A toilet flange is a mounting base for your toilet that's installed on top of a soil pipe that connects to the closet bend, the angled pipe leading to your drain. The flange has a flat surface with bolt-mounting slots on to which the toilet mounts, and it lies flat and flush with your floor. There are several sizes of flanges for different-size pipes. If you have not installed these flanges before, it's helpful to familiarize yourself with them.
Standard 4 x 3-Inch Toilet Flanges
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The most common and readily available toilet flange is the 4 x 3-inch size. This pipe is 4 inches wide at the top but only 3 inches wide at the bottom. The 3-inch bottom is the correct size for fitting the schedule 40 pipe most frequently used in home drains. The 4 inches at the top of the flange give you a little extra wiggle room, reducing the chances that water will seep through the wax ring when flushing the toilet. This is also the size of the closet bend pipe in most cases.
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The 3-Inch Flange
A 3-inch flange measures the same size as the schedule 40 pipe most likely used in your toilet drain. This flange doesn't give you the wiggle room of a 4-inch flange, which results in a bit more pressure on the flange when you flush the toilet. This is a known issue, however, so 3-inch flanges can handle the extra load.
When installing this type of flange, make sure your piping is the proper size. If your drain is not 3-inch pipe, consider using a different flange. You can install a reducing bushing to connect to a smaller pipe, but this raises the position of the flange and may affect the overall alignment of the plumbing.
The 4-Inch Flange
The 4-inch flange installs on both 4- and 3-inch drainpipes. This flange is manufactured so it fits over the top of a 3-inch pipe (in other words, the pipe slides into the flange), or the flange fits inside a 4-inch pipe (the flange slides into the 4-inch pipe). This flange is appropriate if you are unsure of the size of your toilet pipes or if you need to install a drainpipe between the flange and closet bend because you cannot directly connect the two.
Odd-Size Flanges
Other odd-size flanges exist. Typically, the flanges are similar in size to the 4 x 3-inch flange, however. An ABS plastic flange with a 3 1/2-inch bottom diameter and a 7-inch top diameter is available. This flange is often used to connect an ABS drainpipe to the toilet.
Extension kits to raise the height of the flange for new floor installations are also available. The flanges are the same diameter as standard flanges, and they simply extend the top of the flange upward to be flush with a new floor.
Offset Flanges and Their Uses
Offset flanges help those with older homes or elongated toilets connect their toilet to the drain. Offset flanges are the same diameter as standard flanges, but the barrel of the flange sits at a 45-degree angle. This helps move the toilet away from the wall if the plumbing is too close for modern toilet sizes. It also helps if you're replacing a standard round toilet with an elongated one.
Types of Flange Material
Size is the most important factor when replacing a toilet flange, but flanges are made of several different materials that you should be aware of. PVC is generally the most popular flange material. It's cheap, durable, easy to work with, and readily available. Copper flanges also last a long time and naturally resist bacteria, but copper is expensive and harder to work with. Brass toilet flanges are also durable but will oxidize if exposed to air.
If you find a stainless steel flange, understand that it may be a bit of a misnomer. Usually, only the wax ring portion of the flange features stainless steel. The rest is sometimes still made of plastic or copper. Cast-iron flanges are available but are meant only for use with cast-iron drainpipes. Avoid them unless you're already working with cast iron.