What is a "high drain loop" or "air gap" in a dishwasher drain hose?
Sunday, October 6, 2019
They are the two ways to prevent backflow and get good drainage between a dishwasher and the drain connection at the sink tailpiece or disposal. It’s your choice of which one to use, but the code requires one or the other.
The Residential edition of the Florida Building Code, at 802.1.1.6, states that “the waste line of a domestic dishwashing machine discharging into a kitchen sink tailpiece or food waste disposer shall connect to a deck-mounted air gap OR the waste line shall rise and be securely fastened to the underside of the sink rim or counter.” The International Residential Code (IRC) has a similar citation.
The high drain loop is the simplest of the two options. It’s easy: just attach the drain line to the underside of the counter before it descends to the drain connection under the sink. Here’s a diagram from a GE installation manual.
The air gap (shown at top of page) is a device that is installed at the kitchen counter surface, usually to side of the sink faucet. It’s an unobtrusive, but not especially stylish, countertop detail. Some jurisdictions around the country (not Florida) require an air gap and will not accept a high drain loop. Because an air gap is not required in Florida, we rarely see one.
The most common dishwasher defect we find during a home inspection is lack of a high drain loop, which is sometimes referred to as an air gap loop.
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