Does code require a P-trap in an a/c condensate drain?
Saturday, September 25, 2021
Current IRC and Florida code (M1411.3) does not require a p-trap in the condensate drain line. It only specifies a minimum 1/8” per foot slope for the line, and that the condensate "shall not discharge into a street, alley or other areas where it would cause a nuisance.”
However, all building codes require following the manufacturer’s installation instructions and here’s where it gets interesting. Most manufacturers specify a trap in the line to avoid sucking or blowing air through the line between the evaporator coils and exterior termination of the drain. Some don’t require it, based on the design of their system. And several mini-split manufacturers specifically mandate no trap in the line.
There is, of course, an exception. A trap is listed in the Florida code in their “Standard for Mitigation of Radon in Existing Buildings” at the Appendix (E406.1.1): “If a portion of the condensate pipe does not drop below the height of the condensate drain outlet, then a trap shall be installed to prevent suction of outdoor air into the air handler.” But this is a standard for radon mitigation only.
A drain line p-trap is usually the right thing to do, and many HVAC contractors always include one, although they can clog and cause condensate backups into the air handler and plenum if the line is not regularly flushed. A newer air-type flow control device can be installed as an alternative that avoids this problem.
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