Washing Machine Drain Line Capacity

Importance

• The importance of understanding your washing machine drain line capacity is that that these lines will back up from time to time if they do not meet minimum capacity standards for water flow. A backup can cause significant damage throughout the home if the washer is located at a spot in the home where water overflow could cause wood rot or damage to baseboards and drywall.

Capacity

• The drain pipe into which your washing machine drain line feeds needs to be larger than the line protruding from your washing machine. Most washing machine lines are 1 inch in diameter and will have a fitting that will attach to the end of the drain pipe in which you intend for your water to go. The size of the fitting should provide you with an indication of the expected size that you need. Most drain pipes will be either 1 1/2 or 2 inches in diameter. Lines in older homes tend to be the former, while many new homes have a 2-inch washer drain. Having the drain pipe larger than the washer drain hose is by design, allowing air into the drain to improve flow.

Types

• Drain lines for washing machines are generally set up in one of two primary ways. In some cases, the machine will feed into what is known as a standpipe, which is a vertical drain line that feeds directly into the floor and ties into existing waste plumbing. Others may drain into a horizontal drain located in the floor. Those that are located in the floor will generally feed into pipe that slopes at a minimum of 1/4 inch per foot of piping.

Traps

• Washing machine drain lines need to have a vented trap, even if they tie into another existing drain line. Wastewater from a washing machine can develop a foul smell and create noxious odors that can affect the rest of the home. The trap needs to be removable so you can clean it out on occasion if debris builds up inside and clogs the drain.