"Zone Forced Air - Condensate Plumbing"

 By Ron Stultz

Summary: When your AC runs, water condenses on the cool coils in the blower unit and have to be either run to a floor drain or be plumbed to drip or flow outside your home. Although, one would think this plumbing would not require maintenance it does periodically.

Background: When your AC is running, the coils in the blower get cold and water in the form of humdity present in the return duct work condensates on the coils and runs down to a tray that has a pipe connected to it. The purpose of this pipe is to route condensate to either a floor drain or to a location outside your home. On a hot humid day, an AC unit can condense gallons of water. Additionally, if a natural gas furnace is installed in your blower unit, it can be of the condensing type where water is extracted from the duct return air and again must be routed away from the blower unit.

In the image below, the condensate line out of the AC coil unit is shown.

In the image below, the black box in the lower, right corner, is the condensate from the natural gas furnace. As seen, its output is connected to the same pipe coming from the AC condensate line.

Hidden in this image but in the black section just above the huge white pipe is what is known as a "P Trap". The piece of pipe is shaped in such a way as to form a water barrier to any insects that might try to crawl up your condensate line and make a home in your blower unit.

In the image below, the condensate line is shown being run away from the blower unit where it eventually penetrates a brick wall and simply drips out on the outside of the house.

Maintenance? It is just pipes right so what is there to maintain??? Well, if for whatever reason, the condensate plumbing gets clogged, water will eventually leak down the inside of your blower unit and either into a collection pan installed there, or slowly but surely down to the inside of your finished home, ruining ceiling and perhaps walls. If there is a collection pan and the pan has a float valve on it, once the water level gets to a certain height, the blower unit will shut down and not allow a restart until all the water in the collection pan has been removed. Also note that some condensate float valves are installed in the actual condensate pipe and if the pipe is clogged, will shut down the blower unit and outside compressor. So what to maintain?

The condensate line can become clogged by mold or other debris (insect nest) and periodically, should be high pressure blown out followed by pouring liquid bleach down the line to kill any mold buildup.

In the image below, see the pipe sticking up off the condensate line with a cap on it? In my configuration, the cap is not glued to the pipe and can be removed. Once removed, an air compressor can be attached and the pile blown out. Also, at this point, liquid bleach can be powered down the pipe to kill mold.