How to Reduce the Height of a Toilet Cast Iron Mounting Flange

Wear safety glasses to protect your eyes from flying shards of iron, and kneel down on the floor next to the cast iron toilet flange.

Place the tip of a cold chisel on top of the flange but not on the cast iron pipe that is located along the inner hole of the flange.

Hold the chisel firmly on one hand and hit the top of it using a 3-lb. sledge hammer. Keep the chisel in the same place and continue hitting it with firm pressure until a crack forms in the cast iron.

Move the chisel to the other side of the flange and repeat the procedure until a crack forms on that side as well.

Tap a wooden shim under the flange gently to protect the flooring. Insert a pry bar between the wooden shim and the cast iron flange. Press back on the bar handle to lift one side of the cracked flange out of the floor.

Insert the wooden shim under the remaining side of the cast iron flange and use the pry bar to remove that side as well.

Insert the metal part of a new compression flange into the hole, sliding the edges over the cast iron pipe still in the floor. If the flange is not flush with the floor, remove it and chisel away the floor material until it is flush.

Slide the round rubber flange gasket down over the cast iron floor pipe so that it rests between the pipe and the metal part of the flange.

Insert the brass ring on top of the rubber gasket aligning the holes in the ring with those in the metal flange. Tap the top of brass ring until it is flush with the floor.

Insert the four provided stainless steel bolts into the holes in the brass ring and tighten them firmly using a socket wrench.

Locate the two closet bolts, which are long and have an oval-shaped head. Turn them so the head faces the floor and then insert the heads into the oval openings in the flange. Slide the bolts forward until they are centered on either side of the flange. Proceed with installing the wax ring and the toilet.