Size of Pipe for a Toilet Flange in Basement

Flange Defined

• The toilet flange is basically a section of your toilet drain pipe that has a flat head. The fitting secures the toilet to the floor, and it also connects the toilet to the home drain pipe under the floor. The pipe in the flange is sized to pair up with most home drains, which are 3 inches in diameter in the basement, and other stories. If you need to buy pipe to connect to the flange, 3-inch pipe is the best option. However, there are some cases where this is not the best choice.

Larger Drain Lines

• While most basement drain lines are 3 inches in diameter, some are larger. Many homes and industrial buildings have 4-inch drain pipes running to the major appliances. This drain pipe is the same size as the main drain lines that connect all the different appliances and drains throughout the home. If your drain pipe is 4 inches wide, your flange must accept 4-inch drain pipe, or you must use a reducing coupler to connect the two different sized lines.

Versatile Flange Sizes

• Some flanges are versatile and will connect to either 3-inch or 4-inch drain pipes. These flanges slide over the outside of the 3-inch drain pipe, and fit inside the 4-inch pipe. The versatility allows plumbers to connect both drain sizes without the use of reducing fittings, which is useful when a plumber services a variety of homes in the course of a week. If you are in doubt as to what size drain pipe you might need, install one of these flanges to make the installation easier. The flange you install in the basement is the same as one you install in an upstairs bath.

Connecting Pipes and Flanges

• Drain pipes fit right inside the outlet end of most flanges, as long as the flange is sized to the drain pipe. Since homes have standard sized plumbing today, you rarely find a misfitting flange and pipe. A variety of fittings exist to connect different sized pipes, so if you do have a problem, consult with an expert at a plumbing supply store and they can find the proper fitting for you. You rarely find flanges that connect to 5-inch pipes, because this pipe is just too large for your typical toilet. By the same token, flanges are not made to connect to 2-inch pipe because it is too thin for toilet drainage.