The Drain Size for Draining a Washing Machine

Washing Machine Drain

• In older homes, the washing machine sometimes drains directly into the laundry room’s utility sink; when the appliance was installed, this wasn’t a code violation and it reduced the amount of work it took to connect it to the plumbing system. To accommodate modern building code guidelines, washing machines should connect to a standpipe drain, which in turn connects to the main drain line for the utility sink.

Minimum Size

• A laundry sink requires a 1 1/2-inch drain trap and trap arm. These can connect to a drainpipe of a minimum diameter of 1 1/2 inch. In most municipalities, you need at least a 2-inch standpipe with a 2-inch trap to drain a washing machine. If you already have a laundry sink with drain lines that meet the minimum code requirements, you can connect the standpipe to the 1 1/2-inch drainpipe and drain both the sink and washer through it.

Optimum Size

• When choosing drain size, take into account how large your washing machine is and how often you use it. For a small washer that is used only once or twice a week, holding to the minimum size for the drain will be fine. For a large front-load unit that will receive much use, a larger drain could help it get rid of used water more efficiently and prevent problems with blockages in the future. A 2 1/2- or 3-inch drain could be the better option. If you think that you might upgrade to a larger washing machine in the future, choosing a larger drain now could save you work down the line.

Considerations

• When planning to do plumbing work on your home, you might need to have plans reviewed by an inspector before you begin. Even if the inspection isn’t required, it can be helpful to have an experienced professional look over your plans. She can let you know if the minimum drain size will support your needs or if you should go larger.