science in Mechanical Engineering from Clemson University. Chad has over 20 years of engineering experience including mechanical, process, and manufacturing engineering. This work has included equipment design, machine safeguarding, cost estimating and safety compliance. Chad also has over 10 years of commercial, industrial, and residential HVAC and plumbing design experience. Chad is a Certified Fire and Explosion Investigator and IFSAC certified Firefighter II in Greenwood County, South Carolina.


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