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TACL B15309C

Spring, Texas

Serving the greater Houston, Texas area, including Tomball, Cypress, Waller, Magnolia, Montgomery, Conroe, The Woodlands, Willis, Kingwood, Crosby, Huntsville, Galveston, Pearland, Brazoria, Sugarland, Richmond, Katy, Humble, Kingwood,




Air conditioning drains can be the most frustrating of problems for homeowners and contractors alike. Their task is simple, but if an installer does not follow a few simple rules, the damage can be extensive. I have seen hundreds of condensate drains, and I would estimate that in most common mass produced homes outside of city inspections, less than 50% are installed per code in one manner or another.  There are several issues concerning condensate drains, that regard health as much as water damage.


The purpose of the drain is to allow the moisture removed from the air during the cooling process (a good thing in South Texas) to be delivered to a safe location, without introducing dangerous bacteria or odors to the air system. You may think, what? Yes, the drains usually connect to a sewer line and the drain process can work somewhat in reverse, and bring bacteria back into the air of your ac system if not installed with the proper protection. The protection is a simple device called a trap. This is simply a section of pipe with a small dip or U bend that isolates the air in your ac system from the air in your sewer. Sounds simple, but you would not believe how many systems we encounter that ignore this simple feature. Figure 1 shows some simple trap options. As you can see the trap simply holds an inch or two of water to prevent vapors from being sucked in to the ac system, or blowing conditioned air out into the sewer. It also restricts bacteria and vapors from backing up from the sewer system into the house air.




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Figure 2 shows a typical u-bend trap inline with a box coil. The other drain is connected to the secondary drain which does not require a trap and will be discussed in a moment.


Figure 3 shows what we call the termination, or the point that the ac drain connects to the house sewer system. This is the point of connection between the ac contractor and the plumbing contractor. This picture shows the 3/4” drain line connected to the drain line under a sink. By code this must be a bath sink, or a utility sink, but never a kitchen sink. The ac contractor can clear a line to this point. Beyond this, it must be handled by a licensed plumbing contractor. It also may drain to the outside and not the sewer system if city approved, and if the property has an on site septic system it will generally be draining outside.



Fig 4 shows a  very wrong termination into a vent pipe. Drains must go to an approved location!. Fig 5 shows a secondary pan under the main coil. Notice the primary drain off the coil does not have a trap, which is a violation. It is blowing ac air into the sewer!

SECONDARY DRAINS: Almost all systems require a secondary drain. This is a backup or emergency drain that only collects water when the primary drain fails, in other words is clogged. Most people looking at their equipment in the attic see the drain pan and figure it is the main drain system. The primary drain is internal to the unit, and if there is water in the exposed secondary drain pan it means something is wrong. To make the problem evident, the secondary drain is supposed to drain to a visible outdoor location. This is usually over a window, or over the roof. If you see water dripping from a pipe in an unusual location, your main drain is probably clogged, and the secondary emergency pan is in action. If you ignore this, and the secondary gets clogged, you may lose a ceiling from sheetrock damage.


FLOAT SWITCHES: A float switch is a device that senses a backup of drain water and will cut off the ac unit which will prevent the generation of any more condensate water. To the owner it will seem that the AC unit is broken, because it will remain off until the problem is resolved. This should avoid any problems with water damage through ceilings. Float switches are not required by code, except under certain situations, but certainly are a low cost safety feature. They can be a simple mechanical float, or an electronic sensor. They can be located in the drain line, or in the drain pan. Either way, they should shut the unit down in case of a water level problem.


DRAIN CLOGS: AC condensate drains are prone to clog. This is not so much because of debris from the system, but from natural growth in the water. Although there is a certain amount of sediment from corrosion  of the actual unit, the primary cause of drain clogging is from a growth of slime that thrives in the dark, cool wet environment of the drain tube. This slime does not create a hard clog, but since the drain is gravity fed only it has no pressure to overcome any slime that accumulates. As a result, any untreated drain pipes are prone to clogging at any given time, once the mold spores come to life. If you blow the line out, the untreated line is likely to clog again in a week or two. A drain cleaning should include a treatment with mold killing chemical, typically a bleach, and time release tablets to keep it clean for several months to come.